Re: [PATCH] KVM: SVM: Don't intercept IRET when injecting NMI and vNMI is enabled

[Sean Christopherson <seanjc@google.com>]

On Tue, Oct 10, 2023, Maxim Levitsky wrote:
> У пн, 2023-10-09 у 14:29 -0700, Sean Christopherson пише:
> > Note, per the APM, hardware sets the BLOCKING flag when software directly
> > directly injects an NMI:
> > 
> >   If Event Injection is used to inject an NMI when NMI Virtualization is
> >   enabled, VMRUN sets V_NMI_MASK in the guest state.
> 
> I think that this comment is not needed in the commit message. It describes
> a different unrelated concern and can be put somewhere in the code but
> not in the commit message.

I strongly disagree, this blurb in the APM directly affects the patch.  If hardware
didn't set V_NMI_MASK, then the patch would need to be at least this:

--
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index b7472ad183b9..d34ee3b8293e 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3569,8 +3569,12 @@ static void svm_inject_nmi(struct kvm_vcpu *vcpu)
 	if (svm->nmi_l1_to_l2)
 		return;
 
-	svm->nmi_masked = true;
-	svm_set_iret_intercept(svm);
+	if (is_vnmi_enabled(svm)) {
+		svm->vmcb->control.int_ctl |= V_NMI_BLOCKING_MASK;
+	} else {
+		svm->nmi_masked = true;
+		svm_set_iret_intercept(svm);
+	}
 	++vcpu->stat.nmi_injections;
 }
 

base-commit: 86701e115030e020a052216baa942e8547e0b487
-- 

and maybe even more to deal with canceled injection.