linux-kernel - Re: [PATCHv2 5/7] KVM: SVM: Add VNMI support in inject

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Message-ID: <Yth2eik6usFvC4vW@google.com>
Date:   Wed, 20 Jul 2022 21:41:14 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Santosh Shukla <santosh.shukla@....com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Tom Lendacky <thomas.lendacky@....com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 5/7] KVM: SVM: Add VNMI support in inject_nmi

On Sat, Jul 09, 2022, Santosh Shukla wrote:
> Inject the NMI by setting V_NMI in the VMCB interrupt control. processor
> will clear V_NMI to acknowledge processing has started and will keep the
> V_NMI_MASK set until the processor is done with processing the NMI event.
> 
> Signed-off-by: Santosh Shukla <santosh.shukla@....com>
> ---
> v2:
> - Added WARN_ON check for vnmi pending.
> - use `get_vnmi_vmcb` to get correct vmcb so to inject vnmi.
> 
>  arch/x86/kvm/svm/svm.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 44c1f2317b45..c73a1809a7c7 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -3375,12 +3375,20 @@ static void pre_svm_run(struct kvm_vcpu *vcpu)
>  static void svm_inject_nmi(struct kvm_vcpu *vcpu)
>  {
>  	struct vcpu_svm *svm = to_svm(vcpu);
> +	struct vmcb *vmcb = NULL;
> +
> +	++vcpu->stat.nmi_injections;
> +	if (is_vnmi_enabled(svm)) {
> +		vmcb = get_vnmi_vmcb(svm);
> +		WARN_ON(vmcb->control.int_ctl & V_NMI_PENDING);

Haven't read the spec, but based on the changelog I assume the flag doesn't get
cleared until the NMI is fully delivered.  That means this WARN will fire if a
VM-Exit occurs during delivery as KVM will re-inject the event, e.g. if KVM is
using shadow paging and a #PF handle by KVM occurs during delivery.

> +		vmcb->control.int_ctl |= V_NMI_PENDING;
> +		return;
> +	}
>  
>  	svm->vmcb->control.event_inj = SVM_EVTINJ_VALID | SVM_EVTINJ_TYPE_NMI;
>  	vcpu->arch.hflags |= HF_NMI_MASK;
>  	if (!sev_es_guest(vcpu->kvm))
>  		svm_set_intercept(svm, INTERCEPT_IRET);
> -	++vcpu->stat.nmi_injections;
>  }
>  
>  static void svm_inject_irq(struct kvm_vcpu *vcpu)
> -- 
> 2.25.1
>