linux-kernel - Re: [PATCHv3 5/8] KVM: SVM: Add VNMI support in inject

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Message-ID: <bf9e8a9c-5172-b61a-be6e-87a919442fbd@maciej.szmigiero.name>
Date:   Wed, 10 Aug 2022 23:24:13 +0200
From:   "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
To:     Santosh Shukla <santosh.shukla@....com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Tom Lendacky <thomas.lendacky@....com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, mlevitsk@...hat.com
Subject: Re: [PATCHv3 5/8] KVM: SVM: Add VNMI support in inject_nmi

On 10.08.2022 08:12, 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>
> ---
> v3:
> - Removed WARN_ON check.
> 
> 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 | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index e260e8cb0c81..8c4098b8a63e 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -3479,7 +3479,14 @@ 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;
>   
> +	if (is_vnmi_enabled(svm)) {

I guess this should be "is_vnmi_enabled(svm) && !svm->nmi_l1_to_l2"
since if nmi_l1_to_l2 is true then the NMI to be injected originally
comes from L1's VMCB12 EVENTINJ field.

As you said in the cover letter, this field has different semantics
than vNMI - specifically, it should allow injecting even if L2 is in
NMI blocking state (it's then up to L1 to keep track of NMI injectability
for its L2 guest - so L0 should be transparently injecting it when L1
wants so).

> +		vmcb = get_vnmi_vmcb(svm);
> +		vmcb->control.int_ctl |= V_NMI_PENDING;
> +		++vcpu->stat.nmi_injections;
> +		return;
> +	}
>   	svm->vmcb->control.event_inj = SVM_EVTINJ_VALID | SVM_EVTINJ_TYPE_NMI;
>   
>   	if (svm->nmi_l1_to_l2)

Thanks,
Maciej