Re: [PATCH v2] KVM: Fix simultaneous NMIs

Avi Kivity
2011-09-20T13:56:07Z

On 09/20/2011 04:25 PM, Marcelo Tosatti wrote:
> >
> > @@ -2827,6 +2828,7 @@ static int kvm_vcpu_ioctl_x86_set_mce(struct kvm_vcpu *vcpu,
> > static void kvm_vcpu_ioctl_x86_get_vcpu_events(struct kvm_vcpu *vcpu,
> > struct kvm_vcpu_events *events)
> > {
> > + process_nmi(vcpu);
> > events->exception.injected =
> > vcpu->arch.exception.pending&&
> > !kvm_exception_is_soft(vcpu->arch.exception.nr);
> > @@ -2844,7 +2846,7 @@ static void kvm_vcpu_ioctl_x86_get_vcpu_events(struct kvm_vcpu *vcpu,
> > KVM_X86_SHADOW_INT_MOV_SS | KVM_X86_SHADOW_INT_STI);
> >
> > events->nmi.injected = vcpu->arch.nmi_injected;
> > - events->nmi.pending = vcpu->arch.nmi_pending;
> > + events->nmi.pending = vcpu->arch.nmi_pending != 0;
> > events->nmi.masked = kvm_x86_ops->get_nmi_mask(vcpu);
> > events->nmi.pad = 0;
>
> nmi_queued should also be saved and restored. Not sure if its necessary
> though.
>
> Should at least reset nmi_queued somewhere (set_vcpu_events?).

Did you miss the call to process_nmi()?

We do have a small issue. If we exit during NMI-blocked-by-STI and
nmi_pending == 2, then we lose the second interrupt. Should rarely
happen, since external interrupts never exit in that condition, but it's
a wart.

>
> > @@ -2864,6 +2866,7 @@ static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
> > | KVM_VCPUEVENT_VALID_SHADOW))
> > return -EINVAL;
> >
> > + process_nmi(vcpu);
>
> This should be after nmi fields are set, not before?
>

It's actually to clear queued NMIs in case we set nmi_pending (which
should never happen unless the machine is completely quiet, since it's
asynchronous to the vcpu; same as the IRR).

--
error compiling committee.c: too many arguments to function