Re: [PATCHv3 5/8] KVM: SVM: Add VNMI support in inject_nmi

["Shukla, Santosh" <santosh.shukla@amd.com>]

Hi Maciej,

On 8/11/2022 2:54 AM, Maciej S. Szmigiero wrote:
> 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@amd.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.
> 

Not sure if I understood the case fully.. so trying to sketch scenario here -
if nmi_l1_to_l2 is true then event is coming from EVTINJ. .which could
be one of following case -
1) L0 (vnmi enabled) and L1 (vnmi disabled)
2) L0 & L1 both vnmi disabled.

In both cases the vnmi check will fail for L1 and execution path
will fall back to default - right?

Thanks,
Santosh

> 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