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>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b9402d5fa0e90adec2616038f2a5f4211793d956..692c70d6fd02390cbdcfe6ae9f891170603c1f18 100644 (file)
--- 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);