KVM: SVM: suppress unnecessary NMI singlestep on GIF=0 and nested exit

enable_nmi_window is supposed to be a no-op if we know that we'll see
a VM exit by the time the NMI window opens. This commit adds two more
cases:

* We intercept stgi so we don't need to singlestep on GIF=0.

* We emulate nested vmexit so we don't need to singlestep when nested
  VM exit is required.

Signed-off-by: Ladi Prosek <lprosek@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 5973379..03df7c1 100644 (file)
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -4678,6 +4678,12 @@ static void enable_nmi_window(struct kvm_vcpu *vcpu)
            == HF_NMI_MASK)
                return; /* IRET will cause a vm exit */
 
+       if ((svm->vcpu.arch.hflags & HF_GIF_MASK) == 0)
+               return; /* STGI will cause a vm exit */
+
+       if (svm->nested.exit_required)
+               return; /* we're not going to run the guest yet */
+
        /*
         * Something prevents NMI from been injected. Single step over possible
         * problem (IRET or exception injection or interrupt shadow)