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

[Maciej S. Szmigiero]

On 24.08.2022 14:13, Shukla, Santosh wrote:
> 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@xxxxxxx>
> > > ---
> > > 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)

As far as I can see in this case:
is_vnmi_enabled() returns whether VMCB02's int_ctl has V_NMI_ENABLE bit set.

This field in VMCB02 comes from nested_vmcb02_prepare_control() which
in the !nested_vnmi_enabled() case (L1 is not using vNMI) copies these bits
from VMCB01:
> int_ctl_vmcb01_bits |= (V_NMI_PENDING | V_NMI_ENABLE | V_NMI_MASK);

So in this case (L0 uses vNMI) V_NMI_ENABLE will be set in VMCB01, right?

This bit will then be copied to VMCB02 so re-injection will attempt to use
vNMI instead of EVTINJ.

> 2) L0 & L1 both vnmi disabled.

This case is ok.

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

Thanks,
Maciej