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

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Date:   Fri, 29 Jul 2022 11:36:28 +0530
From:   "Shukla, Santosh" <santosh.shukla@....com>
To:     Sean Christopherson <seanjc@...gle.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

Hi Sean,

On 7/21/2022 3:11 AM, Sean Christopherson wrote:
> 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.
> 

Right,.


For the above scenario i.e.. if VMEXIT happens during delivery of virtual NMI
then EXITINTINFO will be set accordingly and V_NMI_MASK is saved as 0.
hypervisor will re-inject event in next VMRUN.

I just wanted to track above scenario,. I will replace it with pr_debug().

Thanks,
Santosh


>> +		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
>>