KVM: x86: better fix for race between nmi injection and enabling nmi window

Fix race between nmi injection and enabling nmi window in a simpler way.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 10 insertions, 1 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b9402d5fa0e9..692c70d6fd02 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5171,6 +5171,7 @@ 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;
 
@@ -5214,11 +5215,19 @@ 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);