KVM: x86/xen: Add event channel interrupt vector upcall
It turns out that we can't handle event channels *entirely* in userspace
by delivering them as ExtINT, because KVM is a bit picky about when it
accepts ExtINT interrupts from a legacy PIC. The in-kernel local APIC
has to have LVT0 configured in APIC_MODE_EXTINT and unmasked, which
isn't necessarily the case for Xen guests especially on secondary CPUs.
To cope with this, add kvm_xen_get_interrupt() which checks the
evtchn_pending_upcall field in the Xen vcpu_info, and delivers the Xen
upcall vector (configured by KVM_XEN_ATTR_TYPE_UPCALL_VECTOR) if it's
set regardless of LAPIC LVT0 configuration. This gives us the minimum
support we need for completely userspace-based implementation of event
channels.
This does mean that vcpu_enter_guest() needs to check for the
evtchn_pending_upcall flag being set, because it can't rely on someone
having set KVM_REQ_EVENT unless we were to add some way for userspace to
do so manually.
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
diff --git a/arch/x86/kvm/xen.h b/arch/x86/kvm/xen.h
index fb85377..4b32489 100644
--- a/arch/x86/kvm/xen.h
+++ b/arch/x86/kvm/xen.h
@@ -13,6 +13,7 @@
extern struct static_key_false_deferred kvm_xen_enabled;
+int __kvm_xen_has_interrupt(struct kvm_vcpu *vcpu);
int kvm_xen_vcpu_set_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data);
int kvm_xen_vcpu_get_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data);
int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data);
@@ -29,6 +30,14 @@ static inline bool kvm_xen_hypercall_enabled(struct kvm *kvm)
KVM_XEN_HVM_CONFIG_INTERCEPT_HCALL);
}
+static inline int kvm_xen_has_interrupt(struct kvm_vcpu *vcpu)
+{
+ if (static_branch_unlikely(&kvm_xen_enabled.key) &&
+ vcpu->arch.xen.vcpu_info_set && vcpu->kvm->arch.xen.upcall_vector)
+ return __kvm_xen_has_interrupt(vcpu);
+
+ return 0;
+}
/* 32-bit compatibility definitions, also used natively in 32-bit build */
#include <asm/pvclock-abi.h>