Re: [PATCH 1/2] KVM: nSVM: Set NMI_VECTOR in synthesized NMI exit_int_info

[Sean Christopherson <seanjc@google.com>]

I'm mildly disappointed you didn't go with:

  KVM: nSVM: Really synthesize correct EXITINTINFO on vmexit

:-D

On Wed, Oct 28, 2026, Jim Mattson wrote:
> Include NMI_VECTOR (2) in the vector field when synthesizing exit_int_info
> for a pending injected NMI in nested_save_pending_event_to_vmcb12(),
> matching nested VMX's idt_vectoring_info_field synthesis and the APM.
> 
> Per AMD's APM (Vol. 2, "Intercepts During IDT Interrupt Delivery", Figure
> "EXITINTINFO" and Table "Guest Exception or Interrupt Types", and "Event
> Injection"), bits 7:0 of EXITINTINFO hold the 8-bit IDT vector of the
> interrupt or exception, and injected events are recorded in EXITINTINFO as
> though they had occurred normally in the guest.  Although hardware ignores
> EVENTINJ.VECTOR on VMRUN when TYPE is NMI, EXITINTINFO records vector 2
> (#NMI) if a #VMEXIT occurs during NMI delivery.
> 
> Commit 36e2e98363e6 ("KVM: nSVM: synthesize correct EXITINTINFO on vmexit")
> replaced the raw copy of vmcb02->control.exit_int_info (where hardware
> populates vector 2) with nested_vmcb_save_pending_event(), now
> nested_save_pending_event_to_vmcb12(), which sets only SVM_EVTINJ_VALID |
> SVM_EVTINJ_TYPE_NMI and leaves the vector field as 0.  As a result, L1
> hypervisors that check EXITINTINFO.VECTOR == 2 for NMIs (e.g. FreeBSD's
> bhyve) or inspect the vector field of exit_int_info observe an invalid
> vector 0 on nested #VMEXIT.
> 
> Fixes: 36e2e98363e6 ("KVM: nSVM: synthesize correct EXITINTINFO on vmexit")
> Signed-off-by: Jim Mattson <jmattson@google.com>
> ---
>  arch/x86/kvm/svm/nested.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index af0ef678433d..9b62113f0cf6 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -673,7 +673,7 @@ static void nested_save_pending_event_to_vmcb12(struct vcpu_svm *svm,
>  		}
>  
>  	} else if (vcpu->arch.nmi_injected) {
> -		exit_int_info = SVM_EVTINJ_VALID | SVM_EVTINJ_TYPE_NMI;
> +		exit_int_info = SVM_EVTINJ_VALID | SVM_EVTINJ_TYPE_NMI | NMI_VECTOR;
>  
>  	} else if (vcpu->arch.interrupt.injected) {
>  		nr = vcpu->arch.interrupt.nr;
> 
> base-commit: dea4f6380f4ec96e8f3b0aaf2343764bd0d25ef4
> -- 
> 2.56.0.307.g5fe7bd680c-goog
>