Documentation/virt/kvm/api.txt

The Definitive KVM (Kernel-based Virtual Machine) API Documentation
===================================================================

1. General description
----------------------

The kvm API is a set of ioctls that are issued to control various aspects
of a virtual machine.  The ioctls belong to three classes:

 - System ioctls: These query and set global attributes which affect the
   whole kvm subsystem.  In addition a system ioctl is used to create
   virtual machines.

 - VM ioctls: These query and set attributes that affect an entire virtual
   machine, for example memory layout.  In addition a VM ioctl is used to
   create virtual cpus (vcpus) and devices.

   VM ioctls must be issued from the same process (address space) that was
   used to create the VM.

 - vcpu ioctls: These query and set attributes that control the operation
   of a single virtual cpu.

   vcpu ioctls should be issued from the same thread that was used to create
   the vcpu, except for asynchronous vcpu ioctl that are marked as such in
   the documentation.  Otherwise, the first ioctl after switching threads
   could see a performance impact.

 - device ioctls: These query and set attributes that control the operation
   of a single device.

   device ioctls must be issued from the same process (address space) that
   was used to create the VM.

2. File descriptors
-------------------

The kvm API is centered around file descriptors.  An initial
open("/dev/kvm") obtains a handle to the kvm subsystem; this handle
can be used to issue system ioctls.  A KVM_CREATE_VM ioctl on this
handle will create a VM file descriptor which can be used to issue VM
ioctls.  A KVM_CREATE_VCPU or KVM_CREATE_DEVICE ioctl on a VM fd will
create a virtual cpu or device and return a file descriptor pointing to
the new resource.  Finally, ioctls on a vcpu or device fd can be used
to control the vcpu or device.  For vcpus, this includes the important
task of actually running guest code.

In general file descriptors can be migrated among processes by means
of fork() and the SCM_RIGHTS facility of unix domain socket.  These
kinds of tricks are explicitly not supported by kvm.  While they will
not cause harm to the host, their actual behavior is not guaranteed by
the API.  See "General description" for details on the ioctl usage
model that is supported by KVM.

It is important to note that althought VM ioctls may only be issued from
the process that created the VM, a VM's lifecycle is associated with its
file descriptor, not its creator (process).  In other words, the VM and
its resources, *including the associated address space*, are not freed
until the last reference to the VM's file descriptor has been released.
For example, if fork() is issued after ioctl(KVM_CREATE_VM), the VM will
not be freed until both the parent (original) process and its child have
put their references to the VM's file descriptor.

Because a VM's resources are not freed until the last reference to its
file descriptor is released, creating additional references to a VM via
via fork(), dup(), etc... without careful consideration is strongly
discouraged and may have unwanted side effects, e.g. memory allocated
by and on behalf of the VM's process may not be freed/unaccounted when
the VM is shut down.


3. Extensions
-------------

As of Linux 2.6.22, the KVM ABI has been stabilized: no backward
incompatible change are allowed.  However, there is an extension
facility that allows backward-compatible extensions to the API to be
queried and used.

The extension mechanism is not based on the Linux version number.
Instead, kvm defines extension identifiers and a facility to query
whether a particular extension identifier is available.  If it is, a
set of ioctls is available for application use.


4. API description
------------------

This section describes ioctls that can be used to control kvm guests.
For each ioctl, the following information is provided along with a
description:

  Capability: which KVM extension provides this ioctl.  Can be 'basic',
      which means that is will be provided by any kernel that supports
      API version 12 (see section 4.1), a KVM_CAP_xyz constant, which
      means availability needs to be checked with KVM_CHECK_EXTENSION
      (see section 4.4), or 'none' which means that while not all kernels
      support this ioctl, there's no capability bit to check its
      availability: for kernels that don't support the ioctl,
      the ioctl returns -ENOTTY.

  Architectures: which instruction set architectures provide this ioctl.
      x86 includes both i386 and x86_64.

  Type: system, vm, or vcpu.

  Parameters: what parameters are accepted by the ioctl.

  Returns: the return value.  General error numbers (EBADF, ENOMEM, EINVAL)
      are not detailed, but errors with specific meanings are.


4.1 KVM_GET_API_VERSION

Capability: basic
Architectures: all
Type: system ioctl
Parameters: none
Returns: the constant KVM_API_VERSION (=12)

This identifies the API version as the stable kvm API. It is not
expected that this number will change.  However, Linux 2.6.20 and
2.6.21 report earlier versions; these are not documented and not
supported.  Applications should refuse to run if KVM_GET_API_VERSION
returns a value other than 12.  If this check passes, all ioctls
described as 'basic' will be available.


4.2 KVM_CREATE_VM

Capability: basic
Architectures: all
Type: system ioctl
Parameters: machine type identifier (KVM_VM_*)
Returns: a VM fd that can be used to control the new virtual machine.

The new VM has no virtual cpus and no memory.
You probably want to use 0 as machine type.

In order to create user controlled virtual machines on S390, check
KVM_CAP_S390_UCONTROL and use the flag KVM_VM_S390_UCONTROL as
privileged user (CAP_SYS_ADMIN).

To use hardware assisted virtualization on MIPS (VZ ASE) rather than
the default trap & emulate implementation (which changes the virtual
memory layout to fit in user mode), check KVM_CAP_MIPS_VZ and use the
flag KVM_VM_MIPS_VZ.


On arm64, the physical address size for a VM (IPA Size limit) is limited
to 40bits by default. The limit can be configured if the host supports the
extension KVM_CAP_ARM_VM_IPA_SIZE. When supported, use
KVM_VM_TYPE_ARM_IPA_SIZE(IPA_Bits) to set the size in the machine type
identifier, where IPA_Bits is the maximum width of any physical
address used by the VM. The IPA_Bits is encoded in bits[7-0] of the
machine type identifier.

e.g, to configure a guest to use 48bit physical address size :

    vm_fd = ioctl(dev_fd, KVM_CREATE_VM, KVM_VM_TYPE_ARM_IPA_SIZE(48));

The requested size (IPA_Bits) must be :
  0 - Implies default size, 40bits (for backward compatibility)

  or

  N - Implies N bits, where N is a positive integer such that,
      32 <= N <= Host_IPA_Limit

Host_IPA_Limit is the maximum possible value for IPA_Bits on the host and
is dependent on the CPU capability and the kernel configuration. The limit can
be retrieved using KVM_CAP_ARM_VM_IPA_SIZE of the KVM_CHECK_EXTENSION
ioctl() at run-time.

Please note that configuring the IPA size does not affect the capability
exposed by the guest CPUs in ID_AA64MMFR0_EL1[PARange]. It only affects
size of the address translated by the stage2 level (guest physical to
host physical address translations).


4.3 KVM_GET_MSR_INDEX_LIST, KVM_GET_MSR_FEATURE_INDEX_LIST

Capability: basic, KVM_CAP_GET_MSR_FEATURES for KVM_GET_MSR_FEATURE_INDEX_LIST
Architectures: x86
Type: system ioctl
Parameters: struct kvm_msr_list (in/out)
Returns: 0 on success; -1 on error
Errors:
  EFAULT:    the msr index list cannot be read from or written to
  E2BIG:     the msr index list is to be to fit in the array specified by
             the user.

struct kvm_msr_list {
	__u32 nmsrs; /* number of msrs in entries */
	__u32 indices[0];
};

The user fills in the size of the indices array in nmsrs, and in return
kvm adjusts nmsrs to reflect the actual number of msrs and fills in the
indices array with their numbers.

KVM_GET_MSR_INDEX_LIST returns the guest msrs that are supported.  The list
varies by kvm version and host processor, but does not change otherwise.

Note: if kvm indicates supports MCE (KVM_CAP_MCE), then the MCE bank MSRs are
not returned in the MSR list, as different vcpus can have a different number
of banks, as set via the KVM_X86_SETUP_MCE ioctl.

KVM_GET_MSR_FEATURE_INDEX_LIST returns the list of MSRs that can be passed
to the KVM_GET_MSRS system ioctl.  This lets userspace probe host capabilities
and processor features that are exposed via MSRs (e.g., VMX capabilities).
This list also varies by kvm version and host processor, but does not change
otherwise.


4.4 KVM_CHECK_EXTENSION

Capability: basic, KVM_CAP_CHECK_EXTENSION_VM for vm ioctl
Architectures: all
Type: system ioctl, vm ioctl
Parameters: extension identifier (KVM_CAP_*)
Returns: 0 if unsupported; 1 (or some other positive integer) if supported

The API allows the application to query about extensions to the core
kvm API.  Userspace passes an extension identifier (an integer) and
receives an integer that describes the extension availability.
Generally 0 means no and 1 means yes, but some extensions may report
additional information in the integer return value.

Based on their initialization different VMs may have different capabilities.
It is thus encouraged to use the vm ioctl to query for capabilities (available
with KVM_CAP_CHECK_EXTENSION_VM on the vm fd)

4.5 KVM_GET_VCPU_MMAP_SIZE

Capability: basic
Architectures: all
Type: system ioctl
Parameters: none
Returns: size of vcpu mmap area, in bytes

The KVM_RUN ioctl (cf.) communicates with userspace via a shared
memory region.  This ioctl returns the size of that region.  See the
KVM_RUN documentation for details.


4.6 KVM_SET_MEMORY_REGION

Capability: basic
Architectures: all
Type: vm ioctl
Parameters: struct kvm_memory_region (in)
Returns: 0 on success, -1 on error

This ioctl is obsolete and has been removed.


4.7 KVM_CREATE_VCPU

Capability: basic
Architectures: all
Type: vm ioctl
Parameters: vcpu id (apic id on x86)
Returns: vcpu fd on success, -1 on error

This API adds a vcpu to a virtual machine. No more than max_vcpus may be added.
The vcpu id is an integer in the range [0, max_vcpu_id).

The recommended max_vcpus value can be retrieved using the KVM_CAP_NR_VCPUS of
the KVM_CHECK_EXTENSION ioctl() at run-time.
The maximum possible value for max_vcpus can be retrieved using the
KVM_CAP_MAX_VCPUS of the KVM_CHECK_EXTENSION ioctl() at run-time.

If the KVM_CAP_NR_VCPUS does not exist, you should assume that max_vcpus is 4
cpus max.
If the KVM_CAP_MAX_VCPUS does not exist, you should assume that max_vcpus is
same as the value returned from KVM_CAP_NR_VCPUS.

The maximum possible value for max_vcpu_id can be retrieved using the
KVM_CAP_MAX_VCPU_ID of the KVM_CHECK_EXTENSION ioctl() at run-time.

If the KVM_CAP_MAX_VCPU_ID does not exist, you should assume that max_vcpu_id
is the same as the value returned from KVM_CAP_MAX_VCPUS.

On powerpc using book3s_hv mode, the vcpus are mapped onto virtual
threads in one or more virtual CPU cores.  (This is because the
hardware requires all the hardware threads in a CPU core to be in the
same partition.)  The KVM_CAP_PPC_SMT capability indicates the number
of vcpus per virtual core (vcore).  The vcore id is obtained by
dividing the vcpu id by the number of vcpus per vcore.  The vcpus in a
given vcore will always be in the same physical core as each other
(though that might be a different physical core from time to time).
Userspace can control the threading (SMT) mode of the guest by its
allocation of vcpu ids.  For example, if userspace wants
single-threaded guest vcpus, it should make all vcpu ids be a multiple
of the number of vcpus per vcore.

For virtual cpus that have been created with S390 user controlled virtual
machines, the resulting vcpu fd can be memory mapped at page offset
KVM_S390_SIE_PAGE_OFFSET in order to obtain a memory map of the virtual
cpu's hardware control block.


4.8 KVM_GET_DIRTY_LOG (vm ioctl)

Capability: basic
Architectures: all
Type: vm ioctl
Parameters: struct kvm_dirty_log (in/out)
Returns: 0 on success, -1 on error

/* for KVM_GET_DIRTY_LOG */
struct kvm_dirty_log {
	__u32 slot;
	__u32 padding;
	union {
		void __user *dirty_bitmap; /* one bit per page */
		__u64 padding;
	};
};

Given a memory slot, return a bitmap containing any pages dirtied
since the last call to this ioctl.  Bit 0 is the first page in the
memory slot.  Ensure the entire structure is cleared to avoid padding
issues.

If KVM_CAP_MULTI_ADDRESS_SPACE is available, bits 16-31 specifies
the address space for which you want to return the dirty bitmap.
They must be less than the value that KVM_CHECK_EXTENSION returns for
the KVM_CAP_MULTI_ADDRESS_SPACE capability.

The bits in the dirty bitmap are cleared before the ioctl returns, unless
KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 is enabled.  For more information,
see the description of the capability.

4.9 KVM_SET_MEMORY_ALIAS

Capability: basic
Architectures: x86
Type: vm ioctl
Parameters: struct kvm_memory_alias (in)
Returns: 0 (success), -1 (error)

This ioctl is obsolete and has been removed.


4.10 KVM_RUN

Capability: basic
Architectures: all
Type: vcpu ioctl
Parameters: none
Returns: 0 on success, -1 on error
Errors:
  EINTR:     an unmasked signal is pending

This ioctl is used to run a guest virtual cpu.  While there are no
explicit parameters, there is an implicit parameter block that can be
obtained by mmap()ing the vcpu fd at offset 0, with the size given by
KVM_GET_VCPU_MMAP_SIZE.  The parameter block is formatted as a 'struct
kvm_run' (see below).


4.11 KVM_GET_REGS

Capability: basic
Architectures: all except ARM, arm64
Type: vcpu ioctl
Parameters: struct kvm_regs (out)
Returns: 0 on success, -1 on error

Reads the general purpose registers from the vcpu.

/* x86 */
struct kvm_regs {
	/* out (KVM_GET_REGS) / in (KVM_SET_REGS) */
	__u64 rax, rbx, rcx, rdx;
	__u64 rsi, rdi, rsp, rbp;
	__u64 r8,  r9,  r10, r11;
	__u64 r12, r13, r14, r15;
	__u64 rip, rflags;
};

/* mips */
struct kvm_regs {
	/* out (KVM_GET_REGS) / in (KVM_SET_REGS) */
	__u64 gpr[32];
	__u64 hi;
	__u64 lo;
	__u64 pc;
};


4.12 KVM_SET_REGS

Capability: basic
Architectures: all except ARM, arm64
Type: vcpu ioctl
Parameters: struct kvm_regs (in)
Returns: 0 on success, -1 on error

Writes the general purpose registers into the vcpu.

See KVM_GET_REGS for the data structure.


4.13 KVM_GET_SREGS

Capability: basic
Architectures: x86, ppc
Type: vcpu ioctl
Parameters: struct kvm_sregs (out)
Returns: 0 on success, -1 on error

Reads special registers from the vcpu.

/* x86 */
struct kvm_sregs {
	struct kvm_segment cs, ds, es, fs, gs, ss;
	struct kvm_segment tr, ldt;
	struct kvm_dtable gdt, idt;
	__u64 cr0, cr2, cr3, cr4, cr8;
	__u64 efer;
	__u64 apic_base;
	__u64 interrupt_bitmap[(KVM_NR_INTERRUPTS + 63) / 64];
};

/* ppc -- see arch/powerpc/include/uapi/asm/kvm.h */

interrupt_bitmap is a bitmap of pending external interrupts.  At most
one bit may be set.  This interrupt has been acknowledged by the APIC
but not yet injected into the cpu core.


4.14 KVM_SET_SREGS

Capability: basic
Architectures: x86, ppc
Type: vcpu ioctl
Parameters: struct kvm_sregs (in)
Returns: 0 on success, -1 on error

Writes special registers into the vcpu.  See KVM_GET_SREGS for the
data structures.


4.15 KVM_TRANSLATE

Capability: basic
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_translation (in/out)
Returns: 0 on success, -1 on error

Translates a virtual address according to the vcpu's current address
translation mode.

struct kvm_translation {
	/* in */
	__u64 linear_address;

	/* out */
	__u64 physical_address;
	__u8  valid;
	__u8  writeable;
	__u8  usermode;
	__u8  pad[5];
};


4.16 KVM_INTERRUPT

Capability: basic
Architectures: x86, ppc, mips
Type: vcpu ioctl
Parameters: struct kvm_interrupt (in)
Returns: 0 on success, negative on failure.

Queues a hardware interrupt vector to be injected.

/* for KVM_INTERRUPT */
struct kvm_interrupt {
	/* in */
	__u32 irq;
};

X86:

Returns: 0 on success,
	 -EEXIST if an interrupt is already enqueued
	 -EINVAL the the irq number is invalid
	 -ENXIO if the PIC is in the kernel
	 -EFAULT if the pointer is invalid

Note 'irq' is an interrupt vector, not an interrupt pin or line. This
ioctl is useful if the in-kernel PIC is not used.

PPC:

Queues an external interrupt to be injected. This ioctl is overleaded
with 3 different irq values:

a) KVM_INTERRUPT_SET

  This injects an edge type external interrupt into the guest once it's ready
  to receive interrupts. When injected, the interrupt is done.

b) KVM_INTERRUPT_UNSET

  This unsets any pending interrupt.

  Only available with KVM_CAP_PPC_UNSET_IRQ.

c) KVM_INTERRUPT_SET_LEVEL

  This injects a level type external interrupt into the guest context. The
  interrupt stays pending until a specific ioctl with KVM_INTERRUPT_UNSET
  is triggered.

  Only available with KVM_CAP_PPC_IRQ_LEVEL.

Note that any value for 'irq' other than the ones stated above is invalid
and incurs unexpected behavior.

This is an asynchronous vcpu ioctl and can be invoked from any thread.

MIPS:

Queues an external interrupt to be injected into the virtual CPU. A negative
interrupt number dequeues the interrupt.

This is an asynchronous vcpu ioctl and can be invoked from any thread.


4.17 KVM_DEBUG_GUEST

Capability: basic
Architectures: none
Type: vcpu ioctl
Parameters: none)
Returns: -1 on error

Support for this has been removed.  Use KVM_SET_GUEST_DEBUG instead.


4.18 KVM_GET_MSRS

Capability: basic (vcpu), KVM_CAP_GET_MSR_FEATURES (system)
Architectures: x86
Type: system ioctl, vcpu ioctl
Parameters: struct kvm_msrs (in/out)
Returns: number of msrs successfully returned;
        -1 on error

When used as a system ioctl:
Reads the values of MSR-based features that are available for the VM.  This
is similar to KVM_GET_SUPPORTED_CPUID, but it returns MSR indices and values.
The list of msr-based features can be obtained using KVM_GET_MSR_FEATURE_INDEX_LIST
in a system ioctl.

When used as a vcpu ioctl:
Reads model-specific registers from the vcpu.  Supported msr indices can
be obtained using KVM_GET_MSR_INDEX_LIST in a system ioctl.

struct kvm_msrs {
	__u32 nmsrs; /* number of msrs in entries */
	__u32 pad;

	struct kvm_msr_entry entries[0];
};

struct kvm_msr_entry {
	__u32 index;
	__u32 reserved;
	__u64 data;
};

Application code should set the 'nmsrs' member (which indicates the
size of the entries array) and the 'index' member of each array entry.
kvm will fill in the 'data' member.


4.19 KVM_SET_MSRS

Capability: basic
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_msrs (in)
Returns: number of msrs successfully set (see below), -1 on error

Writes model-specific registers to the vcpu.  See KVM_GET_MSRS for the
data structures.

Application code should set the 'nmsrs' member (which indicates the
size of the entries array), and the 'index' and 'data' members of each
array entry.

It tries to set the MSRs in array entries[] one by one. If setting an MSR
fails, e.g., due to setting reserved bits, the MSR isn't supported/emulated
by KVM, etc..., it stops processing the MSR list and returns the number of
MSRs that have been set successfully.


4.20 KVM_SET_CPUID

Capability: basic
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_cpuid (in)
Returns: 0 on success, -1 on error

Defines the vcpu responses to the cpuid instruction.  Applications
should use the KVM_SET_CPUID2 ioctl if available.


struct kvm_cpuid_entry {
	__u32 function;
	__u32 eax;
	__u32 ebx;
	__u32 ecx;
	__u32 edx;
	__u32 padding;
};

/* for KVM_SET_CPUID */
struct kvm_cpuid {
	__u32 nent;
	__u32 padding;
	struct kvm_cpuid_entry entries[0];
};


4.21 KVM_SET_SIGNAL_MASK

Capability: basic
Architectures: all
Type: vcpu ioctl
Parameters: struct kvm_signal_mask (in)
Returns: 0 on success, -1 on error

Defines which signals are blocked during execution of KVM_RUN.  This
signal mask temporarily overrides the threads signal mask.  Any
unblocked signal received (except SIGKILL and SIGSTOP, which retain
their traditional behaviour) will cause KVM_RUN to return with -EINTR.

Note the signal will only be delivered if not blocked by the original
signal mask.

/* for KVM_SET_SIGNAL_MASK */
struct kvm_signal_mask {
	__u32 len;
	__u8  sigset[0];
};


4.22 KVM_GET_FPU

Capability: basic
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_fpu (out)
Returns: 0 on success, -1 on error

Reads the floating point state from the vcpu.

/* for KVM_GET_FPU and KVM_SET_FPU */
struct kvm_fpu {
	__u8  fpr[8][16];
	__u16 fcw;
	__u16 fsw;
	__u8  ftwx;  /* in fxsave format */
	__u8  pad1;
	__u16 last_opcode;
	__u64 last_ip;
	__u64 last_dp;
	__u8  xmm[16][16];
	__u32 mxcsr;
	__u32 pad2;
};


4.23 KVM_SET_FPU

Capability: basic
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_fpu (in)
Returns: 0 on success, -1 on error

Writes the floating point state to the vcpu.

/* for KVM_GET_FPU and KVM_SET_FPU */
struct kvm_fpu {
	__u8  fpr[8][16];
	__u16 fcw;
	__u16 fsw;
	__u8  ftwx;  /* in fxsave format */
	__u8  pad1;
	__u16 last_opcode;
	__u64 last_ip;
	__u64 last_dp;
	__u8  xmm[16][16];
	__u32 mxcsr;
	__u32 pad2;
};


4.24 KVM_CREATE_IRQCHIP

Capability: KVM_CAP_IRQCHIP, KVM_CAP_S390_IRQCHIP (s390)
Architectures: x86, ARM, arm64, s390
Type: vm ioctl
Parameters: none
Returns: 0 on success, -1 on error

Creates an interrupt controller model in the kernel.
On x86, creates a virtual ioapic, a virtual PIC (two PICs, nested), and sets up
future vcpus to have a local APIC.  IRQ routing for GSIs 0-15 is set to both
PIC and IOAPIC; GSI 16-23 only go to the IOAPIC.
On ARM/arm64, a GICv2 is created. Any other GIC versions require the usage of
KVM_CREATE_DEVICE, which also supports creating a GICv2.  Using
KVM_CREATE_DEVICE is preferred over KVM_CREATE_IRQCHIP for GICv2.
On s390, a dummy irq routing table is created.

Note that on s390 the KVM_CAP_S390_IRQCHIP vm capability needs to be enabled
before KVM_CREATE_IRQCHIP can be used.


4.25 KVM_IRQ_LINE

Capability: KVM_CAP_IRQCHIP
Architectures: x86, arm, arm64
Type: vm ioctl
Parameters: struct kvm_irq_level
Returns: 0 on success, -1 on error

Sets the level of a GSI input to the interrupt controller model in the kernel.
On some architectures it is required that an interrupt controller model has
been previously created with KVM_CREATE_IRQCHIP.  Note that edge-triggered
interrupts require the level to be set to 1 and then back to 0.

On real hardware, interrupt pins can be active-low or active-high.  This
does not matter for the level field of struct kvm_irq_level: 1 always
means active (asserted), 0 means inactive (deasserted).

x86 allows the operating system to program the interrupt polarity
(active-low/active-high) for level-triggered interrupts, and KVM used
to consider the polarity.  However, due to bitrot in the handling of
active-low interrupts, the above convention is now valid on x86 too.
This is signaled by KVM_CAP_X86_IOAPIC_POLARITY_IGNORED.  Userspace
should not present interrupts to the guest as active-low unless this
capability is present (or unless it is not using the in-kernel irqchip,
of course).


ARM/arm64 can signal an interrupt either at the CPU level, or at the
in-kernel irqchip (GIC), and for in-kernel irqchip can tell the GIC to
use PPIs designated for specific cpus.  The irq field is interpreted
like this:

  bits:  |  31 ... 28  | 27 ... 24 | 23  ... 16 | 15 ... 0 |
  field: | vcpu2_index | irq_type  | vcpu_index |  irq_id  |

The irq_type field has the following values:
- irq_type[0]: out-of-kernel GIC: irq_id 0 is IRQ, irq_id 1 is FIQ
- irq_type[1]: in-kernel GIC: SPI, irq_id between 32 and 1019 (incl.)
               (the vcpu_index field is ignored)
- irq_type[2]: in-kernel GIC: PPI, irq_id between 16 and 31 (incl.)

(The irq_id field thus corresponds nicely to the IRQ ID in the ARM GIC specs)

In both cases, level is used to assert/deassert the line.

When KVM_CAP_ARM_IRQ_LINE_LAYOUT_2 is supported, the target vcpu is
identified as (256 * vcpu2_index + vcpu_index). Otherwise, vcpu2_index
must be zero.

Note that on arm/arm64, the KVM_CAP_IRQCHIP capability only conditions
injection of interrupts for the in-kernel irqchip. KVM_IRQ_LINE can always
be used for a userspace interrupt controller.

struct kvm_irq_level {
	union {
		__u32 irq;     /* GSI */
		__s32 status;  /* not used for KVM_IRQ_LEVEL */
	};
	__u32 level;           /* 0 or 1 */
};


4.26 KVM_GET_IRQCHIP

Capability: KVM_CAP_IRQCHIP
Architectures: x86
Type: vm ioctl
Parameters: struct kvm_irqchip (in/out)
Returns: 0 on success, -1 on error

Reads the state of a kernel interrupt controller created with
KVM_CREATE_IRQCHIP into a buffer provided by the caller.

struct kvm_irqchip {
	__u32 chip_id;  /* 0 = PIC1, 1 = PIC2, 2 = IOAPIC */
	__u32 pad;
        union {
		char dummy[512];  /* reserving space */
		struct kvm_pic_state pic;
		struct kvm_ioapic_state ioapic;
	} chip;
};


4.27 KVM_SET_IRQCHIP

Capability: KVM_CAP_IRQCHIP
Architectures: x86
Type: vm ioctl
Parameters: struct kvm_irqchip (in)
Returns: 0 on success, -1 on error

Sets the state of a kernel interrupt controller created with
KVM_CREATE_IRQCHIP from a buffer provided by the caller.

struct kvm_irqchip {
	__u32 chip_id;  /* 0 = PIC1, 1 = PIC2, 2 = IOAPIC */
	__u32 pad;
        union {
		char dummy[512];  /* reserving space */
		struct kvm_pic_state pic;
		struct kvm_ioapic_state ioapic;
	} chip;
};


4.28 KVM_XEN_HVM_CONFIG

Capability: KVM_CAP_XEN_HVM
Architectures: x86
Type: vm ioctl
Parameters: struct kvm_xen_hvm_config (in)
Returns: 0 on success, -1 on error

Sets the MSR that the Xen HVM guest uses to initialize its hypercall
page, and provides the starting address and size of the hypercall
blobs in userspace.  When the guest writes the MSR, kvm copies one
page of a blob (32- or 64-bit, depending on the vcpu mode) to guest
memory.

struct kvm_xen_hvm_config {
	__u32 flags;
	__u32 msr;
	__u64 blob_addr_32;
	__u64 blob_addr_64;
	__u8 blob_size_32;
	__u8 blob_size_64;
	__u8 pad2[30];
};


4.29 KVM_GET_CLOCK

Capability: KVM_CAP_ADJUST_CLOCK
Architectures: x86
Type: vm ioctl
Parameters: struct kvm_clock_data (out)
Returns: 0 on success, -1 on error

Gets the current timestamp of kvmclock as seen by the current guest. In
conjunction with KVM_SET_CLOCK, it is used to ensure monotonicity on scenarios
such as migration.

When KVM_CAP_ADJUST_CLOCK is passed to KVM_CHECK_EXTENSION, it returns the
set of bits that KVM can return in struct kvm_clock_data's flag member.

The only flag defined now is KVM_CLOCK_TSC_STABLE.  If set, the returned
value is the exact kvmclock value seen by all VCPUs at the instant
when KVM_GET_CLOCK was called.  If clear, the returned value is simply
CLOCK_MONOTONIC plus a constant offset; the offset can be modified
with KVM_SET_CLOCK.  KVM will try to make all VCPUs follow this clock,
but the exact value read by each VCPU could differ, because the host
TSC is not stable.

struct kvm_clock_data {
	__u64 clock;  /* kvmclock current value */
	__u32 flags;
	__u32 pad[9];
};


4.30 KVM_SET_CLOCK

Capability: KVM_CAP_ADJUST_CLOCK
Architectures: x86
Type: vm ioctl
Parameters: struct kvm_clock_data (in)
Returns: 0 on success, -1 on error

Sets the current timestamp of kvmclock to the value specified in its parameter.
In conjunction with KVM_GET_CLOCK, it is used to ensure monotonicity on scenarios
such as migration.

struct kvm_clock_data {
	__u64 clock;  /* kvmclock current value */
	__u32 flags;
	__u32 pad[9];
};


4.31 KVM_GET_VCPU_EVENTS

Capability: KVM_CAP_VCPU_EVENTS
Extended by: KVM_CAP_INTR_SHADOW
Architectures: x86, arm, arm64
Type: vcpu ioctl
Parameters: struct kvm_vcpu_event (out)
Returns: 0 on success, -1 on error

X86:

Gets currently pending exceptions, interrupts, and NMIs as well as related
states of the vcpu.

struct kvm_vcpu_events {
	struct {
		__u8 injected;
		__u8 nr;
		__u8 has_error_code;
		__u8 pending;
		__u32 error_code;
	} exception;
	struct {
		__u8 injected;
		__u8 nr;
		__u8 soft;
		__u8 shadow;
	} interrupt;
	struct {
		__u8 injected;
		__u8 pending;
		__u8 masked;
		__u8 pad;
	} nmi;
	__u32 sipi_vector;
	__u32 flags;
	struct {
		__u8 smm;
		__u8 pending;
		__u8 smm_inside_nmi;
		__u8 latched_init;
	} smi;
	__u8 reserved[27];
	__u8 exception_has_payload;
	__u64 exception_payload;
};

The following bits are defined in the flags field:

- KVM_VCPUEVENT_VALID_SHADOW may be set to signal that
  interrupt.shadow contains a valid state.

- KVM_VCPUEVENT_VALID_SMM may be set to signal that smi contains a
  valid state.

- KVM_VCPUEVENT_VALID_PAYLOAD may be set to signal that the
  exception_has_payload, exception_payload, and exception.pending
  fields contain a valid state. This bit will be set whenever
  KVM_CAP_EXCEPTION_PAYLOAD is enabled.

ARM/ARM64:

If the guest accesses a device that is being emulated by the host kernel in
such a way that a real device would generate a physical SError, KVM may make
a virtual SError pending for that VCPU. This system error interrupt remains
pending until the guest takes the exception by unmasking PSTATE.A.

Running the VCPU may cause it to take a pending SError, or make an access that
causes an SError to become pending. The event's description is only valid while
the VPCU is not running.

This API provides a way to read and write the pending 'event' state that is not
visible to the guest. To save, restore or migrate a VCPU the struct representing
the state can be read then written using this GET/SET API, along with the other
guest-visible registers. It is not possible to 'cancel' an SError that has been
made pending.

A device being emulated in user-space may also wish to generate an SError. To do
this the events structure can be populated by user-space. The current state
should be read first, to ensure no existing SError is pending. If an existing
SError is pending, the architecture's 'Multiple SError interrupts' rules should
be followed. (2.5.3 of DDI0587.a "ARM Reliability, Availability, and
Serviceability (RAS) Specification").

SError exceptions always have an ESR value. Some CPUs have the ability to
specify what the virtual SError's ESR value should be. These systems will
advertise KVM_CAP_ARM_INJECT_SERROR_ESR. In this case exception.has_esr will
always have a non-zero value when read, and the agent making an SError pending
should specify the ISS field in the lower 24 bits of exception.serror_esr. If
the system supports KVM_CAP_ARM_INJECT_SERROR_ESR, but user-space sets the events
with exception.has_esr as zero, KVM will choose an ESR.

Specifying exception.has_esr on a system that does not support it will return
-EINVAL. Setting anything other than the lower 24bits of exception.serror_esr
will return -EINVAL.

struct kvm_vcpu_events {
	struct {
		__u8 serror_pending;
		__u8 serror_has_esr;
		/* Align it to 8 bytes */
		__u8 pad[6];
		__u64 serror_esr;
	} exception;
	__u32 reserved[12];
};

4.32 KVM_SET_VCPU_EVENTS

Capability: KVM_CAP_VCPU_EVENTS
Extended by: KVM_CAP_INTR_SHADOW
Architectures: x86, arm, arm64
Type: vcpu ioctl
Parameters: struct kvm_vcpu_event (in)
Returns: 0 on success, -1 on error

X86:

Set pending exceptions, interrupts, and NMIs as well as related states of the
vcpu.

See KVM_GET_VCPU_EVENTS for the data structure.

Fields that may be modified asynchronously by running VCPUs can be excluded
from the update. These fields are nmi.pending, sipi_vector, smi.smm,
smi.pending. Keep the corresponding bits in the flags field cleared to
suppress overwriting the current in-kernel state. The bits are:

KVM_VCPUEVENT_VALID_NMI_PENDING - transfer nmi.pending to the kernel
KVM_VCPUEVENT_VALID_SIPI_VECTOR - transfer sipi_vector
KVM_VCPUEVENT_VALID_SMM         - transfer the smi sub-struct.

If KVM_CAP_INTR_SHADOW is available, KVM_VCPUEVENT_VALID_SHADOW can be set in
the flags field to signal that interrupt.shadow contains a valid state and
shall be written into the VCPU.

KVM_VCPUEVENT_VALID_SMM can only be set if KVM_CAP_X86_SMM is available.

If KVM_CAP_EXCEPTION_PAYLOAD is enabled, KVM_VCPUEVENT_VALID_PAYLOAD
can be set in the flags field to signal that the
exception_has_payload, exception_payload, and exception.pending fields
contain a valid state and shall be written into the VCPU.

ARM/ARM64:

Set the pending SError exception state for this VCPU. It is not possible to
'cancel' an Serror that has been made pending.

See KVM_GET_VCPU_EVENTS for the data structure.


4.33 KVM_GET_DEBUGREGS

Capability: KVM_CAP_DEBUGREGS
Architectures: x86
Type: vm ioctl
Parameters: struct kvm_debugregs (out)
Returns: 0 on success, -1 on error

Reads debug registers from the vcpu.

struct kvm_debugregs {
	__u64 db[4];
	__u64 dr6;
	__u64 dr7;
	__u64 flags;
	__u64 reserved[9];
};


4.34 KVM_SET_DEBUGREGS

Capability: KVM_CAP_DEBUGREGS
Architectures: x86
Type: vm ioctl
Parameters: struct kvm_debugregs (in)
Returns: 0 on success, -1 on error

Writes debug registers into the vcpu.

See KVM_GET_DEBUGREGS for the data structure. The flags field is unused
yet and must be cleared on entry.


4.35 KVM_SET_USER_MEMORY_REGION

Capability: KVM_CAP_USER_MEMORY
Architectures: all
Type: vm ioctl
Parameters: struct kvm_userspace_memory_region (in)
Returns: 0 on success, -1 on error

struct kvm_userspace_memory_region {
	__u32 slot;
	__u32 flags;
	__u64 guest_phys_addr;
	__u64 memory_size; /* bytes */
	__u64 userspace_addr; /* start of the userspace allocated memory */
};

/* for kvm_memory_region::flags */
#define KVM_MEM_LOG_DIRTY_PAGES	(1UL << 0)
#define KVM_MEM_READONLY	(1UL << 1)

This ioctl allows the user to create, modify or delete a guest physical
memory slot.  Bits 0-15 of "slot" specify the slot id and this value
should be less than the maximum number of user memory slots supported per
VM.  The maximum allowed slots can be queried using KVM_CAP_NR_MEMSLOTS.
Slots may not overlap in guest physical address space.

If KVM_CAP_MULTI_ADDRESS_SPACE is available, bits 16-31 of "slot"
specifies the address space which is being modified.  They must be
less than the value that KVM_CHECK_EXTENSION returns for the
KVM_CAP_MULTI_ADDRESS_SPACE capability.  Slots in separate address spaces
are unrelated; the restriction on overlapping slots only applies within
each address space.

Deleting a slot is done by passing zero for memory_size.  When changing
an existing slot, it may be moved in the guest physical memory space,
or its flags may be modified, but it may not be resized.

Memory for the region is taken starting at the address denoted by the
field userspace_addr, which must point at user addressable memory for
the entire memory slot size.  Any object may back this memory, including
anonymous memory, ordinary files, and hugetlbfs.

It is recommended that the lower 21 bits of guest_phys_addr and userspace_addr
be identical.  This allows large pages in the guest to be backed by large
pages in the host.

The flags field supports two flags: KVM_MEM_LOG_DIRTY_PAGES and
KVM_MEM_READONLY.  The former can be set to instruct KVM to keep track of
writes to memory within the slot.  See KVM_GET_DIRTY_LOG ioctl to know how to
use it.  The latter can be set, if KVM_CAP_READONLY_MEM capability allows it,
to make a new slot read-only.  In this case, writes to this memory will be
posted to userspace as KVM_EXIT_MMIO exits.

When the KVM_CAP_SYNC_MMU capability is available, changes in the backing of
the memory region are automatically reflected into the guest.  For example, an
mmap() that affects the region will be made visible immediately.  Another
example is madvise(MADV_DROP).

It is recommended to use this API instead of the KVM_SET_MEMORY_REGION ioctl.
The KVM_SET_MEMORY_REGION does not allow fine grained control over memory
allocation and is deprecated.


4.36 KVM_SET_TSS_ADDR

Capability: KVM_CAP_SET_TSS_ADDR
Architectures: x86
Type: vm ioctl
Parameters: unsigned long tss_address (in)
Returns: 0 on success, -1 on error

This ioctl defines the physical address of a three-page region in the guest
physical address space.  The region must be within the first 4GB of the
guest physical address space and must not conflict with any memory slot
or any mmio address.  The guest may malfunction if it accesses this memory
region.

This ioctl is required on Intel-based hosts.  This is needed on Intel hardware
because of a quirk in the virtualization implementation (see the internals
documentation when it pops into existence).


4.37 KVM_ENABLE_CAP

Capability: KVM_CAP_ENABLE_CAP
Architectures: mips, ppc, s390
Type: vcpu ioctl
Parameters: struct kvm_enable_cap (in)
Returns: 0 on success; -1 on error

Capability: KVM_CAP_ENABLE_CAP_VM
Architectures: all
Type: vcpu ioctl
Parameters: struct kvm_enable_cap (in)
Returns: 0 on success; -1 on error

+Not all extensions are enabled by default. Using this ioctl the application
can enable an extension, making it available to the guest.

On systems that do not support this ioctl, it always fails. On systems that
do support it, it only works for extensions that are supported for enablement.

To check if a capability can be enabled, the KVM_CHECK_EXTENSION ioctl should
be used.

struct kvm_enable_cap {
       /* in */
       __u32 cap;

The capability that is supposed to get enabled.

       __u32 flags;

A bitfield indicating future enhancements. Has to be 0 for now.

       __u64 args[4];

Arguments for enabling a feature. If a feature needs initial values to
function properly, this is the place to put them.

       __u8  pad[64];
};

The vcpu ioctl should be used for vcpu-specific capabilities, the vm ioctl
for vm-wide capabilities.

4.38 KVM_GET_MP_STATE

Capability: KVM_CAP_MP_STATE
Architectures: x86, s390, arm, arm64
Type: vcpu ioctl
Parameters: struct kvm_mp_state (out)
Returns: 0 on success; -1 on error

struct kvm_mp_state {
	__u32 mp_state;
};

Returns the vcpu's current "multiprocessing state" (though also valid on
uniprocessor guests).

Possible values are:

 - KVM_MP_STATE_RUNNABLE:        the vcpu is currently running [x86,arm/arm64]
 - KVM_MP_STATE_UNINITIALIZED:   the vcpu is an application processor (AP)
                                 which has not yet received an INIT signal [x86]
 - KVM_MP_STATE_INIT_RECEIVED:   the vcpu has received an INIT signal, and is
                                 now ready for a SIPI [x86]
 - KVM_MP_STATE_HALTED:          the vcpu has executed a HLT instruction and
                                 is waiting for an interrupt [x86]
 - KVM_MP_STATE_SIPI_RECEIVED:   the vcpu has just received a SIPI (vector
                                 accessible via KVM_GET_VCPU_EVENTS) [x86]
 - KVM_MP_STATE_STOPPED:         the vcpu is stopped [s390,arm/arm64]
 - KVM_MP_STATE_CHECK_STOP:      the vcpu is in a special error state [s390]
 - KVM_MP_STATE_OPERATING:       the vcpu is operating (running or halted)
                                 [s390]
 - KVM_MP_STATE_LOAD:            the vcpu is in a special load/startup state
                                 [s390]

On x86, this ioctl is only useful after KVM_CREATE_IRQCHIP. Without an
in-kernel irqchip, the multiprocessing state must be maintained by userspace on
these architectures.

For arm/arm64:

The only states that are valid are KVM_MP_STATE_STOPPED and
KVM_MP_STATE_RUNNABLE which reflect if the vcpu is paused or not.

4.39 KVM_SET_MP_STATE

Capability: KVM_CAP_MP_STATE
Architectures: x86, s390, arm, arm64
Type: vcpu ioctl
Parameters: struct kvm_mp_state (in)
Returns: 0 on success; -1 on error

Sets the vcpu's current "multiprocessing state"; see KVM_GET_MP_STATE for
arguments.

On x86, this ioctl is only useful after KVM_CREATE_IRQCHIP. Without an
in-kernel irqchip, the multiprocessing state must be maintained by userspace on
these architectures.

For arm/arm64:

The only states that are valid are KVM_MP_STATE_STOPPED and
KVM_MP_STATE_RUNNABLE which reflect if the vcpu should be paused or not.

4.40 KVM_SET_IDENTITY_MAP_ADDR

Capability: KVM_CAP_SET_IDENTITY_MAP_ADDR
Architectures: x86
Type: vm ioctl
Parameters: unsigned long identity (in)
Returns: 0 on success, -1 on error

This ioctl defines the physical address of a one-page region in the guest
physical address space.  The region must be within the first 4GB of the
guest physical address space and must not conflict with any memory slot
or any mmio address.  The guest may malfunction if it accesses this memory
region.

Setting the address to 0 will result in resetting the address to its default
(0xfffbc000).

This ioctl is required on Intel-based hosts.  This is needed on Intel hardware
because of a quirk in the virtualization implementation (see the internals
documentation when it pops into existence).

Fails if any VCPU has already been created.

4.41 KVM_SET_BOOT_CPU_ID

Capability: KVM_CAP_SET_BOOT_CPU_ID
Architectures: x86
Type: vm ioctl
Parameters: unsigned long vcpu_id
Returns: 0 on success, -1 on error

Define which vcpu is the Bootstrap Processor (BSP).  Values are the same
as the vcpu id in KVM_CREATE_VCPU.  If this ioctl is not called, the default
is vcpu 0.


4.42 KVM_GET_XSAVE

Capability: KVM_CAP_XSAVE
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_xsave (out)
Returns: 0 on success, -1 on error

struct kvm_xsave {
	__u32 region[1024];
};

This ioctl would copy current vcpu's xsave struct to the userspace.


4.43 KVM_SET_XSAVE

Capability: KVM_CAP_XSAVE
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_xsave (in)
Returns: 0 on success, -1 on error

struct kvm_xsave {
	__u32 region[1024];
};

This ioctl would copy userspace's xsave struct to the kernel.


4.44 KVM_GET_XCRS

Capability: KVM_CAP_XCRS
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_xcrs (out)
Returns: 0 on success, -1 on error

struct kvm_xcr {
	__u32 xcr;
	__u32 reserved;
	__u64 value;
};

struct kvm_xcrs {
	__u32 nr_xcrs;
	__u32 flags;
	struct kvm_xcr xcrs[KVM_MAX_XCRS];
	__u64 padding[16];
};

This ioctl would copy current vcpu's xcrs to the userspace.


4.45 KVM_SET_XCRS

Capability: KVM_CAP_XCRS
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_xcrs (in)
Returns: 0 on success, -1 on error

struct kvm_xcr {
	__u32 xcr;
	__u32 reserved;
	__u64 value;
};

struct kvm_xcrs {
	__u32 nr_xcrs;
	__u32 flags;
	struct kvm_xcr xcrs[KVM_MAX_XCRS];
	__u64 padding[16];
};

This ioctl would set vcpu's xcr to the value userspace specified.


4.46 KVM_GET_SUPPORTED_CPUID

Capability: KVM_CAP_EXT_CPUID
Architectures: x86
Type: system ioctl
Parameters: struct kvm_cpuid2 (in/out)
Returns: 0 on success, -1 on error

struct kvm_cpuid2 {
	__u32 nent;
	__u32 padding;
	struct kvm_cpuid_entry2 entries[0];
};

#define KVM_CPUID_FLAG_SIGNIFCANT_INDEX		BIT(0)
#define KVM_CPUID_FLAG_STATEFUL_FUNC		BIT(1)
#define KVM_CPUID_FLAG_STATE_READ_NEXT		BIT(2)

struct kvm_cpuid_entry2 {
	__u32 function;
	__u32 index;
	__u32 flags;
	__u32 eax;
	__u32 ebx;
	__u32 ecx;
	__u32 edx;
	__u32 padding[3];
};

This ioctl returns x86 cpuid features which are supported by both the
hardware and kvm in its default configuration.  Userspace can use the
information returned by this ioctl to construct cpuid information (for
KVM_SET_CPUID2) that is consistent with hardware, kernel, and
userspace capabilities, and with user requirements (for example, the
user may wish to constrain cpuid to emulate older hardware, or for
feature consistency across a cluster).

Note that certain capabilities, such as KVM_CAP_X86_DISABLE_EXITS, may
expose cpuid features (e.g. MONITOR) which are not supported by kvm in
its default configuration. If userspace enables such capabilities, it
is responsible for modifying the results of this ioctl appropriately.

Userspace invokes KVM_GET_SUPPORTED_CPUID by passing a kvm_cpuid2 structure
with the 'nent' field indicating the number of entries in the variable-size
array 'entries'.  If the number of entries is too low to describe the cpu
capabilities, an error (E2BIG) is returned.  If the number is too high,
the 'nent' field is adjusted and an error (ENOMEM) is returned.  If the
number is just right, the 'nent' field is adjusted to the number of valid
entries in the 'entries' array, which is then filled.

The entries returned are the host cpuid as returned by the cpuid instruction,
with unknown or unsupported features masked out.  Some features (for example,
x2apic), may not be present in the host cpu, but are exposed by kvm if it can
emulate them efficiently. The fields in each entry are defined as follows:

  function: the eax value used to obtain the entry
  index: the ecx value used to obtain the entry (for entries that are
         affected by ecx)
  flags: an OR of zero or more of the following:
        KVM_CPUID_FLAG_SIGNIFCANT_INDEX:
           if the index field is valid
        KVM_CPUID_FLAG_STATEFUL_FUNC:
           if cpuid for this function returns different values for successive
           invocations; there will be several entries with the same function,
           all with this flag set
        KVM_CPUID_FLAG_STATE_READ_NEXT:
           for KVM_CPUID_FLAG_STATEFUL_FUNC entries, set if this entry is
           the first entry to be read by a cpu
   eax, ebx, ecx, edx: the values returned by the cpuid instruction for
         this function/index combination

The TSC deadline timer feature (CPUID leaf 1, ecx[24]) is always returned
as false, since the feature depends on KVM_CREATE_IRQCHIP for local APIC
support.  Instead it is reported via

  ioctl(KVM_CHECK_EXTENSION, KVM_CAP_TSC_DEADLINE_TIMER)

if that returns true and you use KVM_CREATE_IRQCHIP, or if you emulate the
feature in userspace, then you can enable the feature for KVM_SET_CPUID2.


4.47 KVM_PPC_GET_PVINFO

Capability: KVM_CAP_PPC_GET_PVINFO
Architectures: ppc
Type: vm ioctl
Parameters: struct kvm_ppc_pvinfo (out)
Returns: 0 on success, !0 on error

struct kvm_ppc_pvinfo {
	__u32 flags;
	__u32 hcall[4];
	__u8  pad[108];
};

This ioctl fetches PV specific information that need to be passed to the guest
using the device tree or other means from vm context.

The hcall array defines 4 instructions that make up a hypercall.

If any additional field gets added to this structure later on, a bit for that
additional piece of information will be set in the flags bitmap.

The flags bitmap is defined as:

   /* the host supports the ePAPR idle hcall
   #define KVM_PPC_PVINFO_FLAGS_EV_IDLE   (1<<0)

4.52 KVM_SET_GSI_ROUTING

Capability: KVM_CAP_IRQ_ROUTING
Architectures: x86 s390 arm arm64
Type: vm ioctl
Parameters: struct kvm_irq_routing (in)
Returns: 0 on success, -1 on error

Sets the GSI routing table entries, overwriting any previously set entries.

On arm/arm64, GSI routing has the following limitation:
- GSI routing does not apply to KVM_IRQ_LINE but only to KVM_IRQFD.

struct kvm_irq_routing {
	__u32 nr;
	__u32 flags;
	struct kvm_irq_routing_entry entries[0];
};

No flags are specified so far, the corresponding field must be set to zero.

struct kvm_irq_routing_entry {
	__u32 gsi;
	__u32 type;
	__u32 flags;
	__u32 pad;
	union {
		struct kvm_irq_routing_irqchip irqchip;
		struct kvm_irq_routing_msi msi;
		struct kvm_irq_routing_s390_adapter adapter;
		struct kvm_irq_routing_hv_sint hv_sint;
		__u32 pad[8];
	} u;
};

/* gsi routing entry types */
#define KVM_IRQ_ROUTING_IRQCHIP 1
#define KVM_IRQ_ROUTING_MSI 2
#define KVM_IRQ_ROUTING_S390_ADAPTER 3
#define KVM_IRQ_ROUTING_HV_SINT 4

flags:
- KVM_MSI_VALID_DEVID: used along with KVM_IRQ_ROUTING_MSI routing entry
  type, specifies that the devid field contains a valid value.  The per-VM
  KVM_CAP_MSI_DEVID capability advertises the requirement to provide
  the device ID.  If this capability is not available, userspace should
  never set the KVM_MSI_VALID_DEVID flag as the ioctl might fail.
- zero otherwise

struct kvm_irq_routing_irqchip {
	__u32 irqchip;
	__u32 pin;
};

struct kvm_irq_routing_msi {
	__u32 address_lo;
	__u32 address_hi;
	__u32 data;
	union {
		__u32 pad;
		__u32 devid;
	};
};

If KVM_MSI_VALID_DEVID is set, devid contains a unique device identifier
for the device that wrote the MSI message.  For PCI, this is usually a
BFD identifier in the lower 16 bits.

On x86, address_hi is ignored unless the KVM_X2APIC_API_USE_32BIT_IDS
feature of KVM_CAP_X2APIC_API capability is enabled.  If it is enabled,
address_hi bits 31-8 provide bits 31-8 of the destination id.  Bits 7-0 of
address_hi must be zero.

struct kvm_irq_routing_s390_adapter {
	__u64 ind_addr;
	__u64 summary_addr;
	__u64 ind_offset;
	__u32 summary_offset;
	__u32 adapter_id;
};

struct kvm_irq_routing_hv_sint {
	__u32 vcpu;
	__u32 sint;
};


4.55 KVM_SET_TSC_KHZ

Capability: KVM_CAP_TSC_CONTROL
Architectures: x86
Type: vcpu ioctl
Parameters: virtual tsc_khz
Returns: 0 on success, -1 on error

Specifies the tsc frequency for the virtual machine. The unit of the
frequency is KHz.


4.56 KVM_GET_TSC_KHZ

Capability: KVM_CAP_GET_TSC_KHZ
Architectures: x86
Type: vcpu ioctl
Parameters: none
Returns: virtual tsc-khz on success, negative value on error

Returns the tsc frequency of the guest. The unit of the return value is
KHz. If the host has unstable tsc this ioctl returns -EIO instead as an
error.


4.57 KVM_GET_LAPIC

Capability: KVM_CAP_IRQCHIP
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_lapic_state (out)
Returns: 0 on success, -1 on error

#define KVM_APIC_REG_SIZE 0x400
struct kvm_lapic_state {
	char regs[KVM_APIC_REG_SIZE];
};

Reads the Local APIC registers and copies them into the input argument.  The
data format and layout are the same as documented in the architecture manual.

If KVM_X2APIC_API_USE_32BIT_IDS feature of KVM_CAP_X2APIC_API is
enabled, then the format of APIC_ID register depends on the APIC mode
(reported by MSR_IA32_APICBASE) of its VCPU.  x2APIC stores APIC ID in
the APIC_ID register (bytes 32-35).  xAPIC only allows an 8-bit APIC ID
which is stored in bits 31-24 of the APIC register, or equivalently in
byte 35 of struct kvm_lapic_state's regs field.  KVM_GET_LAPIC must then
be called after MSR_IA32_APICBASE has been set with KVM_SET_MSR.

If KVM_X2APIC_API_USE_32BIT_IDS feature is disabled, struct kvm_lapic_state
always uses xAPIC format.


4.58 KVM_SET_LAPIC

Capability: KVM_CAP_IRQCHIP
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_lapic_state (in)
Returns: 0 on success, -1 on error

#define KVM_APIC_REG_SIZE 0x400
struct kvm_lapic_state {
	char regs[KVM_APIC_REG_SIZE];
};

Copies the input argument into the Local APIC registers.  The data format
and layout are the same as documented in the architecture manual.

The format of the APIC ID register (bytes 32-35 of struct kvm_lapic_state's
regs field) depends on the state of the KVM_CAP_X2APIC_API capability.
See the note in KVM_GET_LAPIC.


4.59 KVM_IOEVENTFD

Capability: KVM_CAP_IOEVENTFD
Architectures: all
Type: vm ioctl
Parameters: struct kvm_ioeventfd (in)
Returns: 0 on success, !0 on error

This ioctl attaches or detaches an ioeventfd to a legal pio/mmio address
within the guest.  A guest write in the registered address will signal the
provided event instead of triggering an exit.

struct kvm_ioeventfd {
	__u64 datamatch;
	__u64 addr;        /* legal pio/mmio address */
	__u32 len;         /* 0, 1, 2, 4, or 8 bytes    */
	__s32 fd;
	__u32 flags;
	__u8  pad[36];
};

For the special case of virtio-ccw devices on s390, the ioevent is matched
to a subchannel/virtqueue tuple instead.

The following flags are defined:

#define KVM_IOEVENTFD_FLAG_DATAMATCH (1 << kvm_ioeventfd_flag_nr_datamatch)
#define KVM_IOEVENTFD_FLAG_PIO       (1 << kvm_ioeventfd_flag_nr_pio)
#define KVM_IOEVENTFD_FLAG_DEASSIGN  (1 << kvm_ioeventfd_flag_nr_deassign)
#define KVM_IOEVENTFD_FLAG_VIRTIO_CCW_NOTIFY \
	(1 << kvm_ioeventfd_flag_nr_virtio_ccw_notify)

If datamatch flag is set, the event will be signaled only if the written value
to the registered address is equal to datamatch in struct kvm_ioeventfd.

For virtio-ccw devices, addr contains the subchannel id and datamatch the
virtqueue index.

With KVM_CAP_IOEVENTFD_ANY_LENGTH, a zero length ioeventfd is allowed, and
the kernel will ignore the length of guest write and may get a faster vmexit.
The speedup may only apply to specific architectures, but the ioeventfd will
work anyway.

4.60 KVM_DIRTY_TLB

Capability: KVM_CAP_SW_TLB
Architectures: ppc
Type: vcpu ioctl
Parameters: struct kvm_dirty_tlb (in)
Returns: 0 on success, -1 on error

struct kvm_dirty_tlb {
	__u64 bitmap;
	__u32 num_dirty;
};

This must be called whenever userspace has changed an entry in the shared
TLB, prior to calling KVM_RUN on the associated vcpu.

The "bitmap" field is the userspace address of an array.  This array
consists of a number of bits, equal to the total number of TLB entries as
determined by the last successful call to KVM_CONFIG_TLB, rounded up to the
nearest multiple of 64.

Each bit corresponds to one TLB entry, ordered the same as in the shared TLB
array.

The array is little-endian: the bit 0 is the least significant bit of the
first byte, bit 8 is the least significant bit of the second byte, etc.
This avoids any complications with differing word sizes.

The "num_dirty" field is a performance hint for KVM to determine whether it
should skip processing the bitmap and just invalidate everything.  It must
be set to the number of set bits in the bitmap.


4.62 KVM_CREATE_SPAPR_TCE

Capability: KVM_CAP_SPAPR_TCE
Architectures: powerpc
Type: vm ioctl
Parameters: struct kvm_create_spapr_tce (in)
Returns: file descriptor for manipulating the created TCE table

This creates a virtual TCE (translation control entry) table, which
is an IOMMU for PAPR-style virtual I/O.  It is used to translate
logical addresses used in virtual I/O into guest physical addresses,
and provides a scatter/gather capability for PAPR virtual I/O.

/* for KVM_CAP_SPAPR_TCE */
struct kvm_create_spapr_tce {
	__u64 liobn;
	__u32 window_size;
};

The liobn field gives the logical IO bus number for which to create a
TCE table.  The window_size field specifies the size of the DMA window
which this TCE table will translate - the table will contain one 64
bit TCE entry for every 4kiB of the DMA window.

When the guest issues an H_PUT_TCE hcall on a liobn for which a TCE
table has been created using this ioctl(), the kernel will handle it
in real mode, updating the TCE table.  H_PUT_TCE calls for other
liobns will cause a vm exit and must be handled by userspace.

The return value is a file descriptor which can be passed to mmap(2)
to map the created TCE table into userspace.  This lets userspace read
the entries written by kernel-handled H_PUT_TCE calls, and also lets
userspace update the TCE table directly which is useful in some
circumstances.


4.63 KVM_ALLOCATE_RMA

Capability: KVM_CAP_PPC_RMA
Architectures: powerpc
Type: vm ioctl
Parameters: struct kvm_allocate_rma (out)
Returns: file descriptor for mapping the allocated RMA

This allocates a Real Mode Area (RMA) from the pool allocated at boot
time by the kernel.  An RMA is a physically-contiguous, aligned region
of memory used on older POWER processors to provide the memory which
will be accessed by real-mode (MMU off) accesses in a KVM guest.
POWER processors support a set of sizes for the RMA that usually
includes 64MB, 128MB, 256MB and some larger powers of two.

/* for KVM_ALLOCATE_RMA */
struct kvm_allocate_rma {
	__u64 rma_size;
};

The return value is a file descriptor which can be passed to mmap(2)
to map the allocated RMA into userspace.  The mapped area can then be
passed to the KVM_SET_USER_MEMORY_REGION ioctl to establish it as the
RMA for a virtual machine.  The size of the RMA in bytes (which is
fixed at host kernel boot time) is returned in the rma_size field of
the argument structure.

The KVM_CAP_PPC_RMA capability is 1 or 2 if the KVM_ALLOCATE_RMA ioctl
is supported; 2 if the processor requires all virtual machines to have
an RMA, or 1 if the processor can use an RMA but doesn't require it,
because it supports the Virtual RMA (VRMA) facility.


4.64 KVM_NMI

Capability: KVM_CAP_USER_NMI
Architectures: x86
Type: vcpu ioctl
Parameters: none
Returns: 0 on success, -1 on error

Queues an NMI on the thread's vcpu.  Note this is well defined only
when KVM_CREATE_IRQCHIP has not been called, since this is an interface
between the virtual cpu core and virtual local APIC.  After KVM_CREATE_IRQCHIP
has been called, this interface is completely emulated within the kernel.

To use this to emulate the LINT1 input with KVM_CREATE_IRQCHIP, use the
following algorithm:

  - pause the vcpu
  - read the local APIC's state (KVM_GET_LAPIC)
  - check whether changing LINT1 will queue an NMI (see the LVT entry for LINT1)
  - if so, issue KVM_NMI
  - resume the vcpu

Some guests configure the LINT1 NMI input to cause a panic, aiding in
debugging.


4.65 KVM_S390_UCAS_MAP

Capability: KVM_CAP_S390_UCONTROL
Architectures: s390
Type: vcpu ioctl
Parameters: struct kvm_s390_ucas_mapping (in)
Returns: 0 in case of success

The parameter is defined like this:
	struct kvm_s390_ucas_mapping {
		__u64 user_addr;
		__u64 vcpu_addr;
		__u64 length;
	};

This ioctl maps the memory at "user_addr" with the length "length" to
the vcpu's address space starting at "vcpu_addr". All parameters need to
be aligned by 1 megabyte.


4.66 KVM_S390_UCAS_UNMAP

Capability: KVM_CAP_S390_UCONTROL
Architectures: s390
Type: vcpu ioctl
Parameters: struct kvm_s390_ucas_mapping (in)
Returns: 0 in case of success

The parameter is defined like this:
	struct kvm_s390_ucas_mapping {
		__u64 user_addr;
		__u64 vcpu_addr;
		__u64 length;
	};

This ioctl unmaps the memory in the vcpu's address space starting at
"vcpu_addr" with the length "length". The field "user_addr" is ignored.
All parameters need to be aligned by 1 megabyte.


4.67 KVM_S390_VCPU_FAULT

Capability: KVM_CAP_S390_UCONTROL
Architectures: s390
Type: vcpu ioctl
Parameters: vcpu absolute address (in)
Returns: 0 in case of success

This call creates a page table entry on the virtual cpu's address space
(for user controlled virtual machines) or the virtual machine's address
space (for regular virtual machines). This only works for minor faults,
thus it's recommended to access subject memory page via the user page
table upfront. This is useful to handle validity intercepts for user
controlled virtual machines to fault in the virtual cpu's lowcore pages
prior to calling the KVM_RUN ioctl.


4.68 KVM_SET_ONE_REG

Capability: KVM_CAP_ONE_REG
Architectures: all
Type: vcpu ioctl
Parameters: struct kvm_one_reg (in)
Returns: 0 on success, negative value on failure
Errors:
  ENOENT:   no such register
  EINVAL:   invalid register ID, or no such register
  EPERM:    (arm64) register access not allowed before vcpu finalization
(These error codes are indicative only: do not rely on a specific error
code being returned in a specific situation.)

struct kvm_one_reg {
       __u64 id;
       __u64 addr;
};

Using this ioctl, a single vcpu register can be set to a specific value
defined by user space with the passed in struct kvm_one_reg, where id
refers to the register identifier as described below and addr is a pointer
to a variable with the respective size. There can be architecture agnostic
and architecture specific registers. Each have their own range of operation
and their own constants and width. To keep track of the implemented
registers, find a list below:

  Arch  |           Register            | Width (bits)
        |                               |
  PPC   | KVM_REG_PPC_HIOR              | 64
  PPC   | KVM_REG_PPC_IAC1              | 64
  PPC   | KVM_REG_PPC_IAC2              | 64
  PPC   | KVM_REG_PPC_IAC3              | 64
  PPC   | KVM_REG_PPC_IAC4              | 64
  PPC   | KVM_REG_PPC_DAC1              | 64
  PPC   | KVM_REG_PPC_DAC2              | 64
  PPC   | KVM_REG_PPC_DABR              | 64
  PPC   | KVM_REG_PPC_DSCR              | 64
  PPC   | KVM_REG_PPC_PURR              | 64
  PPC   | KVM_REG_PPC_SPURR             | 64
  PPC   | KVM_REG_PPC_DAR               | 64
  PPC   | KVM_REG_PPC_DSISR             | 32
  PPC   | KVM_REG_PPC_AMR               | 64
  PPC   | KVM_REG_PPC_UAMOR             | 64
  PPC   | KVM_REG_PPC_MMCR0             | 64
  PPC   | KVM_REG_PPC_MMCR1             | 64
  PPC   | KVM_REG_PPC_MMCRA             | 64
  PPC   | KVM_REG_PPC_MMCR2             | 64
  PPC   | KVM_REG_PPC_MMCRS             | 64
  PPC   | KVM_REG_PPC_SIAR              | 64
  PPC   | KVM_REG_PPC_SDAR              | 64
  PPC   | KVM_REG_PPC_SIER              | 64
  PPC   | KVM_REG_PPC_PMC1              | 32
  PPC   | KVM_REG_PPC_PMC2              | 32
  PPC   | KVM_REG_PPC_PMC3              | 32
  PPC   | KVM_REG_PPC_PMC4              | 32
  PPC   | KVM_REG_PPC_PMC5              | 32
  PPC   | KVM_REG_PPC_PMC6              | 32
  PPC   | KVM_REG_PPC_PMC7              | 32
  PPC   | KVM_REG_PPC_PMC8              | 32
  PPC   | KVM_REG_PPC_FPR0              | 64
          ...
  PPC   | KVM_REG_PPC_FPR31             | 64
  PPC   | KVM_REG_PPC_VR0               | 128
          ...
  PPC   | KVM_REG_PPC_VR31              | 128
  PPC   | KVM_REG_PPC_VSR0              | 128
          ...
  PPC   | KVM_REG_PPC_VSR31             | 128
  PPC   | KVM_REG_PPC_FPSCR             | 64
  PPC   | KVM_REG_PPC_VSCR              | 32
  PPC   | KVM_REG_PPC_VPA_ADDR          | 64
  PPC   | KVM_REG_PPC_VPA_SLB           | 128
  PPC   | KVM_REG_PPC_VPA_DTL           | 128
  PPC   | KVM_REG_PPC_EPCR              | 32
  PPC   | KVM_REG_PPC_EPR               | 32
  PPC   | KVM_REG_PPC_TCR               | 32
  PPC   | KVM_REG_PPC_TSR               | 32
  PPC   | KVM_REG_PPC_OR_TSR            | 32
  PPC   | KVM_REG_PPC_CLEAR_TSR         | 32
  PPC   | KVM_REG_PPC_MAS0              | 32
  PPC   | KVM_REG_PPC_MAS1              | 32
  PPC   | KVM_REG_PPC_MAS2              | 64
  PPC   | KVM_REG_PPC_MAS7_3            | 64
  PPC   | KVM_REG_PPC_MAS4              | 32
  PPC   | KVM_REG_PPC_MAS6              | 32
  PPC   | KVM_REG_PPC_MMUCFG            | 32
  PPC   | KVM_REG_PPC_TLB0CFG           | 32
  PPC   | KVM_REG_PPC_TLB1CFG           | 32
  PPC   | KVM_REG_PPC_TLB2CFG           | 32
  PPC   | KVM_REG_PPC_TLB3CFG           | 32
  PPC   | KVM_REG_PPC_TLB0PS            | 32
  PPC   | KVM_REG_PPC_TLB1PS            | 32
  PPC   | KVM_REG_PPC_TLB2PS            | 32
  PPC   | KVM_REG_PPC_TLB3PS            | 32
  PPC   | KVM_REG_PPC_EPTCFG            | 32
  PPC   | KVM_REG_PPC_ICP_STATE         | 64
  PPC   | KVM_REG_PPC_VP_STATE          | 128
  PPC   | KVM_REG_PPC_TB_OFFSET         | 64
  PPC   | KVM_REG_PPC_SPMC1             | 32
  PPC   | KVM_REG_PPC_SPMC2             | 32
  PPC   | KVM_REG_PPC_IAMR              | 64
  PPC   | KVM_REG_PPC_TFHAR             | 64
  PPC   | KVM_REG_PPC_TFIAR             | 64
  PPC   | KVM_REG_PPC_TEXASR            | 64
  PPC   | KVM_REG_PPC_FSCR              | 64
  PPC   | KVM_REG_PPC_PSPB              | 32
  PPC   | KVM_REG_PPC_EBBHR             | 64
  PPC   | KVM_REG_PPC_EBBRR             | 64
  PPC   | KVM_REG_PPC_BESCR             | 64
  PPC   | KVM_REG_PPC_TAR               | 64
  PPC   | KVM_REG_PPC_DPDES             | 64
  PPC   | KVM_REG_PPC_DAWR              | 64
  PPC   | KVM_REG_PPC_DAWRX             | 64
  PPC   | KVM_REG_PPC_CIABR             | 64
  PPC   | KVM_REG_PPC_IC                | 64
  PPC   | KVM_REG_PPC_VTB               | 64
  PPC   | KVM_REG_PPC_CSIGR             | 64
  PPC   | KVM_REG_PPC_TACR              | 64
  PPC   | KVM_REG_PPC_TCSCR             | 64
  PPC   | KVM_REG_PPC_PID               | 64
  PPC   | KVM_REG_PPC_ACOP              | 64
  PPC   | KVM_REG_PPC_VRSAVE            | 32
  PPC   | KVM_REG_PPC_LPCR              | 32
  PPC   | KVM_REG_PPC_LPCR_64           | 64
  PPC   | KVM_REG_PPC_PPR               | 64
  PPC   | KVM_REG_PPC_ARCH_COMPAT       | 32
  PPC   | KVM_REG_PPC_DABRX             | 32
  PPC   | KVM_REG_PPC_WORT              | 64
  PPC	| KVM_REG_PPC_SPRG9             | 64
  PPC	| KVM_REG_PPC_DBSR              | 32
  PPC   | KVM_REG_PPC_TIDR              | 64
  PPC   | KVM_REG_PPC_PSSCR             | 64
  PPC   | KVM_REG_PPC_DEC_EXPIRY        | 64
  PPC   | KVM_REG_PPC_PTCR              | 64
  PPC   | KVM_REG_PPC_TM_GPR0           | 64
          ...
  PPC   | KVM_REG_PPC_TM_GPR31          | 64
  PPC   | KVM_REG_PPC_TM_VSR0           | 128
          ...
  PPC   | KVM_REG_PPC_TM_VSR63          | 128
  PPC   | KVM_REG_PPC_TM_CR             | 64
  PPC   | KVM_REG_PPC_TM_LR             | 64
  PPC   | KVM_REG_PPC_TM_CTR            | 64
  PPC   | KVM_REG_PPC_TM_FPSCR          | 64
  PPC   | KVM_REG_PPC_TM_AMR            | 64
  PPC   | KVM_REG_PPC_TM_PPR            | 64
  PPC   | KVM_REG_PPC_TM_VRSAVE         | 64
  PPC   | KVM_REG_PPC_TM_VSCR           | 32
  PPC   | KVM_REG_PPC_TM_DSCR           | 64
  PPC   | KVM_REG_PPC_TM_TAR            | 64
  PPC   | KVM_REG_PPC_TM_XER            | 64
        |                               |
  MIPS  | KVM_REG_MIPS_R0               | 64
          ...
  MIPS  | KVM_REG_MIPS_R31              | 64
  MIPS  | KVM_REG_MIPS_HI               | 64
  MIPS  | KVM_REG_MIPS_LO               | 64
  MIPS  | KVM_REG_MIPS_PC               | 64
  MIPS  | KVM_REG_MIPS_CP0_INDEX        | 32
  MIPS  | KVM_REG_MIPS_CP0_ENTRYLO0     | 64
  MIPS  | KVM_REG_MIPS_CP0_ENTRYLO1     | 64
  MIPS  | KVM_REG_MIPS_CP0_CONTEXT      | 64
  MIPS  | KVM_REG_MIPS_CP0_CONTEXTCONFIG| 32
  MIPS  | KVM_REG_MIPS_CP0_USERLOCAL    | 64
  MIPS  | KVM_REG_MIPS_CP0_XCONTEXTCONFIG| 64
  MIPS  | KVM_REG_MIPS_CP0_PAGEMASK     | 32
  MIPS  | KVM_REG_MIPS_CP0_PAGEGRAIN    | 32
  MIPS  | KVM_REG_MIPS_CP0_SEGCTL0      | 64
  MIPS  | KVM_REG_MIPS_CP0_SEGCTL1      | 64
  MIPS  | KVM_REG_MIPS_CP0_SEGCTL2      | 64
  MIPS  | KVM_REG_MIPS_CP0_PWBASE       | 64
  MIPS  | KVM_REG_MIPS_CP0_PWFIELD      | 64
  MIPS  | KVM_REG_MIPS_CP0_PWSIZE       | 64
  MIPS  | KVM_REG_MIPS_CP0_WIRED        | 32
  MIPS  | KVM_REG_MIPS_CP0_PWCTL        | 32
  MIPS  | KVM_REG_MIPS_CP0_HWRENA       | 32
  MIPS  | KVM_REG_MIPS_CP0_BADVADDR     | 64
  MIPS  | KVM_REG_MIPS_CP0_BADINSTR     | 32
  MIPS  | KVM_REG_MIPS_CP0_BADINSTRP    | 32
  MIPS  | KVM_REG_MIPS_CP0_COUNT        | 32
  MIPS  | KVM_REG_MIPS_CP0_ENTRYHI      | 64
  MIPS  | KVM_REG_MIPS_CP0_COMPARE      | 32
  MIPS  | KVM_REG_MIPS_CP0_STATUS       | 32
  MIPS  | KVM_REG_MIPS_CP0_INTCTL       | 32
  MIPS  | KVM_REG_MIPS_CP0_CAUSE        | 32
  MIPS  | KVM_REG_MIPS_CP0_EPC          | 64
  MIPS  | KVM_REG_MIPS_CP0_PRID         | 32
  MIPS  | KVM_REG_MIPS_CP0_EBASE        | 64
  MIPS  | KVM_REG_MIPS_CP0_CONFIG       | 32
  MIPS  | KVM_REG_MIPS_CP0_CONFIG1      | 32
  MIPS  | KVM_REG_MIPS_CP0_CONFIG2      | 32
  MIPS  | KVM_REG_MIPS_CP0_CONFIG3      | 32
  MIPS  | KVM_REG_MIPS_CP0_CONFIG4      | 32
  MIPS  | KVM_REG_MIPS_CP0_CONFIG5      | 32
  MIPS  | KVM_REG_MIPS_CP0_CONFIG7      | 32
  MIPS  | KVM_REG_MIPS_CP0_XCONTEXT     | 64
  MIPS  | KVM_REG_MIPS_CP0_ERROREPC     | 64
  MIPS  | KVM_REG_MIPS_CP0_KSCRATCH1    | 64
  MIPS  | KVM_REG_MIPS_CP0_KSCRATCH2    | 64
  MIPS  | KVM_REG_MIPS_CP0_KSCRATCH3    | 64
  MIPS  | KVM_REG_MIPS_CP0_KSCRATCH4    | 64
  MIPS  | KVM_REG_MIPS_CP0_KSCRATCH5    | 64
  MIPS  | KVM_REG_MIPS_CP0_KSCRATCH6    | 64
  MIPS  | KVM_REG_MIPS_CP0_MAAR(0..63)  | 64
  MIPS  | KVM_REG_MIPS_COUNT_CTL        | 64
  MIPS  | KVM_REG_MIPS_COUNT_RESUME     | 64
  MIPS  | KVM_REG_MIPS_COUNT_HZ         | 64
  MIPS  | KVM_REG_MIPS_FPR_32(0..31)    | 32
  MIPS  | KVM_REG_MIPS_FPR_64(0..31)    | 64
  MIPS  | KVM_REG_MIPS_VEC_128(0..31)   | 128
  MIPS  | KVM_REG_MIPS_FCR_IR           | 32
  MIPS  | KVM_REG_MIPS_FCR_CSR          | 32
  MIPS  | KVM_REG_MIPS_MSA_IR           | 32
  MIPS  | KVM_REG_MIPS_MSA_CSR          | 32

ARM registers are mapped using the lower 32 bits.  The upper 16 of that
is the register group type, or coprocessor number:

ARM core registers have the following id bit patterns:
  0x4020 0000 0010 <index into the kvm_regs struct:16>

ARM 32-bit CP15 registers have the following id bit patterns:
  0x4020 0000 000F <zero:1> <crn:4> <crm:4> <opc1:4> <opc2:3>

ARM 64-bit CP15 registers have the following id bit patterns:
  0x4030 0000 000F <zero:1> <zero:4> <crm:4> <opc1:4> <zero:3>

ARM CCSIDR registers are demultiplexed by CSSELR value:
  0x4020 0000 0011 00 <csselr:8>

ARM 32-bit VFP control registers have the following id bit patterns:
  0x4020 0000 0012 1 <regno:12>

ARM 64-bit FP registers have the following id bit patterns:
  0x4030 0000 0012 0 <regno:12>

ARM firmware pseudo-registers have the following bit pattern:
  0x4030 0000 0014 <regno:16>


arm64 registers are mapped using the lower 32 bits. The upper 16 of
that is the register group type, or coprocessor number:

arm64 core/FP-SIMD registers have the following id bit patterns. Note
that the size of the access is variable, as the kvm_regs structure
contains elements ranging from 32 to 128 bits. The index is a 32bit
value in the kvm_regs structure seen as a 32bit array.
  0x60x0 0000 0010 <index into the kvm_regs struct:16>

Specifically:
    Encoding            Register  Bits  kvm_regs member
----------------------------------------------------------------
  0x6030 0000 0010 0000 X0          64  regs.regs[0]
  0x6030 0000 0010 0002 X1          64  regs.regs[1]
    ...
  0x6030 0000 0010 003c X30         64  regs.regs[30]
  0x6030 0000 0010 003e SP          64  regs.sp
  0x6030 0000 0010 0040 PC          64  regs.pc
  0x6030 0000 0010 0042 PSTATE      64  regs.pstate
  0x6030 0000 0010 0044 SP_EL1      64  sp_el1
  0x6030 0000 0010 0046 ELR_EL1     64  elr_el1
  0x6030 0000 0010 0048 SPSR_EL1    64  spsr[KVM_SPSR_EL1] (alias SPSR_SVC)
  0x6030 0000 0010 004a SPSR_ABT    64  spsr[KVM_SPSR_ABT]
  0x6030 0000 0010 004c SPSR_UND    64  spsr[KVM_SPSR_UND]
  0x6030 0000 0010 004e SPSR_IRQ    64  spsr[KVM_SPSR_IRQ]
  0x6060 0000 0010 0050 SPSR_FIQ    64  spsr[KVM_SPSR_FIQ]
  0x6040 0000 0010 0054 V0         128  fp_regs.vregs[0]    (*)
  0x6040 0000 0010 0058 V1         128  fp_regs.vregs[1]    (*)
    ...
  0x6040 0000 0010 00d0 V31        128  fp_regs.vregs[31]   (*)
  0x6020 0000 0010 00d4 FPSR        32  fp_regs.fpsr
  0x6020 0000 0010 00d5 FPCR        32  fp_regs.fpcr

(*) These encodings are not accepted for SVE-enabled vcpus.  See
    KVM_ARM_VCPU_INIT.

    The equivalent register content can be accessed via bits [127:0] of
    the corresponding SVE Zn registers instead for vcpus that have SVE
    enabled (see below).

arm64 CCSIDR registers are demultiplexed by CSSELR value:
  0x6020 0000 0011 00 <csselr:8>

arm64 system registers have the following id bit patterns:
  0x6030 0000 0013 <op0:2> <op1:3> <crn:4> <crm:4> <op2:3>

arm64 firmware pseudo-registers have the following bit pattern:
  0x6030 0000 0014 <regno:16>

arm64 SVE registers have the following bit patterns:
  0x6080 0000 0015 00 <n:5> <slice:5>   Zn bits[2048*slice + 2047 : 2048*slice]
  0x6050 0000 0015 04 <n:4> <slice:5>   Pn bits[256*slice + 255 : 256*slice]
  0x6050 0000 0015 060 <slice:5>        FFR bits[256*slice + 255 : 256*slice]
  0x6060 0000 0015 ffff                 KVM_REG_ARM64_SVE_VLS pseudo-register

Access to register IDs where 2048 * slice >= 128 * max_vq will fail with
ENOENT.  max_vq is the vcpu's maximum supported vector length in 128-bit
quadwords: see (**) below.

These registers are only accessible on vcpus for which SVE is enabled.
See KVM_ARM_VCPU_INIT for details.

In addition, except for KVM_REG_ARM64_SVE_VLS, these registers are not
accessible until the vcpu's SVE configuration has been finalized
using KVM_ARM_VCPU_FINALIZE(KVM_ARM_VCPU_SVE).  See KVM_ARM_VCPU_INIT
and KVM_ARM_VCPU_FINALIZE for more information about this procedure.

KVM_REG_ARM64_SVE_VLS is a pseudo-register that allows the set of vector
lengths supported by the vcpu to be discovered and configured by
userspace.  When transferred to or from user memory via KVM_GET_ONE_REG
or KVM_SET_ONE_REG, the value of this register is of type
__u64[KVM_ARM64_SVE_VLS_WORDS], and encodes the set of vector lengths as
follows:

__u64 vector_lengths[KVM_ARM64_SVE_VLS_WORDS];

if (vq >= SVE_VQ_MIN && vq <= SVE_VQ_MAX &&
    ((vector_lengths[(vq - KVM_ARM64_SVE_VQ_MIN) / 64] >>
		((vq - KVM_ARM64_SVE_VQ_MIN) % 64)) & 1))
	/* Vector length vq * 16 bytes supported */
else
	/* Vector length vq * 16 bytes not supported */

(**) The maximum value vq for which the above condition is true is
max_vq.  This is the maximum vector length available to the guest on
this vcpu, and determines which register slices are visible through
this ioctl interface.

(See Documentation/arm64/sve.rst for an explanation of the "vq"
nomenclature.)

KVM_REG_ARM64_SVE_VLS is only accessible after KVM_ARM_VCPU_INIT.
KVM_ARM_VCPU_INIT initialises it to the best set of vector lengths that
the host supports.

Userspace may subsequently modify it if desired until the vcpu's SVE
configuration is finalized using KVM_ARM_VCPU_FINALIZE(KVM_ARM_VCPU_SVE).

Apart from simply removing all vector lengths from the host set that
exceed some value, support for arbitrarily chosen sets of vector lengths
is hardware-dependent and may not be available.  Attempting to configure
an invalid set of vector lengths via KVM_SET_ONE_REG will fail with
EINVAL.

After the vcpu's SVE configuration is finalized, further attempts to
write this register will fail with EPERM.


MIPS registers are mapped using the lower 32 bits.  The upper 16 of that is
the register group type:

MIPS core registers (see above) have the following id bit patterns:
  0x7030 0000 0000 <reg:16>

MIPS CP0 registers (see KVM_REG_MIPS_CP0_* above) have the following id bit
patterns depending on whether they're 32-bit or 64-bit registers:
  0x7020 0000 0001 00 <reg:5> <sel:3>   (32-bit)
  0x7030 0000 0001 00 <reg:5> <sel:3>   (64-bit)

Note: KVM_REG_MIPS_CP0_ENTRYLO0 and KVM_REG_MIPS_CP0_ENTRYLO1 are the MIPS64
versions of the EntryLo registers regardless of the word size of the host
hardware, host kernel, guest, and whether XPA is present in the guest, i.e.
with the RI and XI bits (if they exist) in bits 63 and 62 respectively, and
the PFNX field starting at bit 30.

MIPS MAARs (see KVM_REG_MIPS_CP0_MAAR(*) above) have the following id bit
patterns:
  0x7030 0000 0001 01 <reg:8>

MIPS KVM control registers (see above) have the following id bit patterns:
  0x7030 0000 0002 <reg:16>

MIPS FPU registers (see KVM_REG_MIPS_FPR_{32,64}() above) have the following
id bit patterns depending on the size of the register being accessed. They are
always accessed according to the current guest FPU mode (Status.FR and
Config5.FRE), i.e. as the guest would see them, and they become unpredictable
if the guest FPU mode is changed. MIPS SIMD Architecture (MSA) vector
registers (see KVM_REG_MIPS_VEC_128() above) have similar patterns as they
overlap the FPU registers:
  0x7020 0000 0003 00 <0:3> <reg:5> (32-bit FPU registers)
  0x7030 0000 0003 00 <0:3> <reg:5> (64-bit FPU registers)
  0x7040 0000 0003 00 <0:3> <reg:5> (128-bit MSA vector registers)

MIPS FPU control registers (see KVM_REG_MIPS_FCR_{IR,CSR} above) have the
following id bit patterns:
  0x7020 0000 0003 01 <0:3> <reg:5>

MIPS MSA control registers (see KVM_REG_MIPS_MSA_{IR,CSR} above) have the
following id bit patterns:
  0x7020 0000 0003 02 <0:3> <reg:5>


4.69 KVM_GET_ONE_REG

Capability: KVM_CAP_ONE_REG
Architectures: all
Type: vcpu ioctl
Parameters: struct kvm_one_reg (in and out)
Returns: 0 on success, negative value on failure
Errors include:
  ENOENT:   no such register
  EINVAL:   invalid register ID, or no such register
  EPERM:    (arm64) register access not allowed before vcpu finalization
(These error codes are indicative only: do not rely on a specific error
code being returned in a specific situation.)

This ioctl allows to receive the value of a single register implemented
in a vcpu. The register to read is indicated by the "id" field of the
kvm_one_reg struct passed in. On success, the register value can be found
at the memory location pointed to by "addr".

The list of registers accessible using this interface is identical to the
list in 4.68.


4.70 KVM_KVMCLOCK_CTRL

Capability: KVM_CAP_KVMCLOCK_CTRL
Architectures: Any that implement pvclocks (currently x86 only)
Type: vcpu ioctl
Parameters: None
Returns: 0 on success, -1 on error

This signals to the host kernel that the specified guest is being paused by
userspace.  The host will set a flag in the pvclock structure that is checked
from the soft lockup watchdog.  The flag is part of the pvclock structure that
is shared between guest and host, specifically the second bit of the flags
field of the pvclock_vcpu_time_info structure.  It will be set exclusively by
the host and read/cleared exclusively by the guest.  The guest operation of
checking and clearing the flag must an atomic operation so
load-link/store-conditional, or equivalent must be used.  There are two cases
where the guest will clear the flag: when the soft lockup watchdog timer resets
itself or when a soft lockup is detected.  This ioctl can be called any time
after pausing the vcpu, but before it is resumed.


4.71 KVM_SIGNAL_MSI

Capability: KVM_CAP_SIGNAL_MSI
Architectures: x86 arm arm64
Type: vm ioctl
Parameters: struct kvm_msi (in)
Returns: >0 on delivery, 0 if guest blocked the MSI, and -1 on error

Directly inject a MSI message. Only valid with in-kernel irqchip that handles
MSI messages.

struct kvm_msi {
	__u32 address_lo;
	__u32 address_hi;
	__u32 data;
	__u32 flags;
	__u32 devid;
	__u8  pad[12];
};

flags: KVM_MSI_VALID_DEVID: devid contains a valid value.  The per-VM
  KVM_CAP_MSI_DEVID capability advertises the requirement to provide
  the device ID.  If this capability is not available, userspace
  should never set the KVM_MSI_VALID_DEVID flag as the ioctl might fail.

If KVM_MSI_VALID_DEVID is set, devid contains a unique device identifier
for the device that wrote the MSI message.  For PCI, this is usually a
BFD identifier in the lower 16 bits.

On x86, address_hi is ignored unless the KVM_X2APIC_API_USE_32BIT_IDS
feature of KVM_CAP_X2APIC_API capability is enabled.  If it is enabled,
address_hi bits 31-8 provide bits 31-8 of the destination id.  Bits 7-0 of
address_hi must be zero.


4.71 KVM_CREATE_PIT2

Capability: KVM_CAP_PIT2
Architectures: x86
Type: vm ioctl
Parameters: struct kvm_pit_config (in)
Returns: 0 on success, -1 on error

Creates an in-kernel device model for the i8254 PIT. This call is only valid
after enabling in-kernel irqchip support via KVM_CREATE_IRQCHIP. The following
parameters have to be passed:

struct kvm_pit_config {
	__u32 flags;
	__u32 pad[15];
};

Valid flags are:

#define KVM_PIT_SPEAKER_DUMMY     1 /* emulate speaker port stub */

PIT timer interrupts may use a per-VM kernel thread for injection. If it
exists, this thread will have a name of the following pattern:

kvm-pit/<owner-process-pid>

When running a guest with elevated priorities, the scheduling parameters of
this thread may have to be adjusted accordingly.

This IOCTL replaces the obsolete KVM_CREATE_PIT.


4.72 KVM_GET_PIT2

Capability: KVM_CAP_PIT_STATE2
Architectures: x86
Type: vm ioctl
Parameters: struct kvm_pit_state2 (out)
Returns: 0 on success, -1 on error

Retrieves the state of the in-kernel PIT model. Only valid after
KVM_CREATE_PIT2. The state is returned in the following structure:

struct kvm_pit_state2 {
	struct kvm_pit_channel_state channels[3];
	__u32 flags;
	__u32 reserved[9];
};

Valid flags are:

/* disable PIT in HPET legacy mode */
#define KVM_PIT_FLAGS_HPET_LEGACY  0x00000001

This IOCTL replaces the obsolete KVM_GET_PIT.


4.73 KVM_SET_PIT2

Capability: KVM_CAP_PIT_STATE2
Architectures: x86
Type: vm ioctl
Parameters: struct kvm_pit_state2 (in)
Returns: 0 on success, -1 on error

Sets the state of the in-kernel PIT model. Only valid after KVM_CREATE_PIT2.
See KVM_GET_PIT2 for details on struct kvm_pit_state2.

This IOCTL replaces the obsolete KVM_SET_PIT.


4.74 KVM_PPC_GET_SMMU_INFO

Capability: KVM_CAP_PPC_GET_SMMU_INFO
Architectures: powerpc
Type: vm ioctl
Parameters: None
Returns: 0 on success, -1 on error

This populates and returns a structure describing the features of
the "Server" class MMU emulation supported by KVM.
This can in turn be used by userspace to generate the appropriate
device-tree properties for the guest operating system.

The structure contains some global information, followed by an
array of supported segment page sizes:

      struct kvm_ppc_smmu_info {
	     __u64 flags;
	     __u32 slb_size;
	     __u32 pad;
	     struct kvm_ppc_one_seg_page_size sps[KVM_PPC_PAGE_SIZES_MAX_SZ];
      };

The supported flags are:

    - KVM_PPC_PAGE_SIZES_REAL:
        When that flag is set, guest page sizes must "fit" the backing
        store page sizes. When not set, any page size in the list can
        be used regardless of how they are backed by userspace.

    - KVM_PPC_1T_SEGMENTS
        The emulated MMU supports 1T segments in addition to the
        standard 256M ones.

    - KVM_PPC_NO_HASH
	This flag indicates that HPT guests are not supported by KVM,
	thus all guests must use radix MMU mode.

The "slb_size" field indicates how many SLB entries are supported

The "sps" array contains 8 entries indicating the supported base
page sizes for a segment in increasing order. Each entry is defined
as follow:

   struct kvm_ppc_one_seg_page_size {
	__u32 page_shift;	/* Base page shift of segment (or 0) */
	__u32 slb_enc;		/* SLB encoding for BookS */
	struct kvm_ppc_one_page_size enc[KVM_PPC_PAGE_SIZES_MAX_SZ];
   };

An entry with a "page_shift" of 0 is unused. Because the array is
organized in increasing order, a lookup can stop when encoutering
such an entry.

The "slb_enc" field provides the encoding to use in the SLB for the
page size. The bits are in positions such as the value can directly
be OR'ed into the "vsid" argument of the slbmte instruction.

The "enc" array is a list which for each of those segment base page
size provides the list of supported actual page sizes (which can be
only larger or equal to the base page size), along with the
corresponding encoding in the hash PTE. Similarly, the array is
8 entries sorted by increasing sizes and an entry with a "0" shift
is an empty entry and a terminator:

   struct kvm_ppc_one_page_size {
	__u32 page_shift;	/* Page shift (or 0) */
	__u32 pte_enc;		/* Encoding in the HPTE (>>12) */
   };

The "pte_enc" field provides a value that can OR'ed into the hash
PTE's RPN field (ie, it needs to be shifted left by 12 to OR it
into the hash PTE second double word).

4.75 KVM_IRQFD

Capability: KVM_CAP_IRQFD
Architectures: x86 s390 arm arm64
Type: vm ioctl
Parameters: struct kvm_irqfd (in)
Returns: 0 on success, -1 on error

Allows setting an eventfd to directly trigger a guest interrupt.
kvm_irqfd.fd specifies the file descriptor to use as the eventfd and
kvm_irqfd.gsi specifies the irqchip pin toggled by this event.  When
an event is triggered on the eventfd, an interrupt is injected into
the guest using the specified gsi pin.  The irqfd is removed using
the KVM_IRQFD_FLAG_DEASSIGN flag, specifying both kvm_irqfd.fd
and kvm_irqfd.gsi.

With KVM_CAP_IRQFD_RESAMPLE, KVM_IRQFD supports a de-assert and notify
mechanism allowing emulation of level-triggered, irqfd-based
interrupts.  When KVM_IRQFD_FLAG_RESAMPLE is set the user must pass an
additional eventfd in the kvm_irqfd.resamplefd field.  When operating
in resample mode, posting of an interrupt through kvm_irq.fd asserts
the specified gsi in the irqchip.  When the irqchip is resampled, such
as from an EOI, the gsi is de-asserted and the user is notified via
kvm_irqfd.resamplefd.  It is the user's responsibility to re-queue
the interrupt if the device making use of it still requires service.
Note that closing the resamplefd is not sufficient to disable the
irqfd.  The KVM_IRQFD_FLAG_RESAMPLE is only necessary on assignment
and need not be specified with KVM_IRQFD_FLAG_DEASSIGN.

On arm/arm64, gsi routing being supported, the following can happen:
- in case no routing entry is associated to this gsi, injection fails
- in case the gsi is associated to an irqchip routing entry,
  irqchip.pin + 32 corresponds to the injected SPI ID.
- in case the gsi is associated to an MSI routing entry, the MSI
  message and device ID are translated into an LPI (support restricted
  to GICv3 ITS in-kernel emulation).

4.76 KVM_PPC_ALLOCATE_HTAB

Capability: KVM_CAP_PPC_ALLOC_HTAB
Architectures: powerpc
Type: vm ioctl
Parameters: Pointer to u32 containing hash table order (in/out)
Returns: 0 on success, -1 on error

This requests the host kernel to allocate an MMU hash table for a
guest using the PAPR paravirtualization interface.  This only does
anything if the kernel is configured to use the Book 3S HV style of
virtualization.  Otherwise the capability doesn't exist and the ioctl
returns an ENOTTY error.  The rest of this description assumes Book 3S
HV.

There must be no vcpus running when this ioctl is called; if there
are, it will do nothing and return an EBUSY error.

The parameter is a pointer to a 32-bit unsigned integer variable
containing the order (log base 2) of the desired size of the hash
table, which must be between 18 and 46.  On successful return from the
ioctl, the value will not be changed by the kernel.

If no hash table has been allocated when any vcpu is asked to run
(with the KVM_RUN ioctl), the host kernel will allocate a
default-sized hash table (16 MB).

If this ioctl is called when a hash table has already been allocated,
with a different order from the existing hash table, the existing hash
table will be freed and a new one allocated.  If this is ioctl is
called when a hash table has already been allocated of the same order
as specified, the kernel will clear out the existing hash table (zero
all HPTEs).  In either case, if the guest is using the virtualized
real-mode area (VRMA) facility, the kernel will re-create the VMRA
HPTEs on the next KVM_RUN of any vcpu.

4.77 KVM_S390_INTERRUPT

Capability: basic
Architectures: s390
Type: vm ioctl, vcpu ioctl
Parameters: struct kvm_s390_interrupt (in)
Returns: 0 on success, -1 on error

Allows to inject an interrupt to the guest. Interrupts can be floating
(vm ioctl) or per cpu (vcpu ioctl), depending on the interrupt type.

Interrupt parameters are passed via kvm_s390_interrupt:

struct kvm_s390_interrupt {
	__u32 type;
	__u32 parm;
	__u64 parm64;
};

type can be one of the following:

KVM_S390_SIGP_STOP (vcpu) - sigp stop; optional flags in parm
KVM_S390_PROGRAM_INT (vcpu) - program check; code in parm
KVM_S390_SIGP_SET_PREFIX (vcpu) - sigp set prefix; prefix address in parm
KVM_S390_RESTART (vcpu) - restart
KVM_S390_INT_CLOCK_COMP (vcpu) - clock comparator interrupt
KVM_S390_INT_CPU_TIMER (vcpu) - CPU timer interrupt
KVM_S390_INT_VIRTIO (vm) - virtio external interrupt; external interrupt
			   parameters in parm and parm64
KVM_S390_INT_SERVICE (vm) - sclp external interrupt; sclp parameter in parm
KVM_S390_INT_EMERGENCY (vcpu) - sigp emergency; source cpu in parm
KVM_S390_INT_EXTERNAL_CALL (vcpu) - sigp external call; source cpu in parm
KVM_S390_INT_IO(ai,cssid,ssid,schid) (vm) - compound value to indicate an
    I/O interrupt (ai - adapter interrupt; cssid,ssid,schid - subchannel);
    I/O interruption parameters in parm (subchannel) and parm64 (intparm,
    interruption subclass)
KVM_S390_MCHK (vm, vcpu) - machine check interrupt; cr 14 bits in parm,
                           machine check interrupt code in parm64 (note that
                           machine checks needing further payload are not
                           supported by this ioctl)

This is an asynchronous vcpu ioctl and can be invoked from any thread.

4.78 KVM_PPC_GET_HTAB_FD

Capability: KVM_CAP_PPC_HTAB_FD
Architectures: powerpc
Type: vm ioctl
Parameters: Pointer to struct kvm_get_htab_fd (in)
Returns: file descriptor number (>= 0) on success, -1 on error

This returns a file descriptor that can be used either to read out the
entries in the guest's hashed page table (HPT), or to write entries to
initialize the HPT.  The returned fd can only be written to if the
KVM_GET_HTAB_WRITE bit is set in the flags field of the argument, and
can only be read if that bit is clear.  The argument struct looks like
this:

/* For KVM_PPC_GET_HTAB_FD */
struct kvm_get_htab_fd {
	__u64	flags;
	__u64	start_index;
	__u64	reserved[2];
};

/* Values for kvm_get_htab_fd.flags */
#define KVM_GET_HTAB_BOLTED_ONLY	((__u64)0x1)
#define KVM_GET_HTAB_WRITE		((__u64)0x2)

The `start_index' field gives the index in the HPT of the entry at
which to start reading.  It is ignored when writing.

Reads on the fd will initially supply information about all
"interesting" HPT entries.  Interesting entries are those with the
bolted bit set, if the KVM_GET_HTAB_BOLTED_ONLY bit is set, otherwise
all entries.  When the end of the HPT is reached, the read() will
return.  If read() is called again on the fd, it will start again from
the beginning of the HPT, but will only return HPT entries that have
changed since they were last read.

Data read or written is structured as a header (8 bytes) followed by a
series of valid HPT entries (16 bytes) each.  The header indicates how
many valid HPT entries there are and how many invalid entries follow
the valid entries.  The invalid entries are not represented explicitly
in the stream.  The header format is:

struct kvm_get_htab_header {
	__u32	index;
	__u16	n_valid;
	__u16	n_invalid;
};

Writes to the fd create HPT entries starting at the index given in the
header; first `n_valid' valid entries with contents from the data
written, then `n_invalid' invalid entries, invalidating any previously
valid entries found.

4.79 KVM_CREATE_DEVICE

Capability: KVM_CAP_DEVICE_CTRL
Type: vm ioctl
Parameters: struct kvm_create_device (in/out)
Returns: 0 on success, -1 on error
Errors:
  ENODEV: The device type is unknown or unsupported
  EEXIST: Device already created, and this type of device may not
          be instantiated multiple times

  Other error conditions may be defined by individual device types or
  have their standard meanings.

Creates an emulated device in the kernel.  The file descriptor returned
in fd can be used with KVM_SET/GET/HAS_DEVICE_ATTR.

If the KVM_CREATE_DEVICE_TEST flag is set, only test whether the
device type is supported (not necessarily whether it can be created
in the current vm).

Individual devices should not define flags.  Attributes should be used
for specifying any behavior that is not implied by the device type
number.

struct kvm_create_device {
	__u32	type;	/* in: KVM_DEV_TYPE_xxx */
	__u32	fd;	/* out: device handle */
	__u32	flags;	/* in: KVM_CREATE_DEVICE_xxx */
};

4.80 KVM_SET_DEVICE_ATTR/KVM_GET_DEVICE_ATTR

Capability: KVM_CAP_DEVICE_CTRL, KVM_CAP_VM_ATTRIBUTES for vm device,
  KVM_CAP_VCPU_ATTRIBUTES for vcpu device
Type: device ioctl, vm ioctl, vcpu ioctl
Parameters: struct kvm_device_attr
Returns: 0 on success, -1 on error
Errors:
  ENXIO:  The group or attribute is unknown/unsupported for this device
          or hardware support is missing.
  EPERM:  The attribute cannot (currently) be accessed this way
          (e.g. read-only attribute, or attribute that only makes
          sense when the device is in a different state)

  Other error conditions may be defined by individual device types.

Gets/sets a specified piece of device configuration and/or state.  The
semantics are device-specific.  See individual device documentation in
the "devices" directory.  As with ONE_REG, the size of the data
transferred is defined by the particular attribute.

struct kvm_device_attr {
	__u32	flags;		/* no flags currently defined */
	__u32	group;		/* device-defined */
	__u64	attr;		/* group-defined */
	__u64	addr;		/* userspace address of attr data */
};

4.81 KVM_HAS_DEVICE_ATTR

Capability: KVM_CAP_DEVICE_CTRL, KVM_CAP_VM_ATTRIBUTES for vm device,
  KVM_CAP_VCPU_ATTRIBUTES for vcpu device
Type: device ioctl, vm ioctl, vcpu ioctl
Parameters: struct kvm_device_attr
Returns: 0 on success, -1 on error
Errors:
  ENXIO:  The group or attribute is unknown/unsupported for this device
          or hardware support is missing.

Tests whether a device supports a particular attribute.  A successful
return indicates the attribute is implemented.  It does not necessarily
indicate that the attribute can be read or written in the device's
current state.  "addr" is ignored.

4.82 KVM_ARM_VCPU_INIT

Capability: basic
Architectures: arm, arm64
Type: vcpu ioctl
Parameters: struct kvm_vcpu_init (in)
Returns: 0 on success; -1 on error
Errors:
  EINVAL:    the target is unknown, or the combination of features is invalid.
  ENOENT:    a features bit specified is unknown.

This tells KVM what type of CPU to present to the guest, and what
optional features it should have.  This will cause a reset of the cpu
registers to their initial values.  If this is not called, KVM_RUN will
return ENOEXEC for that vcpu.

Note that because some registers reflect machine topology, all vcpus
should be created before this ioctl is invoked.

Userspace can call this function multiple times for a given vcpu, including
after the vcpu has been run. This will reset the vcpu to its initial
state. All calls to this function after the initial call must use the same
target and same set of feature flags, otherwise EINVAL will be returned.

Possible features:
	- KVM_ARM_VCPU_POWER_OFF: Starts the CPU in a power-off state.
	  Depends on KVM_CAP_ARM_PSCI.  If not set, the CPU will be powered on
	  and execute guest code when KVM_RUN is called.
	- KVM_ARM_VCPU_EL1_32BIT: Starts the CPU in a 32bit mode.
	  Depends on KVM_CAP_ARM_EL1_32BIT (arm64 only).
	- KVM_ARM_VCPU_PSCI_0_2: Emulate PSCI v0.2 (or a future revision
          backward compatible with v0.2) for the CPU.
	  Depends on KVM_CAP_ARM_PSCI_0_2.
	- KVM_ARM_VCPU_PMU_V3: Emulate PMUv3 for the CPU.
	  Depends on KVM_CAP_ARM_PMU_V3.

	- KVM_ARM_VCPU_PTRAUTH_ADDRESS: Enables Address Pointer authentication
	  for arm64 only.
	  Depends on KVM_CAP_ARM_PTRAUTH_ADDRESS.
	  If KVM_CAP_ARM_PTRAUTH_ADDRESS and KVM_CAP_ARM_PTRAUTH_GENERIC are
	  both present, then both KVM_ARM_VCPU_PTRAUTH_ADDRESS and
	  KVM_ARM_VCPU_PTRAUTH_GENERIC must be requested or neither must be
	  requested.

	- KVM_ARM_VCPU_PTRAUTH_GENERIC: Enables Generic Pointer authentication
	  for arm64 only.
	  Depends on KVM_CAP_ARM_PTRAUTH_GENERIC.
	  If KVM_CAP_ARM_PTRAUTH_ADDRESS and KVM_CAP_ARM_PTRAUTH_GENERIC are
	  both present, then both KVM_ARM_VCPU_PTRAUTH_ADDRESS and
	  KVM_ARM_VCPU_PTRAUTH_GENERIC must be requested or neither must be
	  requested.

	- KVM_ARM_VCPU_SVE: Enables SVE for the CPU (arm64 only).
	  Depends on KVM_CAP_ARM_SVE.
	  Requires KVM_ARM_VCPU_FINALIZE(KVM_ARM_VCPU_SVE):

	   * After KVM_ARM_VCPU_INIT:

	      - KVM_REG_ARM64_SVE_VLS may be read using KVM_GET_ONE_REG: the
	        initial value of this pseudo-register indicates the best set of
	        vector lengths possible for a vcpu on this host.

	   * Before KVM_ARM_VCPU_FINALIZE(KVM_ARM_VCPU_SVE):

	      - KVM_RUN and KVM_GET_REG_LIST are not available;

	      - KVM_GET_ONE_REG and KVM_SET_ONE_REG cannot be used to access
	        the scalable archietctural SVE registers
	        KVM_REG_ARM64_SVE_ZREG(), KVM_REG_ARM64_SVE_PREG() or
	        KVM_REG_ARM64_SVE_FFR;

	      - KVM_REG_ARM64_SVE_VLS may optionally be written using
	        KVM_SET_ONE_REG, to modify the set of vector lengths available
	        for the vcpu.

	   * After KVM_ARM_VCPU_FINALIZE(KVM_ARM_VCPU_SVE):

	      - the KVM_REG_ARM64_SVE_VLS pseudo-register is immutable, and can
	        no longer be written using KVM_SET_ONE_REG.

4.83 KVM_ARM_PREFERRED_TARGET

Capability: basic
Architectures: arm, arm64
Type: vm ioctl
Parameters: struct struct kvm_vcpu_init (out)
Returns: 0 on success; -1 on error
Errors:
  ENODEV:    no preferred target available for the host

This queries KVM for preferred CPU target type which can be emulated
by KVM on underlying host.

The ioctl returns struct kvm_vcpu_init instance containing information
about preferred CPU target type and recommended features for it.  The
kvm_vcpu_init->features bitmap returned will have feature bits set if
the preferred target recommends setting these features, but this is
not mandatory.

The information returned by this ioctl can be used to prepare an instance
of struct kvm_vcpu_init for KVM_ARM_VCPU_INIT ioctl which will result in
in VCPU matching underlying host.


4.84 KVM_GET_REG_LIST

Capability: basic
Architectures: arm, arm64, mips
Type: vcpu ioctl
Parameters: struct kvm_reg_list (in/out)
Returns: 0 on success; -1 on error
Errors:
  E2BIG:     the reg index list is too big to fit in the array specified by
             the user (the number required will be written into n).

struct kvm_reg_list {
	__u64 n; /* number of registers in reg[] */
	__u64 reg[0];
};

This ioctl returns the guest registers that are supported for the
KVM_GET_ONE_REG/KVM_SET_ONE_REG calls.


4.85 KVM_ARM_SET_DEVICE_ADDR (deprecated)

Capability: KVM_CAP_ARM_SET_DEVICE_ADDR
Architectures: arm, arm64
Type: vm ioctl
Parameters: struct kvm_arm_device_address (in)
Returns: 0 on success, -1 on error
Errors:
  ENODEV: The device id is unknown
  ENXIO:  Device not supported on current system
  EEXIST: Address already set
  E2BIG:  Address outside guest physical address space
  EBUSY:  Address overlaps with other device range

struct kvm_arm_device_addr {
	__u64 id;
	__u64 addr;
};

Specify a device address in the guest's physical address space where guests
can access emulated or directly exposed devices, which the host kernel needs
to know about. The id field is an architecture specific identifier for a
specific device.

ARM/arm64 divides the id field into two parts, a device id and an
address type id specific to the individual device.

  bits:  | 63        ...       32 | 31    ...    16 | 15    ...    0 |
  field: |        0x00000000      |     device id   |  addr type id  |

ARM/arm64 currently only require this when using the in-kernel GIC
support for the hardware VGIC features, using KVM_ARM_DEVICE_VGIC_V2
as the device id.  When setting the base address for the guest's
mapping of the VGIC virtual CPU and distributor interface, the ioctl
must be called after calling KVM_CREATE_IRQCHIP, but before calling
KVM_RUN on any of the VCPUs.  Calling this ioctl twice for any of the
base addresses will return -EEXIST.

Note, this IOCTL is deprecated and the more flexible SET/GET_DEVICE_ATTR API
should be used instead.


4.86 KVM_PPC_RTAS_DEFINE_TOKEN

Capability: KVM_CAP_PPC_RTAS
Architectures: ppc
Type: vm ioctl
Parameters: struct kvm_rtas_token_args
Returns: 0 on success, -1 on error

Defines a token value for a RTAS (Run Time Abstraction Services)
service in order to allow it to be handled in the kernel.  The
argument struct gives the name of the service, which must be the name
of a service that has a kernel-side implementation.  If the token
value is non-zero, it will be associated with that service, and
subsequent RTAS calls by the guest specifying that token will be
handled by the kernel.  If the token value is 0, then any token
associated with the service will be forgotten, and subsequent RTAS
calls by the guest for that service will be passed to userspace to be
handled.

4.87 KVM_SET_GUEST_DEBUG

Capability: KVM_CAP_SET_GUEST_DEBUG
Architectures: x86, s390, ppc, arm64
Type: vcpu ioctl
Parameters: struct kvm_guest_debug (in)
Returns: 0 on success; -1 on error

struct kvm_guest_debug {
       __u32 control;
       __u32 pad;
       struct kvm_guest_debug_arch arch;
};

Set up the processor specific debug registers and configure vcpu for
handling guest debug events. There are two parts to the structure, the
first a control bitfield indicates the type of debug events to handle
when running. Common control bits are:

  - KVM_GUESTDBG_ENABLE:        guest debugging is enabled
  - KVM_GUESTDBG_SINGLESTEP:    the next run should single-step

The top 16 bits of the control field are architecture specific control
flags which can include the following:

  - KVM_GUESTDBG_USE_SW_BP:     using software breakpoints [x86, arm64]
  - KVM_GUESTDBG_USE_HW_BP:     using hardware breakpoints [x86, s390, arm64]
  - KVM_GUESTDBG_INJECT_DB:     inject DB type exception [x86]
  - KVM_GUESTDBG_INJECT_BP:     inject BP type exception [x86]
  - KVM_GUESTDBG_EXIT_PENDING:  trigger an immediate guest exit [s390]

For example KVM_GUESTDBG_USE_SW_BP indicates that software breakpoints
are enabled in memory so we need to ensure breakpoint exceptions are
correctly trapped and the KVM run loop exits at the breakpoint and not
running off into the normal guest vector. For KVM_GUESTDBG_USE_HW_BP
we need to ensure the guest vCPUs architecture specific registers are
updated to the correct (supplied) values.

The second part of the structure is architecture specific and
typically contains a set of debug registers.

For arm64 the number of debug registers is implementation defined and
can be determined by querying the KVM_CAP_GUEST_DEBUG_HW_BPS and
KVM_CAP_GUEST_DEBUG_HW_WPS capabilities which return a positive number
indicating the number of supported registers.

When debug events exit the main run loop with the reason
KVM_EXIT_DEBUG with the kvm_debug_exit_arch part of the kvm_run
structure containing architecture specific debug information.

4.88 KVM_GET_EMULATED_CPUID

Capability: KVM_CAP_EXT_EMUL_CPUID
Architectures: x86
Type: system ioctl
Parameters: struct kvm_cpuid2 (in/out)
Returns: 0 on success, -1 on error

struct kvm_cpuid2 {
	__u32 nent;
	__u32 flags;
	struct kvm_cpuid_entry2 entries[0];
};

The member 'flags' is used for passing flags from userspace.

#define KVM_CPUID_FLAG_SIGNIFCANT_INDEX		BIT(0)
#define KVM_CPUID_FLAG_STATEFUL_FUNC		BIT(1)
#define KVM_CPUID_FLAG_STATE_READ_NEXT		BIT(2)

struct kvm_cpuid_entry2 {
	__u32 function;
	__u32 index;
	__u32 flags;
	__u32 eax;
	__u32 ebx;
	__u32 ecx;
	__u32 edx;
	__u32 padding[3];
};

This ioctl returns x86 cpuid features which are emulated by
kvm.Userspace can use the information returned by this ioctl to query
which features are emulated by kvm instead of being present natively.

Userspace invokes KVM_GET_EMULATED_CPUID by passing a kvm_cpuid2
structure with the 'nent' field indicating the number of entries in
the variable-size array 'entries'. If the number of entries is too low
to describe the cpu capabilities, an error (E2BIG) is returned. If the
number is too high, the 'nent' field is adjusted and an error (ENOMEM)
is returned. If the number is just right, the 'nent' field is adjusted
to the number of valid entries in the 'entries' array, which is then
filled.

The entries returned are the set CPUID bits of the respective features
which kvm emulates, as returned by the CPUID instruction, with unknown
or unsupported feature bits cleared.

Features like x2apic, for example, may not be present in the host cpu
but are exposed by kvm in KVM_GET_SUPPORTED_CPUID because they can be
emulated efficiently and thus not included here.

The fields in each entry are defined as follows:

  function: the eax value used to obtain the entry
  index: the ecx value used to obtain the entry (for entries that are
         affected by ecx)
  flags: an OR of zero or more of the following:
        KVM_CPUID_FLAG_SIGNIFCANT_INDEX:
           if the index field is valid
        KVM_CPUID_FLAG_STATEFUL_FUNC:
           if cpuid for this function returns different values for successive
           invocations; there will be several entries with the same function,
           all with this flag set
        KVM_CPUID_FLAG_STATE_READ_NEXT:
           for KVM_CPUID_FLAG_STATEFUL_FUNC entries, set if this entry is
           the first entry to be read by a cpu
   eax, ebx, ecx, edx: the values returned by the cpuid instruction for
         this function/index combination

4.89 KVM_S390_MEM_OP

Capability: KVM_CAP_S390_MEM_OP
Architectures: s390
Type: vcpu ioctl
Parameters: struct kvm_s390_mem_op (in)
Returns: = 0 on success,
         < 0 on generic error (e.g. -EFAULT or -ENOMEM),
         > 0 if an exception occurred while walking the page tables

Read or write data from/to the logical (virtual) memory of a VCPU.

Parameters are specified via the following structure:

struct kvm_s390_mem_op {
	__u64 gaddr;		/* the guest address */
	__u64 flags;		/* flags */
	__u32 size;		/* amount of bytes */
	__u32 op;		/* type of operation */
	__u64 buf;		/* buffer in userspace */
	__u8 ar;		/* the access register number */
	__u8 reserved[31];	/* should be set to 0 */
};

The type of operation is specified in the "op" field. It is either
KVM_S390_MEMOP_LOGICAL_READ for reading from logical memory space or
KVM_S390_MEMOP_LOGICAL_WRITE for writing to logical memory space. The
KVM_S390_MEMOP_F_CHECK_ONLY flag can be set in the "flags" field to check
whether the corresponding memory access would create an access exception
(without touching the data in the memory at the destination). In case an
access exception occurred while walking the MMU tables of the guest, the
ioctl returns a positive error number to indicate the type of exception.
This exception is also raised directly at the corresponding VCPU if the
flag KVM_S390_MEMOP_F_INJECT_EXCEPTION is set in the "flags" field.

The start address of the memory region has to be specified in the "gaddr"
field, and the length of the region in the "size" field (which must not
be 0). The maximum value for "size" can be obtained by checking the
KVM_CAP_S390_MEM_OP capability. "buf" is the buffer supplied by the
userspace application where the read data should be written to for
KVM_S390_MEMOP_LOGICAL_READ, or where the data that should be written is
stored for a KVM_S390_MEMOP_LOGICAL_WRITE. When KVM_S390_MEMOP_F_CHECK_ONLY
is specified, "buf" is unused and can be NULL. "ar" designates the access
register number to be used; the valid range is 0..15.

The "reserved" field is meant for future extensions. It is not used by
KVM with the currently defined set of flags.

4.90 KVM_S390_GET_SKEYS

Capability: KVM_CAP_S390_SKEYS
Architectures: s390
Type: vm ioctl
Parameters: struct kvm_s390_skeys
Returns: 0 on success, KVM_S390_GET_KEYS_NONE if guest is not using storage
         keys, negative value on error

This ioctl is used to get guest storage key values on the s390
architecture. The ioctl takes parameters via the kvm_s390_skeys struct.

struct kvm_s390_skeys {
	__u64 start_gfn;
	__u64 count;
	__u64 skeydata_addr;
	__u32 flags;
	__u32 reserved[9];
};

The start_gfn field is the number of the first guest frame whose storage keys
you want to get.

The count field is the number of consecutive frames (starting from start_gfn)
whose storage keys to get. The count field must be at least 1 and the maximum
allowed value is defined as KVM_S390_SKEYS_ALLOC_MAX. Values outside this range
will cause the ioctl to return -EINVAL.

The skeydata_addr field is the address to a buffer large enough to hold count
bytes. This buffer will be filled with storage key data by the ioctl.

4.91 KVM_S390_SET_SKEYS

Capability: KVM_CAP_S390_SKEYS
Architectures: s390
Type: vm ioctl
Parameters: struct kvm_s390_skeys
Returns: 0 on success, negative value on error

This ioctl is used to set guest storage key values on the s390
architecture. The ioctl takes parameters via the kvm_s390_skeys struct.
See section on KVM_S390_GET_SKEYS for struct definition.

The start_gfn field is the number of the first guest frame whose storage keys
you want to set.

The count field is the number of consecutive frames (starting from start_gfn)
whose storage keys to get. The count field must be at least 1 and the maximum
allowed value is defined as KVM_S390_SKEYS_ALLOC_MAX. Values outside this range
will cause the ioctl to return -EINVAL.

The skeydata_addr field is the address to a buffer containing count bytes of
storage keys. Each byte in the buffer will be set as the storage key for a
single frame starting at start_gfn for count frames.

Note: If any architecturally invalid key value is found in the given data then
the ioctl will return -EINVAL.

4.92 KVM_S390_IRQ

Capability: KVM_CAP_S390_INJECT_IRQ
Architectures: s390
Type: vcpu ioctl
Parameters: struct kvm_s390_irq (in)
Returns: 0 on success, -1 on error
Errors:
  EINVAL: interrupt type is invalid
          type is KVM_S390_SIGP_STOP and flag parameter is invalid value
          type is KVM_S390_INT_EXTERNAL_CALL and code is bigger
            than the maximum of VCPUs
  EBUSY:  type is KVM_S390_SIGP_SET_PREFIX and vcpu is not stopped
          type is KVM_S390_SIGP_STOP and a stop irq is already pending
          type is KVM_S390_INT_EXTERNAL_CALL and an external call interrupt
            is already pending

Allows to inject an interrupt to the guest.

Using struct kvm_s390_irq as a parameter allows
to inject additional payload which is not
possible via KVM_S390_INTERRUPT.

Interrupt parameters are passed via kvm_s390_irq:

struct kvm_s390_irq {
	__u64 type;
	union {
		struct kvm_s390_io_info io;
		struct kvm_s390_ext_info ext;
		struct kvm_s390_pgm_info pgm;
		struct kvm_s390_emerg_info emerg;
		struct kvm_s390_extcall_info extcall;
		struct kvm_s390_prefix_info prefix;
		struct kvm_s390_stop_info stop;
		struct kvm_s390_mchk_info mchk;
		char reserved[64];
	} u;
};

type can be one of the following:

KVM_S390_SIGP_STOP - sigp stop; parameter in .stop
KVM_S390_PROGRAM_INT - program check; parameters in .pgm
KVM_S390_SIGP_SET_PREFIX - sigp set prefix; parameters in .prefix
KVM_S390_RESTART - restart; no parameters
KVM_S390_INT_CLOCK_COMP - clock comparator interrupt; no parameters
KVM_S390_INT_CPU_TIMER - CPU timer interrupt; no parameters
KVM_S390_INT_EMERGENCY - sigp emergency; parameters in .emerg
KVM_S390_INT_EXTERNAL_CALL - sigp external call; parameters in .extcall
KVM_S390_MCHK - machine check interrupt; parameters in .mchk

This is an asynchronous vcpu ioctl and can be invoked from any thread.

4.94 KVM_S390_GET_IRQ_STATE

Capability: KVM_CAP_S390_IRQ_STATE
Architectures: s390
Type: vcpu ioctl
Parameters: struct kvm_s390_irq_state (out)
Returns: >= number of bytes copied into buffer,
         -EINVAL if buffer size is 0,
         -ENOBUFS if buffer size is too small to fit all pending interrupts,
         -EFAULT if the buffer address was invalid

This ioctl allows userspace to retrieve the complete state of all currently
pending interrupts in a single buffer. Use cases include migration
and introspection. The parameter structure contains the address of a
userspace buffer and its length:

struct kvm_s390_irq_state {
	__u64 buf;
	__u32 flags;        /* will stay unused for compatibility reasons */
	__u32 len;
	__u32 reserved[4];  /* will stay unused for compatibility reasons */
};

Userspace passes in the above struct and for each pending interrupt a
struct kvm_s390_irq is copied to the provided buffer.

The structure contains a flags and a reserved field for future extensions. As
the kernel never checked for flags == 0 and QEMU never pre-zeroed flags and
reserved, these fields can not be used in the future without breaking
compatibility.

If -ENOBUFS is returned the buffer provided was too small and userspace
may retry with a bigger buffer.

4.95 KVM_S390_SET_IRQ_STATE

Capability: KVM_CAP_S390_IRQ_STATE
Architectures: s390
Type: vcpu ioctl
Parameters: struct kvm_s390_irq_state (in)
Returns: 0 on success,
         -EFAULT if the buffer address was invalid,
         -EINVAL for an invalid buffer length (see below),
         -EBUSY if there were already interrupts pending,
         errors occurring when actually injecting the
          interrupt. See KVM_S390_IRQ.

This ioctl allows userspace to set the complete state of all cpu-local
interrupts currently pending for the vcpu. It is intended for restoring
interrupt state after a migration. The input parameter is a userspace buffer
containing a struct kvm_s390_irq_state:

struct kvm_s390_irq_state {
	__u64 buf;
	__u32 flags;        /* will stay unused for compatibility reasons */
	__u32 len;
	__u32 reserved[4];  /* will stay unused for compatibility reasons */
};

The restrictions for flags and reserved apply as well.
(see KVM_S390_GET_IRQ_STATE)

The userspace memory referenced by buf contains a struct kvm_s390_irq
for each interrupt to be injected into the guest.
If one of the interrupts could not be injected for some reason the
ioctl aborts.

len must be a multiple of sizeof(struct kvm_s390_irq). It must be > 0
and it must not exceed (max_vcpus + 32) * sizeof(struct kvm_s390_irq),
which is the maximum number of possibly pending cpu-local interrupts.

4.96 KVM_SMI

Capability: KVM_CAP_X86_SMM
Architectures: x86
Type: vcpu ioctl
Parameters: none
Returns: 0 on success, -1 on error

Queues an SMI on the thread's vcpu.

4.97 KVM_CAP_PPC_MULTITCE

Capability: KVM_CAP_PPC_MULTITCE
Architectures: ppc
Type: vm

This capability means the kernel is capable of handling hypercalls
H_PUT_TCE_INDIRECT and H_STUFF_TCE without passing those into the user
space. This significantly accelerates DMA operations for PPC KVM guests.
User space should expect that its handlers for these hypercalls
are not going to be called if user space previously registered LIOBN
in KVM (via KVM_CREATE_SPAPR_TCE or similar calls).

In order to enable H_PUT_TCE_INDIRECT and H_STUFF_TCE use in the guest,
user space might have to advertise it for the guest. For example,
IBM pSeries (sPAPR) guest starts using them if "hcall-multi-tce" is
present in the "ibm,hypertas-functions" device-tree property.

The hypercalls mentioned above may or may not be processed successfully
in the kernel based fast path. If they can not be handled by the kernel,
they will get passed on to user space. So user space still has to have
an implementation for these despite the in kernel acceleration.

This capability is always enabled.

4.98 KVM_CREATE_SPAPR_TCE_64

Capability: KVM_CAP_SPAPR_TCE_64
Architectures: powerpc
Type: vm ioctl
Parameters: struct kvm_create_spapr_tce_64 (in)
Returns: file descriptor for manipulating the created TCE table

This is an extension for KVM_CAP_SPAPR_TCE which only supports 32bit
windows, described in 4.62 KVM_CREATE_SPAPR_TCE

This capability uses extended struct in ioctl interface:

/* for KVM_CAP_SPAPR_TCE_64 */
struct kvm_create_spapr_tce_64 {
	__u64 liobn;
	__u32 page_shift;
	__u32 flags;
	__u64 offset;	/* in pages */
	__u64 size; 	/* in pages */
};

The aim of extension is to support an additional bigger DMA window with
a variable page size.
KVM_CREATE_SPAPR_TCE_64 receives a 64bit window size, an IOMMU page shift and
a bus offset of the corresponding DMA window, @size and @offset are numbers
of IOMMU pages.

@flags are not used at the moment.

The rest of functionality is identical to KVM_CREATE_SPAPR_TCE.

4.99 KVM_REINJECT_CONTROL

Capability: KVM_CAP_REINJECT_CONTROL
Architectures: x86
Type: vm ioctl
Parameters: struct kvm_reinject_control (in)
Returns: 0 on success,
         -EFAULT if struct kvm_reinject_control cannot be read,
         -ENXIO if KVM_CREATE_PIT or KVM_CREATE_PIT2 didn't succeed earlier.

i8254 (PIT) has two modes, reinject and !reinject.  The default is reinject,
where KVM queues elapsed i8254 ticks and monitors completion of interrupt from
vector(s) that i8254 injects.  Reinject mode dequeues a tick and injects its
interrupt whenever there isn't a pending interrupt from i8254.
!reinject mode injects an interrupt as soon as a tick arrives.

struct kvm_reinject_control {
	__u8 pit_reinject;
	__u8 reserved[31];
};

pit_reinject = 0 (!reinject mode) is recommended, unless running an old
operating system that uses the PIT for timing (e.g. Linux 2.4.x).

4.100 KVM_PPC_CONFIGURE_V3_MMU

Capability: KVM_CAP_PPC_RADIX_MMU or KVM_CAP_PPC_HASH_MMU_V3
Architectures: ppc
Type: vm ioctl
Parameters: struct kvm_ppc_mmuv3_cfg (in)
Returns: 0 on success,
         -EFAULT if struct kvm_ppc_mmuv3_cfg cannot be read,
         -EINVAL if the configuration is invalid

This ioctl controls whether the guest will use radix or HPT (hashed
page table) translation, and sets the pointer to the process table for
the guest.

struct kvm_ppc_mmuv3_cfg {
	__u64	flags;
	__u64	process_table;
};

There are two bits that can be set in flags; KVM_PPC_MMUV3_RADIX and
KVM_PPC_MMUV3_GTSE.  KVM_PPC_MMUV3_RADIX, if set, configures the guest
to use radix tree translation, and if clear, to use HPT translation.
KVM_PPC_MMUV3_GTSE, if set and if KVM permits it, configures the guest
to be able to use the global TLB and SLB invalidation instructions;
if clear, the guest may not use these instructions.

The process_table field specifies the address and size of the guest
process table, which is in the guest's space.  This field is formatted
as the second doubleword of the partition table entry, as defined in
the Power ISA V3.00, Book III section 5.7.6.1.

4.101 KVM_PPC_GET_RMMU_INFO

Capability: KVM_CAP_PPC_RADIX_MMU
Architectures: ppc
Type: vm ioctl
Parameters: struct kvm_ppc_rmmu_info (out)
Returns: 0 on success,
	 -EFAULT if struct kvm_ppc_rmmu_info cannot be written,
	 -EINVAL if no useful information can be returned

This ioctl returns a structure containing two things: (a) a list
containing supported radix tree geometries, and (b) a list that maps
page sizes to put in the "AP" (actual page size) field for the tlbie
(TLB invalidate entry) instruction.

struct kvm_ppc_rmmu_info {
	struct kvm_ppc_radix_geom {
		__u8	page_shift;
		__u8	level_bits[4];
		__u8	pad[3];
	}	geometries[8];
	__u32	ap_encodings[8];
};

The geometries[] field gives up to 8 supported geometries for the
radix page table, in terms of the log base 2 of the smallest page
size, and the number of bits indexed at each level of the tree, from
the PTE level up to the PGD level in that order.  Any unused entries
will have 0 in the page_shift field.

The ap_encodings gives the supported page sizes and their AP field
encodings, encoded with the AP value in the top 3 bits and the log
base 2 of the page size in the bottom 6 bits.

4.102 KVM_PPC_RESIZE_HPT_PREPARE

Capability: KVM_CAP_SPAPR_RESIZE_HPT
Architectures: powerpc
Type: vm ioctl
Parameters: struct kvm_ppc_resize_hpt (in)
Returns: 0 on successful completion,
	 >0 if a new HPT is being prepared, the value is an estimated
             number of milliseconds until preparation is complete
         -EFAULT if struct kvm_reinject_control cannot be read,
	 -EINVAL if the supplied shift or flags are invalid
	 -ENOMEM if unable to allocate the new HPT
	 -ENOSPC if there was a hash collision when moving existing
                  HPT entries to the new HPT
	 -EIO on other error conditions

Used to implement the PAPR extension for runtime resizing of a guest's
Hashed Page Table (HPT).  Specifically this starts, stops or monitors
the preparation of a new potential HPT for the guest, essentially
implementing the H_RESIZE_HPT_PREPARE hypercall.

If called with shift > 0 when there is no pending HPT for the guest,
this begins preparation of a new pending HPT of size 2^(shift) bytes.
It then returns a positive integer with the estimated number of
milliseconds until preparation is complete.

If called when there is a pending HPT whose size does not match that
requested in the parameters, discards the existing pending HPT and
creates a new one as above.

If called when there is a pending HPT of the size requested, will:
  * If preparation of the pending HPT is already complete, return 0
  * If preparation of the pending HPT has failed, return an error
    code, then discard the pending HPT.
  * If preparation of the pending HPT is still in progress, return an
    estimated number of milliseconds until preparation is complete.

If called with shift == 0, discards any currently pending HPT and
returns 0 (i.e. cancels any in-progress preparation).

flags is reserved for future expansion, currently setting any bits in
flags will result in an -EINVAL.

Normally this will be called repeatedly with the same parameters until
it returns <= 0.  The first call will initiate preparation, subsequent
ones will monitor preparation until it completes or fails.

struct kvm_ppc_resize_hpt {
	__u64 flags;
	__u32 shift;
	__u32 pad;
};

4.103 KVM_PPC_RESIZE_HPT_COMMIT

Capability: KVM_CAP_SPAPR_RESIZE_HPT
Architectures: powerpc
Type: vm ioctl
Parameters: struct kvm_ppc_resize_hpt (in)
Returns: 0 on successful completion,
         -EFAULT if struct kvm_reinject_control cannot be read,
	 -EINVAL if the supplied shift or flags are invalid
	 -ENXIO is there is no pending HPT, or the pending HPT doesn't
                 have the requested size
	 -EBUSY if the pending HPT is not fully prepared
	 -ENOSPC if there was a hash collision when moving existing
                  HPT entries to the new HPT
	 -EIO on other error conditions

Used to implement the PAPR extension for runtime resizing of a guest's
Hashed Page Table (HPT).  Specifically this requests that the guest be
transferred to working with the new HPT, essentially implementing the
H_RESIZE_HPT_COMMIT hypercall.

This should only be called after KVM_PPC_RESIZE_HPT_PREPARE has
returned 0 with the same parameters.  In other cases
KVM_PPC_RESIZE_HPT_COMMIT will return an error (usually -ENXIO or
-EBUSY, though others may be possible if the preparation was started,
but failed).

This will have undefined effects on the guest if it has not already
placed itself in a quiescent state where no vcpu will make MMU enabled
memory accesses.

On succsful completion, the pending HPT will become the guest's active
HPT and the previous HPT will be discarded.

On failure, the guest will still be operating on its previous HPT.

struct kvm_ppc_resize_hpt {
	__u64 flags;
	__u32 shift;
	__u32 pad;
};

4.104 KVM_X86_GET_MCE_CAP_SUPPORTED

Capability: KVM_CAP_MCE
Architectures: x86
Type: system ioctl
Parameters: u64 mce_cap (out)
Returns: 0 on success, -1 on error

Returns supported MCE capabilities. The u64 mce_cap parameter
has the same format as the MSR_IA32_MCG_CAP register. Supported
capabilities will have the corresponding bits set.

4.105 KVM_X86_SETUP_MCE

Capability: KVM_CAP_MCE
Architectures: x86
Type: vcpu ioctl
Parameters: u64 mcg_cap (in)
Returns: 0 on success,
         -EFAULT if u64 mcg_cap cannot be read,
         -EINVAL if the requested number of banks is invalid,
         -EINVAL if requested MCE capability is not supported.

Initializes MCE support for use. The u64 mcg_cap parameter
has the same format as the MSR_IA32_MCG_CAP register and
specifies which capabilities should be enabled. The maximum
supported number of error-reporting banks can be retrieved when
checking for KVM_CAP_MCE. The supported capabilities can be
retrieved with KVM_X86_GET_MCE_CAP_SUPPORTED.

4.106 KVM_X86_SET_MCE

Capability: KVM_CAP_MCE
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_x86_mce (in)
Returns: 0 on success,
         -EFAULT if struct kvm_x86_mce cannot be read,
         -EINVAL if the bank number is invalid,
         -EINVAL if VAL bit is not set in status field.

Inject a machine check error (MCE) into the guest. The input
parameter is:

struct kvm_x86_mce {
	__u64 status;
	__u64 addr;
	__u64 misc;
	__u64 mcg_status;
	__u8 bank;
	__u8 pad1[7];
	__u64 pad2[3];
};

If the MCE being reported is an uncorrected error, KVM will
inject it as an MCE exception into the guest. If the guest
MCG_STATUS register reports that an MCE is in progress, KVM
causes an KVM_EXIT_SHUTDOWN vmexit.

Otherwise, if the MCE is a corrected error, KVM will just
store it in the corresponding bank (provided this bank is
not holding a previously reported uncorrected error).

4.107 KVM_S390_GET_CMMA_BITS

Capability: KVM_CAP_S390_CMMA_MIGRATION
Architectures: s390
Type: vm ioctl
Parameters: struct kvm_s390_cmma_log (in, out)
Returns: 0 on success, a negative value on error

This ioctl is used to get the values of the CMMA bits on the s390
architecture. It is meant to be used in two scenarios:
- During live migration to save the CMMA values. Live migration needs
  to be enabled via the KVM_REQ_START_MIGRATION VM property.
- To non-destructively peek at the CMMA values, with the flag
  KVM_S390_CMMA_PEEK set.

The ioctl takes parameters via the kvm_s390_cmma_log struct. The desired
values are written to a buffer whose location is indicated via the "values"
member in the kvm_s390_cmma_log struct.  The values in the input struct are
also updated as needed.
Each CMMA value takes up one byte.

struct kvm_s390_cmma_log {
	__u64 start_gfn;
	__u32 count;
	__u32 flags;
	union {
		__u64 remaining;
		__u64 mask;
	};
	__u64 values;
};

start_gfn is the number of the first guest frame whose CMMA values are
to be retrieved,

count is the length of the buffer in bytes,

values points to the buffer where the result will be written to.

If count is greater than KVM_S390_SKEYS_MAX, then it is considered to be
KVM_S390_SKEYS_MAX. KVM_S390_SKEYS_MAX is re-used for consistency with
other ioctls.

The result is written in the buffer pointed to by the field values, and
the values of the input parameter are updated as follows.

Depending on the flags, different actions are performed. The only
supported flag so far is KVM_S390_CMMA_PEEK.

The default behaviour if KVM_S390_CMMA_PEEK is not set is:
start_gfn will indicate the first page frame whose CMMA bits were dirty.
It is not necessarily the same as the one passed as input, as clean pages
are skipped.

count will indicate the number of bytes actually written in the buffer.
It can (and very often will) be smaller than the input value, since the
buffer is only filled until 16 bytes of clean values are found (which
are then not copied in the buffer). Since a CMMA migration block needs
the base address and the length, for a total of 16 bytes, we will send
back some clean data if there is some dirty data afterwards, as long as
the size of the clean data does not exceed the size of the header. This
allows to minimize the amount of data to be saved or transferred over
the network at the expense of more roundtrips to userspace. The next
invocation of the ioctl will skip over all the clean values, saving
potentially more than just the 16 bytes we found.

If KVM_S390_CMMA_PEEK is set:
the existing storage attributes are read even when not in migration
mode, and no other action is performed;

the output start_gfn will be equal to the input start_gfn,

the output count will be equal to the input count, except if the end of
memory has been reached.

In both cases:
the field "remaining" will indicate the total number of dirty CMMA values
still remaining, or 0 if KVM_S390_CMMA_PEEK is set and migration mode is
not enabled.

mask is unused.

values points to the userspace buffer where the result will be stored.

This ioctl can fail with -ENOMEM if not enough memory can be allocated to
complete the task, with -ENXIO if CMMA is not enabled, with -EINVAL if
KVM_S390_CMMA_PEEK is not set but migration mode was not enabled, with
-EFAULT if the userspace address is invalid or if no page table is
present for the addresses (e.g. when using hugepages).

4.108 KVM_S390_SET_CMMA_BITS

Capability: KVM_CAP_S390_CMMA_MIGRATION
Architectures: s390
Type: vm ioctl
Parameters: struct kvm_s390_cmma_log (in)
Returns: 0 on success, a negative value on error

This ioctl is used to set the values of the CMMA bits on the s390
architecture. It is meant to be used during live migration to restore
the CMMA values, but there are no restrictions on its use.
The ioctl takes parameters via the kvm_s390_cmma_values struct.
Each CMMA value takes up one byte.

struct kvm_s390_cmma_log {
	__u64 start_gfn;
	__u32 count;
	__u32 flags;
	union {
		__u64 remaining;
		__u64 mask;
	};
	__u64 values;
};

start_gfn indicates the starting guest frame number,

count indicates how many values are to be considered in the buffer,

flags is not used and must be 0.

mask indicates which PGSTE bits are to be considered.

remaining is not used.

values points to the buffer in userspace where to store the values.

This ioctl can fail with -ENOMEM if not enough memory can be allocated to
complete the task, with -ENXIO if CMMA is not enabled, with -EINVAL if
the count field is too large (e.g. more than KVM_S390_CMMA_SIZE_MAX) or
if the flags field was not 0, with -EFAULT if the userspace address is
invalid, if invalid pages are written to (e.g. after the end of memory)
or if no page table is present for the addresses (e.g. when using
hugepages).

4.109 KVM_PPC_GET_CPU_CHAR

Capability: KVM_CAP_PPC_GET_CPU_CHAR
Architectures: powerpc
Type: vm ioctl
Parameters: struct kvm_ppc_cpu_char (out)
Returns: 0 on successful completion
	 -EFAULT if struct kvm_ppc_cpu_char cannot be written

This ioctl gives userspace information about certain characteristics
of the CPU relating to speculative execution of instructions and
possible information leakage resulting from speculative execution (see
CVE-2017-5715, CVE-2017-5753 and CVE-2017-5754).  The information is
returned in struct kvm_ppc_cpu_char, which looks like this:

struct kvm_ppc_cpu_char {
	__u64	character;		/* characteristics of the CPU */
	__u64	behaviour;		/* recommended software behaviour */
	__u64	character_mask;		/* valid bits in character */
	__u64	behaviour_mask;		/* valid bits in behaviour */
};

For extensibility, the character_mask and behaviour_mask fields
indicate which bits of character and behaviour have been filled in by
the kernel.  If the set of defined bits is extended in future then
userspace will be able to tell whether it is running on a kernel that
knows about the new bits.

The character field describes attributes of the CPU which can help
with preventing inadvertent information disclosure - specifically,
whether there is an instruction to flash-invalidate the L1 data cache
(ori 30,30,0 or mtspr SPRN_TRIG2,rN), whether the L1 data cache is set
to a mode where entries can only be used by the thread that created
them, whether the bcctr[l] instruction prevents speculation, and
whether a speculation barrier instruction (ori 31,31,0) is provided.

The behaviour field describes actions that software should take to
prevent inadvertent information disclosure, and thus describes which
vulnerabilities the hardware is subject to; specifically whether the
L1 data cache should be flushed when returning to user mode from the
kernel, and whether a speculation barrier should be placed between an
array bounds check and the array access.

These fields use the same bit definitions as the new
H_GET_CPU_CHARACTERISTICS hypercall.

4.110 KVM_MEMORY_ENCRYPT_OP

Capability: basic
Architectures: x86
Type: system
Parameters: an opaque platform specific structure (in/out)
Returns: 0 on success; -1 on error

If the platform supports creating encrypted VMs then this ioctl can be used
for issuing platform-specific memory encryption commands to manage those
encrypted VMs.

Currently, this ioctl is used for issuing Secure Encrypted Virtualization
(SEV) commands on AMD Processors. The SEV commands are defined in
Documentation/virt/kvm/amd-memory-encryption.rst.

4.111 KVM_MEMORY_ENCRYPT_REG_REGION

Capability: basic
Architectures: x86
Type: system
Parameters: struct kvm_enc_region (in)
Returns: 0 on success; -1 on error

This ioctl can be used to register a guest memory region which may
contain encrypted data (e.g. guest RAM, SMRAM etc).

It is used in the SEV-enabled guest. When encryption is enabled, a guest
memory region may contain encrypted data. The SEV memory encryption
engine uses a tweak such that two identical plaintext pages, each at
different locations will have differing ciphertexts. So swapping or
moving ciphertext of those pages will not result in plaintext being
swapped. So relocating (or migrating) physical backing pages for the SEV
guest will require some additional steps.

Note: The current SEV key management spec does not provide commands to
swap or migrate (move) ciphertext pages. Hence, for now we pin the guest
memory region registered with the ioctl.

4.112 KVM_MEMORY_ENCRYPT_UNREG_REGION

Capability: basic
Architectures: x86
Type: system
Parameters: struct kvm_enc_region (in)
Returns: 0 on success; -1 on error

This ioctl can be used to unregister the guest memory region registered
with KVM_MEMORY_ENCRYPT_REG_REGION ioctl above.

4.113 KVM_HYPERV_EVENTFD

Capability: KVM_CAP_HYPERV_EVENTFD
Architectures: x86
Type: vm ioctl
Parameters: struct kvm_hyperv_eventfd (in)

This ioctl (un)registers an eventfd to receive notifications from the guest on
the specified Hyper-V connection id through the SIGNAL_EVENT hypercall, without
causing a user exit.  SIGNAL_EVENT hypercall with non-zero event flag number
(bits 24-31) still triggers a KVM_EXIT_HYPERV_HCALL user exit.

struct kvm_hyperv_eventfd {
	__u32 conn_id;
	__s32 fd;
	__u32 flags;
	__u32 padding[3];
};

The conn_id field should fit within 24 bits:

#define KVM_HYPERV_CONN_ID_MASK		0x00ffffff

The acceptable values for the flags field are:

#define KVM_HYPERV_EVENTFD_DEASSIGN	(1 << 0)

Returns: 0 on success,
	-EINVAL if conn_id or flags is outside the allowed range
	-ENOENT on deassign if the conn_id isn't registered
	-EEXIST on assign if the conn_id is already registered

4.114 KVM_GET_NESTED_STATE

Capability: KVM_CAP_NESTED_STATE
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_nested_state (in/out)
Returns: 0 on success, -1 on error
Errors:
  E2BIG:     the total state size exceeds the value of 'size' specified by
             the user; the size required will be written into size.

struct kvm_nested_state {
	__u16 flags;
	__u16 format;
	__u32 size;

	union {
		struct kvm_vmx_nested_state_hdr vmx;
		struct kvm_svm_nested_state_hdr svm;

		/* Pad the header to 128 bytes.  */
		__u8 pad[120];
	} hdr;

	union {
		struct kvm_vmx_nested_state_data vmx[0];
		struct kvm_svm_nested_state_data svm[0];
	} data;
};

#define KVM_STATE_NESTED_GUEST_MODE	0x00000001
#define KVM_STATE_NESTED_RUN_PENDING	0x00000002
#define KVM_STATE_NESTED_EVMCS		0x00000004

#define KVM_STATE_NESTED_FORMAT_VMX		0
#define KVM_STATE_NESTED_FORMAT_SVM		1

#define KVM_STATE_NESTED_VMX_VMCS_SIZE		0x1000

#define KVM_STATE_NESTED_VMX_SMM_GUEST_MODE	0x00000001
#define KVM_STATE_NESTED_VMX_SMM_VMXON		0x00000002

struct kvm_vmx_nested_state_hdr {
	__u64 vmxon_pa;
	__u64 vmcs12_pa;

	struct {
		__u16 flags;
	} smm;
};

struct kvm_vmx_nested_state_data {
	__u8 vmcs12[KVM_STATE_NESTED_VMX_VMCS_SIZE];
	__u8 shadow_vmcs12[KVM_STATE_NESTED_VMX_VMCS_SIZE];
};

This ioctl copies the vcpu's nested virtualization state from the kernel to
userspace.

The maximum size of the state can be retrieved by passing KVM_CAP_NESTED_STATE
to the KVM_CHECK_EXTENSION ioctl().

4.115 KVM_SET_NESTED_STATE

Capability: KVM_CAP_NESTED_STATE
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_nested_state (in)
Returns: 0 on success, -1 on error

This copies the vcpu's kvm_nested_state struct from userspace to the kernel.
For the definition of struct kvm_nested_state, see KVM_GET_NESTED_STATE.

4.116 KVM_(UN)REGISTER_COALESCED_MMIO

Capability: KVM_CAP_COALESCED_MMIO (for coalesced mmio)
	    KVM_CAP_COALESCED_PIO (for coalesced pio)
Architectures: all
Type: vm ioctl
Parameters: struct kvm_coalesced_mmio_zone
Returns: 0 on success, < 0 on error

Coalesced I/O is a performance optimization that defers hardware
register write emulation so that userspace exits are avoided.  It is
typically used to reduce the overhead of emulating frequently accessed
hardware registers.

When a hardware register is configured for coalesced I/O, write accesses
do not exit to userspace and their value is recorded in a ring buffer
that is shared between kernel and userspace.

Coalesced I/O is used if one or more write accesses to a hardware
register can be deferred until a read or a write to another hardware
register on the same device.  This last access will cause a vmexit and
userspace will process accesses from the ring buffer before emulating
it. That will avoid exiting to userspace on repeated writes.

Coalesced pio is based on coalesced mmio. There is little difference
between coalesced mmio and pio except that coalesced pio records accesses
to I/O ports.

4.117 KVM_CLEAR_DIRTY_LOG (vm ioctl)

Capability: KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2
Architectures: x86, arm, arm64, mips
Type: vm ioctl
Parameters: struct kvm_dirty_log (in)
Returns: 0 on success, -1 on error

/* for KVM_CLEAR_DIRTY_LOG */
struct kvm_clear_dirty_log {
	__u32 slot;
	__u32 num_pages;
	__u64 first_page;
	union {
		void __user *dirty_bitmap; /* one bit per page */
		__u64 padding;
	};
};

The ioctl clears the dirty status of pages in a memory slot, according to
the bitmap that is passed in struct kvm_clear_dirty_log's dirty_bitmap
field.  Bit 0 of the bitmap corresponds to page "first_page" in the
memory slot, and num_pages is the size in bits of the input bitmap.
first_page must be a multiple of 64; num_pages must also be a multiple of
64 unless first_page + num_pages is the size of the memory slot.  For each
bit that is set in the input bitmap, the corresponding page is marked "clean"
in KVM's dirty bitmap, and dirty tracking is re-enabled for that page
(for example via write-protection, or by clearing the dirty bit in
a page table entry).

If KVM_CAP_MULTI_ADDRESS_SPACE is available, bits 16-31 specifies
the address space for which you want to return the dirty bitmap.
They must be less than the value that KVM_CHECK_EXTENSION returns for
the KVM_CAP_MULTI_ADDRESS_SPACE capability.

This ioctl is mostly useful when KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2
is enabled; for more information, see the description of the capability.
However, it can always be used as long as KVM_CHECK_EXTENSION confirms
that KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 is present.

4.118 KVM_GET_SUPPORTED_HV_CPUID

Capability: KVM_CAP_HYPERV_CPUID
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_cpuid2 (in/out)
Returns: 0 on success, -1 on error

struct kvm_cpuid2 {
	__u32 nent;
	__u32 padding;
	struct kvm_cpuid_entry2 entries[0];
};

struct kvm_cpuid_entry2 {
	__u32 function;
	__u32 index;
	__u32 flags;
	__u32 eax;
	__u32 ebx;
	__u32 ecx;
	__u32 edx;
	__u32 padding[3];
};

This ioctl returns x86 cpuid features leaves related to Hyper-V emulation in
KVM.  Userspace can use the information returned by this ioctl to construct
cpuid information presented to guests consuming Hyper-V enlightenments (e.g.
Windows or Hyper-V guests).

CPUID feature leaves returned by this ioctl are defined by Hyper-V Top Level
Functional Specification (TLFS). These leaves can't be obtained with
KVM_GET_SUPPORTED_CPUID ioctl because some of them intersect with KVM feature
leaves (0x40000000, 0x40000001).

Currently, the following list of CPUID leaves are returned:
 HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS
 HYPERV_CPUID_INTERFACE
 HYPERV_CPUID_VERSION
 HYPERV_CPUID_FEATURES
 HYPERV_CPUID_ENLIGHTMENT_INFO
 HYPERV_CPUID_IMPLEMENT_LIMITS
 HYPERV_CPUID_NESTED_FEATURES

HYPERV_CPUID_NESTED_FEATURES leaf is only exposed when Enlightened VMCS was
enabled on the corresponding vCPU (KVM_CAP_HYPERV_ENLIGHTENED_VMCS).

Userspace invokes KVM_GET_SUPPORTED_CPUID by passing a kvm_cpuid2 structure
with the 'nent' field indicating the number of entries in the variable-size
array 'entries'.  If the number of entries is too low to describe all Hyper-V
feature leaves, an error (E2BIG) is returned. If the number is more or equal
to the number of Hyper-V feature leaves, the 'nent' field is adjusted to the
number of valid entries in the 'entries' array, which is then filled.

'index' and 'flags' fields in 'struct kvm_cpuid_entry2' are currently reserved,
userspace should not expect to get any particular value there.

4.119 KVM_ARM_VCPU_FINALIZE

Architectures: arm, arm64
Type: vcpu ioctl
Parameters: int feature (in)
Returns: 0 on success, -1 on error
Errors:
  EPERM:     feature not enabled, needs configuration, or already finalized
  EINVAL:    feature unknown or not present

Recognised values for feature:
  arm64      KVM_ARM_VCPU_SVE (requires KVM_CAP_ARM_SVE)

Finalizes the configuration of the specified vcpu feature.

The vcpu must already have been initialised, enabling the affected feature, by
means of a successful KVM_ARM_VCPU_INIT call with the appropriate flag set in
features[].

For affected vcpu features, this is a mandatory step that must be performed
before the vcpu is fully usable.

Between KVM_ARM_VCPU_INIT and KVM_ARM_VCPU_FINALIZE, the feature may be
configured by use of ioctls such as KVM_SET_ONE_REG.  The exact configuration
that should be performaned and how to do it are feature-dependent.

Other calls that depend on a particular feature being finalized, such as
KVM_RUN, KVM_GET_REG_LIST, KVM_GET_ONE_REG and KVM_SET_ONE_REG, will fail with
-EPERM unless the feature has already been finalized by means of a
KVM_ARM_VCPU_FINALIZE call.

See KVM_ARM_VCPU_INIT for details of vcpu features that require finalization
using this ioctl.

4.120 KVM_SET_PMU_EVENT_FILTER

Capability: KVM_CAP_PMU_EVENT_FILTER
Architectures: x86
Type: vm ioctl
Parameters: struct kvm_pmu_event_filter (in)
Returns: 0 on success, -1 on error

struct kvm_pmu_event_filter {
	__u32 action;
	__u32 nevents;
	__u32 fixed_counter_bitmap;
	__u32 flags;
	__u32 pad[4];
	__u64 events[0];
};

This ioctl restricts the set of PMU events that the guest can program.
The argument holds a list of events which will be allowed or denied.
The eventsel+umask of each event the guest attempts to program is compared
against the events field to determine whether the guest should have access.
The events field only controls general purpose counters; fixed purpose
counters are controlled by the fixed_counter_bitmap.

No flags are defined yet, the field must be zero.

Valid values for 'action':
#define KVM_PMU_EVENT_ALLOW 0
#define KVM_PMU_EVENT_DENY 1


5. The kvm_run structure
------------------------

Application code obtains a pointer to the kvm_run structure by
mmap()ing a vcpu fd.  From that point, application code can control
execution by changing fields in kvm_run prior to calling the KVM_RUN
ioctl, and obtain information about the reason KVM_RUN returned by
looking up structure members.

struct kvm_run {
	/* in */
	__u8 request_interrupt_window;

Request that KVM_RUN return when it becomes possible to inject external
interrupts into the guest.  Useful in conjunction with KVM_INTERRUPT.

	__u8 immediate_exit;

This field is polled once when KVM_RUN starts; if non-zero, KVM_RUN
exits immediately, returning -EINTR.  In the common scenario where a
signal is used to "kick" a VCPU out of KVM_RUN, this field can be used
to avoid usage of KVM_SET_SIGNAL_MASK, which has worse scalability.
Rather than blocking the signal outside KVM_RUN, userspace can set up
a signal handler that sets run->immediate_exit to a non-zero value.

This field is ignored if KVM_CAP_IMMEDIATE_EXIT is not available.

	__u8 padding1[6];

	/* out */
	__u32 exit_reason;

When KVM_RUN has returned successfully (return value 0), this informs
application code why KVM_RUN has returned.  Allowable values for this
field are detailed below.

	__u8 ready_for_interrupt_injection;

If request_interrupt_window has been specified, this field indicates
an interrupt can be injected now with KVM_INTERRUPT.

	__u8 if_flag;

The value of the current interrupt flag.  Only valid if in-kernel
local APIC is not used.

	__u16 flags;

More architecture-specific flags detailing state of the VCPU that may
affect the device's behavior.  The only currently defined flag is
KVM_RUN_X86_SMM, which is valid on x86 machines and is set if the
VCPU is in system management mode.

	/* in (pre_kvm_run), out (post_kvm_run) */
	__u64 cr8;

The value of the cr8 register.  Only valid if in-kernel local APIC is
not used.  Both input and output.

	__u64 apic_base;

The value of the APIC BASE msr.  Only valid if in-kernel local
APIC is not used.  Both input and output.

	union {
		/* KVM_EXIT_UNKNOWN */
		struct {
			__u64 hardware_exit_reason;
		} hw;

If exit_reason is KVM_EXIT_UNKNOWN, the vcpu has exited due to unknown
reasons.  Further architecture-specific information is available in
hardware_exit_reason.

		/* KVM_EXIT_FAIL_ENTRY */
		struct {
			__u64 hardware_entry_failure_reason;
		} fail_entry;

If exit_reason is KVM_EXIT_FAIL_ENTRY, the vcpu could not be run due
to unknown reasons.  Further architecture-specific information is
available in hardware_entry_failure_reason.

		/* KVM_EXIT_EXCEPTION */
		struct {
			__u32 exception;
			__u32 error_code;
		} ex;

Unused.

		/* KVM_EXIT_IO */
		struct {
#define KVM_EXIT_IO_IN  0
#define KVM_EXIT_IO_OUT 1
			__u8 direction;
			__u8 size; /* bytes */
			__u16 port;
			__u32 count;
			__u64 data_offset; /* relative to kvm_run start */
		} io;

If exit_reason is KVM_EXIT_IO, then the vcpu has
executed a port I/O instruction which could not be satisfied by kvm.
data_offset describes where the data is located (KVM_EXIT_IO_OUT) or
where kvm expects application code to place the data for the next
KVM_RUN invocation (KVM_EXIT_IO_IN).  Data format is a packed array.

		/* KVM_EXIT_DEBUG */
		struct {
			struct kvm_debug_exit_arch arch;
		} debug;

If the exit_reason is KVM_EXIT_DEBUG, then a vcpu is processing a debug event
for which architecture specific information is returned.

		/* KVM_EXIT_MMIO */
		struct {
			__u64 phys_addr;
			__u8  data[8];
			__u32 len;
			__u8  is_write;
		} mmio;

If exit_reason is KVM_EXIT_MMIO, then the vcpu has
executed a memory-mapped I/O instruction which could not be satisfied
by kvm.  The 'data' member contains the written data if 'is_write' is
true, and should be filled by application code otherwise.

The 'data' member contains, in its first 'len' bytes, the value as it would
appear if the VCPU performed a load or store of the appropriate width directly
to the byte array.

NOTE: For KVM_EXIT_IO, KVM_EXIT_MMIO, KVM_EXIT_OSI, KVM_EXIT_PAPR and
      KVM_EXIT_EPR the corresponding
operations are complete (and guest state is consistent) only after userspace
has re-entered the kernel with KVM_RUN.  The kernel side will first finish
incomplete operations and then check for pending signals.  Userspace
can re-enter the guest with an unmasked signal pending to complete
pending operations.

		/* KVM_EXIT_HYPERCALL */
		struct {
			__u64 nr;
			__u64 args[6];
			__u64 ret;
			__u32 longmode;
			__u32 pad;
		} hypercall;

Unused.  This was once used for 'hypercall to userspace'.  To implement
such functionality, use KVM_EXIT_IO (x86) or KVM_EXIT_MMIO (all except s390).
Note KVM_EXIT_IO is significantly faster than KVM_EXIT_MMIO.

		/* KVM_EXIT_TPR_ACCESS */
		struct {
			__u64 rip;
			__u32 is_write;
			__u32 pad;
		} tpr_access;

To be documented (KVM_TPR_ACCESS_REPORTING).

		/* KVM_EXIT_S390_SIEIC */
		struct {
			__u8 icptcode;
			__u64 mask; /* psw upper half */
			__u64 addr; /* psw lower half */
			__u16 ipa;
			__u32 ipb;
		} s390_sieic;

s390 specific.

		/* KVM_EXIT_S390_RESET */
#define KVM_S390_RESET_POR       1
#define KVM_S390_RESET_CLEAR     2
#define KVM_S390_RESET_SUBSYSTEM 4
#define KVM_S390_RESET_CPU_INIT  8
#define KVM_S390_RESET_IPL       16
		__u64 s390_reset_flags;

s390 specific.

		/* KVM_EXIT_S390_UCONTROL */
		struct {
			__u64 trans_exc_code;
			__u32 pgm_code;
		} s390_ucontrol;

s390 specific. A page fault has occurred for a user controlled virtual
machine (KVM_VM_S390_UNCONTROL) on it's host page table that cannot be
resolved by the kernel.
The program code and the translation exception code that were placed
in the cpu's lowcore are presented here as defined by the z Architecture
Principles of Operation Book in the Chapter for Dynamic Address Translation
(DAT)

		/* KVM_EXIT_DCR */
		struct {
			__u32 dcrn;
			__u32 data;
			__u8  is_write;
		} dcr;

Deprecated - was used for 440 KVM.

		/* KVM_EXIT_OSI */
		struct {
			__u64 gprs[32];
		} osi;

MOL uses a special hypercall interface it calls 'OSI'. To enable it, we catch
hypercalls and exit with this exit struct that contains all the guest gprs.

If exit_reason is KVM_EXIT_OSI, then the vcpu has triggered such a hypercall.
Userspace can now handle the hypercall and when it's done modify the gprs as
necessary. Upon guest entry all guest GPRs will then be replaced by the values
in this struct.

		/* KVM_EXIT_PAPR_HCALL */
		struct {
			__u64 nr;
			__u64 ret;
			__u64 args[9];
		} papr_hcall;

This is used on 64-bit PowerPC when emulating a pSeries partition,
e.g. with the 'pseries' machine type in qemu.  It occurs when the
guest does a hypercall using the 'sc 1' instruction.  The 'nr' field
contains the hypercall number (from the guest R3), and 'args' contains
the arguments (from the guest R4 - R12).  Userspace should put the
return code in 'ret' and any extra returned values in args[].
The possible hypercalls are defined in the Power Architecture Platform
Requirements (PAPR) document available from www.power.org (free
developer registration required to access it).

		/* KVM_EXIT_S390_TSCH */
		struct {
			__u16 subchannel_id;
			__u16 subchannel_nr;
			__u32 io_int_parm;
			__u32 io_int_word;
			__u32 ipb;
			__u8 dequeued;
		} s390_tsch;

s390 specific. This exit occurs when KVM_CAP_S390_CSS_SUPPORT has been enabled
and TEST SUBCHANNEL was intercepted. If dequeued is set, a pending I/O
interrupt for the target subchannel has been dequeued and subchannel_id,
subchannel_nr, io_int_parm and io_int_word contain the parameters for that
interrupt. ipb is needed for instruction parameter decoding.

		/* KVM_EXIT_EPR */
		struct {
			__u32 epr;
		} epr;

On FSL BookE PowerPC chips, the interrupt controller has a fast patch
interrupt acknowledge path to the core. When the core successfully
delivers an interrupt, it automatically populates the EPR register with
the interrupt vector number and acknowledges the interrupt inside
the interrupt controller.

In case the interrupt controller lives in user space, we need to do
the interrupt acknowledge cycle through it to fetch the next to be
delivered interrupt vector using this exit.

It gets triggered whenever both KVM_CAP_PPC_EPR are enabled and an
external interrupt has just been delivered into the guest. User space
should put the acknowledged interrupt vector into the 'epr' field.

		/* KVM_EXIT_SYSTEM_EVENT */
		struct {
#define KVM_SYSTEM_EVENT_SHUTDOWN       1
#define KVM_SYSTEM_EVENT_RESET          2
#define KVM_SYSTEM_EVENT_CRASH          3
			__u32 type;
			__u64 flags;
		} system_event;

If exit_reason is KVM_EXIT_SYSTEM_EVENT then the vcpu has triggered
a system-level event using some architecture specific mechanism (hypercall
or some special instruction). In case of ARM/ARM64, this is triggered using
HVC instruction based PSCI call from the vcpu. The 'type' field describes
the system-level event type. The 'flags' field describes architecture
specific flags for the system-level event.

Valid values for 'type' are:
  KVM_SYSTEM_EVENT_SHUTDOWN -- the guest has requested a shutdown of the
   VM. Userspace is not obliged to honour this, and if it does honour
   this does not need to destroy the VM synchronously (ie it may call
   KVM_RUN again before shutdown finally occurs).
  KVM_SYSTEM_EVENT_RESET -- the guest has requested a reset of the VM.
   As with SHUTDOWN, userspace can choose to ignore the request, or
   to schedule the reset to occur in the future and may call KVM_RUN again.
  KVM_SYSTEM_EVENT_CRASH -- the guest crash occurred and the guest
   has requested a crash condition maintenance. Userspace can choose
   to ignore the request, or to gather VM memory core dump and/or
   reset/shutdown of the VM.

		/* KVM_EXIT_IOAPIC_EOI */
		struct {
			__u8 vector;
		} eoi;

Indicates that the VCPU's in-kernel local APIC received an EOI for a
level-triggered IOAPIC interrupt.  This exit only triggers when the
IOAPIC is implemented in userspace (i.e. KVM_CAP_SPLIT_IRQCHIP is enabled);
the userspace IOAPIC should process the EOI and retrigger the interrupt if
it is still asserted.  Vector is the LAPIC interrupt vector for which the
EOI was received.

		struct kvm_hyperv_exit {
#define KVM_EXIT_HYPERV_SYNIC          1
#define KVM_EXIT_HYPERV_HCALL          2
			__u32 type;
			union {
				struct {
					__u32 msr;
					__u64 control;
					__u64 evt_page;
					__u64 msg_page;
				} synic;
				struct {
					__u64 input;
					__u64 result;
					__u64 params[2];
				} hcall;
			} u;
		};
		/* KVM_EXIT_HYPERV */
                struct kvm_hyperv_exit hyperv;
Indicates that the VCPU exits into userspace to process some tasks
related to Hyper-V emulation.
Valid values for 'type' are:
	KVM_EXIT_HYPERV_SYNIC -- synchronously notify user-space about
Hyper-V SynIC state change. Notification is used to remap SynIC
event/message pages and to enable/disable SynIC messages/events processing
in userspace.

		/* Fix the size of the union. */
		char padding[256];
	};

	/*
	 * shared registers between kvm and userspace.
	 * kvm_valid_regs specifies the register classes set by the host
	 * kvm_dirty_regs specified the register classes dirtied by userspace
	 * struct kvm_sync_regs is architecture specific, as well as the
	 * bits for kvm_valid_regs and kvm_dirty_regs
	 */
	__u64 kvm_valid_regs;
	__u64 kvm_dirty_regs;
	union {
		struct kvm_sync_regs regs;
		char padding[SYNC_REGS_SIZE_BYTES];
	} s;

If KVM_CAP_SYNC_REGS is defined, these fields allow userspace to access
certain guest registers without having to call SET/GET_*REGS. Thus we can
avoid some system call overhead if userspace has to handle the exit.
Userspace can query the validity of the structure by checking
kvm_valid_regs for specific bits. These bits are architecture specific
and usually define the validity of a groups of registers. (e.g. one bit
 for general purpose registers)

Please note that the kernel is allowed to use the kvm_run structure as the
primary storage for certain register types. Therefore, the kernel may use the
values in kvm_run even if the corresponding bit in kvm_dirty_regs is not set.

};



6. Capabilities that can be enabled on vCPUs
--------------------------------------------

There are certain capabilities that change the behavior of the virtual CPU or
the virtual machine when enabled. To enable them, please see section 4.37.
Below you can find a list of capabilities and what their effect on the vCPU or
the virtual machine is when enabling them.

The following information is provided along with the description:

  Architectures: which instruction set architectures provide this ioctl.
      x86 includes both i386 and x86_64.

  Target: whether this is a per-vcpu or per-vm capability.

  Parameters: what parameters are accepted by the capability.

  Returns: the return value.  General error numbers (EBADF, ENOMEM, EINVAL)
      are not detailed, but errors with specific meanings are.


6.1 KVM_CAP_PPC_OSI

Architectures: ppc
Target: vcpu
Parameters: none
Returns: 0 on success; -1 on error

This capability enables interception of OSI hypercalls that otherwise would
be treated as normal system calls to be injected into the guest. OSI hypercalls
were invented by Mac-on-Linux to have a standardized communication mechanism
between the guest and the host.

When this capability is enabled, KVM_EXIT_OSI can occur.


6.2 KVM_CAP_PPC_PAPR

Architectures: ppc
Target: vcpu
Parameters: none
Returns: 0 on success; -1 on error

This capability enables interception of PAPR hypercalls. PAPR hypercalls are
done using the hypercall instruction "sc 1".

It also sets the guest privilege level to "supervisor" mode. Usually the guest
runs in "hypervisor" privilege mode with a few missing features.

In addition to the above, it changes the semantics of SDR1. In this mode, the
HTAB address part of SDR1 contains an HVA instead of a GPA, as PAPR keeps the
HTAB invisible to the guest.

When this capability is enabled, KVM_EXIT_PAPR_HCALL can occur.


6.3 KVM_CAP_SW_TLB

Architectures: ppc
Target: vcpu
Parameters: args[0] is the address of a struct kvm_config_tlb
Returns: 0 on success; -1 on error

struct kvm_config_tlb {
	__u64 params;
	__u64 array;
	__u32 mmu_type;
	__u32 array_len;
};

Configures the virtual CPU's TLB array, establishing a shared memory area
between userspace and KVM.  The "params" and "array" fields are userspace
addresses of mmu-type-specific data structures.  The "array_len" field is an
safety mechanism, and should be set to the size in bytes of the memory that
userspace has reserved for the array.  It must be at least the size dictated
by "mmu_type" and "params".

While KVM_RUN is active, the shared region is under control of KVM.  Its
contents are undefined, and any modification by userspace results in
boundedly undefined behavior.

On return from KVM_RUN, the shared region will reflect the current state of
the guest's TLB.  If userspace makes any changes, it must call KVM_DIRTY_TLB
to tell KVM which entries have been changed, prior to calling KVM_RUN again
on this vcpu.

For mmu types KVM_MMU_FSL_BOOKE_NOHV and KVM_MMU_FSL_BOOKE_HV:
 - The "params" field is of type "struct kvm_book3e_206_tlb_params".
 - The "array" field points to an array of type "struct
   kvm_book3e_206_tlb_entry".
 - The array consists of all entries in the first TLB, followed by all
   entries in the second TLB.
 - Within a TLB, entries are ordered first by increasing set number.  Within a
   set, entries are ordered by way (increasing ESEL).
 - The hash for determining set number in TLB0 is: (MAS2 >> 12) & (num_sets - 1)
   where "num_sets" is the tlb_sizes[] value divided by the tlb_ways[] value.
 - The tsize field of mas1 shall be set to 4K on TLB0, even though the
   hardware ignores this value for TLB0.

6.4 KVM_CAP_S390_CSS_SUPPORT

Architectures: s390
Target: vcpu
Parameters: none
Returns: 0 on success; -1 on error

This capability enables support for handling of channel I/O instructions.

TEST PENDING INTERRUPTION and the interrupt portion of TEST SUBCHANNEL are
handled in-kernel, while the other I/O instructions are passed to userspace.

When this capability is enabled, KVM_EXIT_S390_TSCH will occur on TEST
SUBCHANNEL intercepts.

Note that even though this capability is enabled per-vcpu, the complete
virtual machine is affected.

6.5 KVM_CAP_PPC_EPR

Architectures: ppc
Target: vcpu
Parameters: args[0] defines whether the proxy facility is active
Returns: 0 on success; -1 on error

This capability enables or disables the delivery of interrupts through the
external proxy facility.

When enabled (args[0] != 0), every time the guest gets an external interrupt
delivered, it automatically exits into user space with a KVM_EXIT_EPR exit
to receive the topmost interrupt vector.

When disabled (args[0] == 0), behavior is as if this facility is unsupported.

When this capability is enabled, KVM_EXIT_EPR can occur.

6.6 KVM_CAP_IRQ_MPIC

Architectures: ppc
Parameters: args[0] is the MPIC device fd
            args[1] is the MPIC CPU number for this vcpu

This capability connects the vcpu to an in-kernel MPIC device.

6.7 KVM_CAP_IRQ_XICS

Architectures: ppc
Target: vcpu
Parameters: args[0] is the XICS device fd
            args[1] is the XICS CPU number (server ID) for this vcpu

This capability connects the vcpu to an in-kernel XICS device.

6.8 KVM_CAP_S390_IRQCHIP

Architectures: s390
Target: vm
Parameters: none

This capability enables the in-kernel irqchip for s390. Please refer to
"4.24 KVM_CREATE_IRQCHIP" for details.

6.9 KVM_CAP_MIPS_FPU

Architectures: mips
Target: vcpu
Parameters: args[0] is reserved for future use (should be 0).

This capability allows the use of the host Floating Point Unit by the guest. It
allows the Config1.FP bit to be set to enable the FPU in the guest. Once this is
done the KVM_REG_MIPS_FPR_* and KVM_REG_MIPS_FCR_* registers can be accessed
(depending on the current guest FPU register mode), and the Status.FR,
Config5.FRE bits are accessible via the KVM API and also from the guest,
depending on them being supported by the FPU.

6.10 KVM_CAP_MIPS_MSA

Architectures: mips
Target: vcpu
Parameters: args[0] is reserved for future use (should be 0).

This capability allows the use of the MIPS SIMD Architecture (MSA) by the guest.
It allows the Config3.MSAP bit to be set to enable the use of MSA by the guest.
Once this is done the KVM_REG_MIPS_VEC_* and KVM_REG_MIPS_MSA_* registers can be
accessed, and the Config5.MSAEn bit is accessible via the KVM API and also from
the guest.

6.74 KVM_CAP_SYNC_REGS
Architectures: s390, x86
Target: s390: always enabled, x86: vcpu
Parameters: none
Returns: x86: KVM_CHECK_EXTENSION returns a bit-array indicating which register
sets are supported (bitfields defined in arch/x86/include/uapi/asm/kvm.h).

As described above in the kvm_sync_regs struct info in section 5 (kvm_run):
KVM_CAP_SYNC_REGS "allow[s] userspace to access certain guest registers
without having to call SET/GET_*REGS". This reduces overhead by eliminating
repeated ioctl calls for setting and/or getting register values. This is
particularly important when userspace is making synchronous guest state
modifications, e.g. when emulating and/or intercepting instructions in
userspace.

For s390 specifics, please refer to the source code.

For x86:
- the register sets to be copied out to kvm_run are selectable
  by userspace (rather that all sets being copied out for every exit).
- vcpu_events are available in addition to regs and sregs.

For x86, the 'kvm_valid_regs' field of struct kvm_run is overloaded to
function as an input bit-array field set by userspace to indicate the
specific register sets to be copied out on the next exit.

To indicate when userspace has modified values that should be copied into
the vCPU, the all architecture bitarray field, 'kvm_dirty_regs' must be set.
This is done using the same bitflags as for the 'kvm_valid_regs' field.
If the dirty bit is not set, then the register set values will not be copied
into the vCPU even if they've been modified.

Unused bitfields in the bitarrays must be set to zero.

struct kvm_sync_regs {
        struct kvm_regs regs;
        struct kvm_sregs sregs;
        struct kvm_vcpu_events events;
};

6.75 KVM_CAP_PPC_IRQ_XIVE

Architectures: ppc
Target: vcpu
Parameters: args[0] is the XIVE device fd
            args[1] is the XIVE CPU number (server ID) for this vcpu

This capability connects the vcpu to an in-kernel XIVE device.

7. Capabilities that can be enabled on VMs
------------------------------------------

There are certain capabilities that change the behavior of the virtual
machine when enabled. To enable them, please see section 4.37. Below
you can find a list of capabilities and what their effect on the VM
is when enabling them.

The following information is provided along with the description:

  Architectures: which instruction set architectures provide this ioctl.
      x86 includes both i386 and x86_64.

  Parameters: what parameters are accepted by the capability.

  Returns: the return value.  General error numbers (EBADF, ENOMEM, EINVAL)
      are not detailed, but errors with specific meanings are.


7.1 KVM_CAP_PPC_ENABLE_HCALL

Architectures: ppc
Parameters: args[0] is the sPAPR hcall number
	    args[1] is 0 to disable, 1 to enable in-kernel handling

This capability controls whether individual sPAPR hypercalls (hcalls)
get handled by the kernel or not.  Enabling or disabling in-kernel
handling of an hcall is effective across the VM.  On creation, an
initial set of hcalls are enabled for in-kernel handling, which
consists of those hcalls for which in-kernel handlers were implemented
before this capability was implemented.  If disabled, the kernel will
not to attempt to handle the hcall, but will always exit to userspace
to handle it.  Note that it may not make sense to enable some and
disable others of a group of related hcalls, but KVM does not prevent
userspace from doing that.

If the hcall number specified is not one that has an in-kernel
implementation, the KVM_ENABLE_CAP ioctl will fail with an EINVAL
error.

7.2 KVM_CAP_S390_USER_SIGP

Architectures: s390
Parameters: none

This capability controls which SIGP orders will be handled completely in user
space. With this capability enabled, all fast orders will be handled completely
in the kernel:
- SENSE
- SENSE RUNNING
- EXTERNAL CALL
- EMERGENCY SIGNAL
- CONDITIONAL EMERGENCY SIGNAL

All other orders will be handled completely in user space.

Only privileged operation exceptions will be checked for in the kernel (or even
in the hardware prior to interception). If this capability is not enabled, the
old way of handling SIGP orders is used (partially in kernel and user space).

7.3 KVM_CAP_S390_VECTOR_REGISTERS

Architectures: s390
Parameters: none
Returns: 0 on success, negative value on error

Allows use of the vector registers introduced with z13 processor, and
provides for the synchronization between host and user space.  Will
return -EINVAL if the machine does not support vectors.

7.4 KVM_CAP_S390_USER_STSI

Architectures: s390
Parameters: none

This capability allows post-handlers for the STSI instruction. After
initial handling in the kernel, KVM exits to user space with
KVM_EXIT_S390_STSI to allow user space to insert further data.

Before exiting to userspace, kvm handlers should fill in s390_stsi field of
vcpu->run:
struct {
	__u64 addr;
	__u8 ar;
	__u8 reserved;
	__u8 fc;
	__u8 sel1;
	__u16 sel2;
} s390_stsi;

@addr - guest address of STSI SYSIB
@fc   - function code
@sel1 - selector 1
@sel2 - selector 2
@ar   - access register number

KVM handlers should exit to userspace with rc = -EREMOTE.

7.5 KVM_CAP_SPLIT_IRQCHIP

Architectures: x86
Parameters: args[0] - number of routes reserved for userspace IOAPICs
Returns: 0 on success, -1 on error

Create a local apic for each processor in the kernel. This can be used
instead of KVM_CREATE_IRQCHIP if the userspace VMM wishes to emulate the
IOAPIC and PIC (and also the PIT, even though this has to be enabled
separately).

This capability also enables in kernel routing of interrupt requests;
when KVM_CAP_SPLIT_IRQCHIP only routes of KVM_IRQ_ROUTING_MSI type are
used in the IRQ routing table.  The first args[0] MSI routes are reserved
for the IOAPIC pins.  Whenever the LAPIC receives an EOI for these routes,
a KVM_EXIT_IOAPIC_EOI vmexit will be reported to userspace.

Fails if VCPU has already been created, or if the irqchip is already in the
kernel (i.e. KVM_CREATE_IRQCHIP has already been called).

7.6 KVM_CAP_S390_RI

Architectures: s390
Parameters: none

Allows use of runtime-instrumentation introduced with zEC12 processor.
Will return -EINVAL if the machine does not support runtime-instrumentation.
Will return -EBUSY if a VCPU has already been created.

7.7 KVM_CAP_X2APIC_API

Architectures: x86
Parameters: args[0] - features that should be enabled
Returns: 0 on success, -EINVAL when args[0] contains invalid features

Valid feature flags in args[0] are

#define KVM_X2APIC_API_USE_32BIT_IDS            (1ULL << 0)
#define KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK  (1ULL << 1)

Enabling KVM_X2APIC_API_USE_32BIT_IDS changes the behavior of
KVM_SET_GSI_ROUTING, KVM_SIGNAL_MSI, KVM_SET_LAPIC, and KVM_GET_LAPIC,
allowing the use of 32-bit APIC IDs.  See KVM_CAP_X2APIC_API in their
respective sections.

KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK must be enabled for x2APIC to work
in logical mode or with more than 255 VCPUs.  Otherwise, KVM treats 0xff
as a broadcast even in x2APIC mode in order to support physical x2APIC
without interrupt remapping.  This is undesirable in logical mode,
where 0xff represents CPUs 0-7 in cluster 0.

7.8 KVM_CAP_S390_USER_INSTR0

Architectures: s390
Parameters: none

With this capability enabled, all illegal instructions 0x0000 (2 bytes) will
be intercepted and forwarded to user space. User space can use this
mechanism e.g. to realize 2-byte software breakpoints. The kernel will
not inject an operating exception for these instructions, user space has
to take care of that.

This capability can be enabled dynamically even if VCPUs were already
created and are running.

7.9 KVM_CAP_S390_GS

Architectures: s390
Parameters: none
Returns: 0 on success; -EINVAL if the machine does not support
	 guarded storage; -EBUSY if a VCPU has already been created.

Allows use of guarded storage for the KVM guest.

7.10 KVM_CAP_S390_AIS

Architectures: s390
Parameters: none

Allow use of adapter-interruption suppression.
Returns: 0 on success; -EBUSY if a VCPU has already been created.

7.11 KVM_CAP_PPC_SMT

Architectures: ppc
Parameters: vsmt_mode, flags

Enabling this capability on a VM provides userspace with a way to set
the desired virtual SMT mode (i.e. the number of virtual CPUs per
virtual core).  The virtual SMT mode, vsmt_mode, must be a power of 2
between 1 and 8.  On POWER8, vsmt_mode must also be no greater than
the number of threads per subcore for the host.  Currently flags must
be 0.  A successful call to enable this capability will result in
vsmt_mode being returned when the KVM_CAP_PPC_SMT capability is
subsequently queried for the VM.  This capability is only supported by
HV KVM, and can only be set before any VCPUs have been created.
The KVM_CAP_PPC_SMT_POSSIBLE capability indicates which virtual SMT
modes are available.

7.12 KVM_CAP_PPC_FWNMI

Architectures: ppc
Parameters: none

With this capability a machine check exception in the guest address
space will cause KVM to exit the guest with NMI exit reason. This
enables QEMU to build error log and branch to guest kernel registered
machine check handling routine. Without this capability KVM will
branch to guests' 0x200 interrupt vector.

7.13 KVM_CAP_X86_DISABLE_EXITS

Architectures: x86
Parameters: args[0] defines which exits are disabled
Returns: 0 on success, -EINVAL when args[0] contains invalid exits

Valid bits in args[0] are

#define KVM_X86_DISABLE_EXITS_MWAIT            (1 << 0)
#define KVM_X86_DISABLE_EXITS_HLT              (1 << 1)
#define KVM_X86_DISABLE_EXITS_PAUSE            (1 << 2)
#define KVM_X86_DISABLE_EXITS_CSTATE           (1 << 3)

Enabling this capability on a VM provides userspace with a way to no
longer intercept some instructions for improved latency in some
workloads, and is suggested when vCPUs are associated to dedicated
physical CPUs.  More bits can be added in the future; userspace can
just pass the KVM_CHECK_EXTENSION result to KVM_ENABLE_CAP to disable
all such vmexits.

Do not enable KVM_FEATURE_PV_UNHALT if you disable HLT exits.

7.14 KVM_CAP_S390_HPAGE_1M

Architectures: s390
Parameters: none
Returns: 0 on success, -EINVAL if hpage module parameter was not set
	 or cmma is enabled, or the VM has the KVM_VM_S390_UCONTROL
	 flag set

With this capability the KVM support for memory backing with 1m pages
through hugetlbfs can be enabled for a VM. After the capability is
enabled, cmma can't be enabled anymore and pfmfi and the storage key
interpretation are disabled. If cmma has already been enabled or the
hpage module parameter is not set to 1, -EINVAL is returned.

While it is generally possible to create a huge page backed VM without
this capability, the VM will not be able to run.

7.15 KVM_CAP_MSR_PLATFORM_INFO

Architectures: x86
Parameters: args[0] whether feature should be enabled or not

With this capability, a guest may read the MSR_PLATFORM_INFO MSR. Otherwise,
a #GP would be raised when the guest tries to access. Currently, this
capability does not enable write permissions of this MSR for the guest.

7.16 KVM_CAP_PPC_NESTED_HV

Architectures: ppc
Parameters: none
Returns: 0 on success, -EINVAL when the implementation doesn't support
	 nested-HV virtualization.

HV-KVM on POWER9 and later systems allows for "nested-HV"
virtualization, which provides a way for a guest VM to run guests that
can run using the CPU's supervisor mode (privileged non-hypervisor
state).  Enabling this capability on a VM depends on the CPU having
the necessary functionality and on the facility being enabled with a
kvm-hv module parameter.

7.17 KVM_CAP_EXCEPTION_PAYLOAD

Architectures: x86
Parameters: args[0] whether feature should be enabled or not

With this capability enabled, CR2 will not be modified prior to the
emulated VM-exit when L1 intercepts a #PF exception that occurs in
L2. Similarly, for kvm-intel only, DR6 will not be modified prior to
the emulated VM-exit when L1 intercepts a #DB exception that occurs in
L2. As a result, when KVM_GET_VCPU_EVENTS reports a pending #PF (or
#DB) exception for L2, exception.has_payload will be set and the
faulting address (or the new DR6 bits*) will be reported in the
exception_payload field. Similarly, when userspace injects a #PF (or
#DB) into L2 using KVM_SET_VCPU_EVENTS, it is expected to set
exception.has_payload and to put the faulting address (or the new DR6
bits*) in the exception_payload field.

This capability also enables exception.pending in struct
kvm_vcpu_events, which allows userspace to distinguish between pending
and injected exceptions.


* For the new DR6 bits, note that bit 16 is set iff the #DB exception
  will clear DR6.RTM.

7.18 KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2

Architectures: x86, arm, arm64, mips
Parameters: args[0] whether feature should be enabled or not

With this capability enabled, KVM_GET_DIRTY_LOG will not automatically
clear and write-protect all pages that are returned as dirty.
Rather, userspace will have to do this operation separately using
KVM_CLEAR_DIRTY_LOG.

At the cost of a slightly more complicated operation, this provides better
scalability and responsiveness for two reasons.  First,
KVM_CLEAR_DIRTY_LOG ioctl can operate on a 64-page granularity rather
than requiring to sync a full memslot; this ensures that KVM does not
take spinlocks for an extended period of time.  Second, in some cases a
large amount of time can pass between a call to KVM_GET_DIRTY_LOG and
userspace actually using the data in the page.  Pages can be modified
during this time, which is inefficint for both the guest and userspace:
the guest will incur a higher penalty due to write protection faults,
while userspace can see false reports of dirty pages.  Manual reprotection
helps reducing this time, improving guest performance and reducing the
number of dirty log false positives.

KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 was previously available under the name
KVM_CAP_MANUAL_DIRTY_LOG_PROTECT, but the implementation had bugs that make
it hard or impossible to use it correctly.  The availability of
KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 signals that those bugs are fixed.
Userspace should not try to use KVM_CAP_MANUAL_DIRTY_LOG_PROTECT.

8. Other capabilities.
----------------------

This section lists capabilities that give information about other
features of the KVM implementation.

8.1 KVM_CAP_PPC_HWRNG

Architectures: ppc

This capability, if KVM_CHECK_EXTENSION indicates that it is
available, means that that the kernel has an implementation of the
H_RANDOM hypercall backed by a hardware random-number generator.
If present, the kernel H_RANDOM handler can be enabled for guest use
with the KVM_CAP_PPC_ENABLE_HCALL capability.

8.2 KVM_CAP_HYPERV_SYNIC

Architectures: x86
This capability, if KVM_CHECK_EXTENSION indicates that it is
available, means that that the kernel has an implementation of the
Hyper-V Synthetic interrupt controller(SynIC). Hyper-V SynIC is
used to support Windows Hyper-V based guest paravirt drivers(VMBus).

In order to use SynIC, it has to be activated by setting this
capability via KVM_ENABLE_CAP ioctl on the vcpu fd. Note that this
will disable the use of APIC hardware virtualization even if supported
by the CPU, as it's incompatible with SynIC auto-EOI behavior.

8.3 KVM_CAP_PPC_RADIX_MMU

Architectures: ppc

This capability, if KVM_CHECK_EXTENSION indicates that it is
available, means that that the kernel can support guests using the
radix MMU defined in Power ISA V3.00 (as implemented in the POWER9
processor).

8.4 KVM_CAP_PPC_HASH_MMU_V3

Architectures: ppc

This capability, if KVM_CHECK_EXTENSION indicates that it is
available, means that that the kernel can support guests using the
hashed page table MMU defined in Power ISA V3.00 (as implemented in
the POWER9 processor), including in-memory segment tables.

8.5 KVM_CAP_MIPS_VZ

Architectures: mips

This capability, if KVM_CHECK_EXTENSION on the main kvm handle indicates that
it is available, means that full hardware assisted virtualization capabilities
of the hardware are available for use through KVM. An appropriate
KVM_VM_MIPS_* type must be passed to KVM_CREATE_VM to create a VM which
utilises it.

If KVM_CHECK_EXTENSION on a kvm VM handle indicates that this capability is
available, it means that the VM is using full hardware assisted virtualization
capabilities of the hardware. This is useful to check after creating a VM with
KVM_VM_MIPS_DEFAULT.

The value returned by KVM_CHECK_EXTENSION should be compared against known
values (see below). All other values are reserved. This is to allow for the
possibility of other hardware assisted virtualization implementations which
may be incompatible with the MIPS VZ ASE.

 0: The trap & emulate implementation is in use to run guest code in user
    mode. Guest virtual memory segments are rearranged to fit the guest in the
    user mode address space.

 1: The MIPS VZ ASE is in use, providing full hardware assisted
    virtualization, including standard guest virtual memory segments.

8.6 KVM_CAP_MIPS_TE

Architectures: mips

This capability, if KVM_CHECK_EXTENSION on the main kvm handle indicates that
it is available, means that the trap & emulate implementation is available to
run guest code in user mode, even if KVM_CAP_MIPS_VZ indicates that hardware
assisted virtualisation is also available. KVM_VM_MIPS_TE (0) must be passed
to KVM_CREATE_VM to create a VM which utilises it.

If KVM_CHECK_EXTENSION on a kvm VM handle indicates that this capability is
available, it means that the VM is using trap & emulate.

8.7 KVM_CAP_MIPS_64BIT

Architectures: mips

This capability indicates the supported architecture type of the guest, i.e. the
supported register and address width.

The values returned when this capability is checked by KVM_CHECK_EXTENSION on a
kvm VM handle correspond roughly to the CP0_Config.AT register field, and should
be checked specifically against known values (see below). All other values are
reserved.

 0: MIPS32 or microMIPS32.
    Both registers and addresses are 32-bits wide.
    It will only be possible to run 32-bit guest code.

 1: MIPS64 or microMIPS64 with access only to 32-bit compatibility segments.
    Registers are 64-bits wide, but addresses are 32-bits wide.
    64-bit guest code may run but cannot access MIPS64 memory segments.
    It will also be possible to run 32-bit guest code.

 2: MIPS64 or microMIPS64 with access to all address segments.
    Both registers and addresses are 64-bits wide.
    It will be possible to run 64-bit or 32-bit guest code.

8.9 KVM_CAP_ARM_USER_IRQ

Architectures: arm, arm64
This capability, if KVM_CHECK_EXTENSION indicates that it is available, means
that if userspace creates a VM without an in-kernel interrupt controller, it
will be notified of changes to the output level of in-kernel emulated devices,
which can generate virtual interrupts, presented to the VM.
For such VMs, on every return to userspace, the kernel
updates the vcpu's run->s.regs.device_irq_level field to represent the actual
output level of the device.

Whenever kvm detects a change in the device output level, kvm guarantees at
least one return to userspace before running the VM.  This exit could either
be a KVM_EXIT_INTR or any other exit event, like KVM_EXIT_MMIO. This way,
userspace can always sample the device output level and re-compute the state of
the userspace interrupt controller.  Userspace should always check the state
of run->s.regs.device_irq_level on every kvm exit.
The value in run->s.regs.device_irq_level can represent both level and edge
triggered interrupt signals, depending on the device.  Edge triggered interrupt
signals will exit to userspace with the bit in run->s.regs.device_irq_level
set exactly once per edge signal.

The field run->s.regs.device_irq_level is available independent of
run->kvm_valid_regs or run->kvm_dirty_regs bits.

If KVM_CAP_ARM_USER_IRQ is supported, the KVM_CHECK_EXTENSION ioctl returns a
number larger than 0 indicating the version of this capability is implemented
and thereby which bits in in run->s.regs.device_irq_level can signal values.

Currently the following bits are defined for the device_irq_level bitmap:

  KVM_CAP_ARM_USER_IRQ >= 1:

    KVM_ARM_DEV_EL1_VTIMER -  EL1 virtual timer
    KVM_ARM_DEV_EL1_PTIMER -  EL1 physical timer
    KVM_ARM_DEV_PMU        -  ARM PMU overflow interrupt signal

Future versions of kvm may implement additional events. These will get
indicated by returning a higher number from KVM_CHECK_EXTENSION and will be
listed above.

8.10 KVM_CAP_PPC_SMT_POSSIBLE

Architectures: ppc

Querying this capability returns a bitmap indicating the possible
virtual SMT modes that can be set using KVM_CAP_PPC_SMT.  If bit N
(counting from the right) is set, then a virtual SMT mode of 2^N is
available.

8.11 KVM_CAP_HYPERV_SYNIC2

Architectures: x86

This capability enables a newer version of Hyper-V Synthetic interrupt
controller (SynIC).  The only difference with KVM_CAP_HYPERV_SYNIC is that KVM
doesn't clear SynIC message and event flags pages when they are enabled by
writing to the respective MSRs.

8.12 KVM_CAP_HYPERV_VP_INDEX

Architectures: x86

This capability indicates that userspace can load HV_X64_MSR_VP_INDEX msr.  Its
value is used to denote the target vcpu for a SynIC interrupt.  For
compatibilty, KVM initializes this msr to KVM's internal vcpu index.  When this
capability is absent, userspace can still query this msr's value.

8.13 KVM_CAP_S390_AIS_MIGRATION

Architectures: s390
Parameters: none

This capability indicates if the flic device will be able to get/set the
AIS states for migration via the KVM_DEV_FLIC_AISM_ALL attribute and allows
to discover this without having to create a flic device.

8.14 KVM_CAP_S390_PSW

Architectures: s390

This capability indicates that the PSW is exposed via the kvm_run structure.

8.15 KVM_CAP_S390_GMAP

Architectures: s390

This capability indicates that the user space memory used as guest mapping can
be anywhere in the user memory address space, as long as the memory slots are
aligned and sized to a segment (1MB) boundary.

8.16 KVM_CAP_S390_COW

Architectures: s390

This capability indicates that the user space memory used as guest mapping can
use copy-on-write semantics as well as dirty pages tracking via read-only page
tables.

8.17 KVM_CAP_S390_BPB

Architectures: s390

This capability indicates that kvm will implement the interfaces to handle
reset, migration and nested KVM for branch prediction blocking. The stfle
facility 82 should not be provided to the guest without this capability.

8.18 KVM_CAP_HYPERV_TLBFLUSH

Architectures: x86

This capability indicates that KVM supports paravirtualized Hyper-V TLB Flush
hypercalls:
HvFlushVirtualAddressSpace, HvFlushVirtualAddressSpaceEx,
HvFlushVirtualAddressList, HvFlushVirtualAddressListEx.

8.19 KVM_CAP_ARM_INJECT_SERROR_ESR

Architectures: arm, arm64

This capability indicates that userspace can specify (via the
KVM_SET_VCPU_EVENTS ioctl) the syndrome value reported to the guest when it
takes a virtual SError interrupt exception.
If KVM advertises this capability, userspace can only specify the ISS field for
the ESR syndrome. Other parts of the ESR, such as the EC are generated by the
CPU when the exception is taken. If this virtual SError is taken to EL1 using
AArch64, this value will be reported in the ISS field of ESR_ELx.

See KVM_CAP_VCPU_EVENTS for more details.
8.20 KVM_CAP_HYPERV_SEND_IPI

Architectures: x86

This capability indicates that KVM supports paravirtualized Hyper-V IPI send
hypercalls:
HvCallSendSyntheticClusterIpi, HvCallSendSyntheticClusterIpiEx.
8.21 KVM_CAP_HYPERV_DIRECT_TLBFLUSH

Architecture: x86

This capability indicates that KVM running on top of Hyper-V hypervisor
enables Direct TLB flush for its guests meaning that TLB flush
hypercalls are handled by Level 0 hypervisor (Hyper-V) bypassing KVM.
Due to the different ABI for hypercall parameters between Hyper-V and
KVM, enabling this capability effectively disables all hypercall
handling by KVM (as some KVM hypercall may be mistakenly treated as TLB
flush hypercalls by Hyper-V) so userspace should disable KVM identification
in CPUID and only exposes Hyper-V identification. In this case, guest
thinks it's running on Hyper-V and only use Hyper-V hypercalls.