From: Gleb Natapov <gleb@xxxxxxxxxx>
Fix race between nmi injection and enabling nmi window in a simpler way.
Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
v2: document benign race.
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index bfd7763..e6bdc14 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5152,6 +5152,7 @@ static void kvm_put_guest_xcr0(struct kvm_vcpu *vcpu)
static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
{
int r;
+ bool nmi_pending;
bool req_int_win = !irqchip_in_kernel(vcpu->kvm) &&
vcpu->run->request_interrupt_window;
@@ -5197,11 +5198,19 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
if (unlikely(r))
goto out;
+ /*
+ * An NMI can be injected between local nmi_pending read and
+ * vcpu->arch.nmi_pending read inside inject_pending_event().
+ * But in that case, KVM_REQ_EVENT will be set, which makes
+ * the race described above benign.
+ */
+ nmi_pending = ACCESS_ONCE(vcpu->arch.nmi_pending);
+
if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win) {
inject_pending_event(vcpu);
/* enable NMI/IRQ window open exits if needed */
- if (vcpu->arch.nmi_pending)
+ if (nmi_pending)
kvm_x86_ops->enable_nmi_window(vcpu);
else if (kvm_cpu_has_interrupt(vcpu) || req_int_win)
kvm_x86_ops->enable_irq_window(vcpu);
--
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