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

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Message-ID: <a18658e5-3788-b3f3-db0d-1ab29ea89f88@amd.com>
Date:   Sat, 14 Oct 2023 15:46:14 +0530
From:   Santosh Shukla <santosh.shukla@....com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: SVM: Don't intercept IRET when injecting NMI and
 vNMI is enabled



On 10/10/2023 8:16 PM, Sean Christopherson wrote:
> 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;
>  }
>  
>

quick testing worked fine, KUT test ran fine and tested for non-nested mode so far.
Will do more nested testing and share the feedback.

Thanks,
Santosh

> base-commit: 86701e115030e020a052216baa942e8547e0b487