KVM: x86/xen: Add kvm_xen_enabled static key
The code paths for Xen support are all fairly lightweight but if we hide
them behind this, they're even *more* lightweight for any system which
isn't actually hosting Xen guests.
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 673dcc6..ffc4ab3 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7988,6 +7988,7 @@ void kvm_arch_exit(void)
kvm_mmu_module_exit();
free_percpu(user_return_msrs);
kmem_cache_destroy(x86_fpu_cache);
+ WARN_ON(static_branch_unlikely(&kvm_xen_enabled.key));
}
static int __kvm_vcpu_halt(struct kvm_vcpu *vcpu, int state, int reason)
@@ -10581,6 +10582,7 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
kfree(srcu_dereference_check(kvm->arch.pmu_event_filter, &kvm->srcu, 1));
kvm_mmu_uninit_vm(kvm);
kvm_page_track_cleanup(kvm);
+ kvm_xen_destroy_vm(kvm);
kvm_hv_destroy_vm(kvm);
}
diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index b52549f..7d03d91 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -16,6 +16,8 @@
#include "trace.h"
+DEFINE_STATIC_KEY_DEFERRED_FALSE(kvm_xen_enabled, HZ);
+
int kvm_xen_write_hypercall_page(struct kvm_vcpu *vcpu, u64 data)
{
struct kvm *kvm = vcpu->kvm;
@@ -93,10 +95,25 @@ int kvm_xen_hvm_config(struct kvm *kvm, struct kvm_xen_hvm_config *xhc)
xhc->blob_size_32 || xhc->blob_size_64))
return -EINVAL;
+ mutex_lock(&kvm->lock);
+
+ if (xhc->msr && !kvm->arch.xen_hvm_config.msr)
+ static_branch_inc(&kvm_xen_enabled.key);
+ else if (!xhc->msr && kvm->arch.xen_hvm_config.msr)
+ static_branch_slow_dec_deferred(&kvm_xen_enabled);
+
memcpy(&kvm->arch.xen_hvm_config, xhc, sizeof(*xhc));
+
+ mutex_unlock(&kvm->lock);
return 0;
}
+void kvm_xen_destroy_vm(struct kvm *kvm)
+{
+ if (kvm->arch.xen_hvm_config.msr)
+ static_branch_slow_dec_deferred(&kvm_xen_enabled);
+}
+
static int kvm_xen_hypercall_set_result(struct kvm_vcpu *vcpu, u64 result)
{
kvm_rax_write(vcpu, result);
diff --git a/arch/x86/kvm/xen.h b/arch/x86/kvm/xen.h
index 28e9c98..ec3d8f6 100644
--- a/arch/x86/kvm/xen.h
+++ b/arch/x86/kvm/xen.h
@@ -9,14 +9,20 @@
#ifndef __ARCH_X86_KVM_XEN_H__
#define __ARCH_X86_KVM_XEN_H__
+#include <linux/jump_label_ratelimit.h>
+
+extern struct static_key_false_deferred kvm_xen_enabled;
+
int kvm_xen_hypercall(struct kvm_vcpu *vcpu);
int kvm_xen_write_hypercall_page(struct kvm_vcpu *vcpu, u64 data);
int kvm_xen_hvm_config(struct kvm *kvm, struct kvm_xen_hvm_config *xhc);
+void kvm_xen_destroy_vm(struct kvm *kvm);
static inline bool kvm_xen_hypercall_enabled(struct kvm *kvm)
{
- return kvm->arch.xen_hvm_config.flags &
- KVM_XEN_HVM_CONFIG_INTERCEPT_HCALL;
+ return static_branch_unlikely(&kvm_xen_enabled.key) &&
+ (kvm->arch.xen_hvm_config.flags &
+ KVM_XEN_HVM_CONFIG_INTERCEPT_HCALL);
}
#endif /* __ARCH_X86_KVM_XEN_H__ */