Re: [PATCH v2] KVM: x86: Inject pending interrupt even if pending nmi exist

["Radim Krčmář" <rkrcmar@redhat.com>]

2016-03-23 19:22+0100, Paolo Bonzini:
> On 23/03/2016 18:21, Radim Krčmář wrote:
>> NMIs are latched (queue length 1) and therefore cannot be pending after
>> an injection.  I think we want to do it unconditionally.
> 
> If that is right, process_nmi would be the place where you'd limit the
> queue to 1.

You are right.

I think we can always limit the queue to 1:
process_nmi is from 7460fb4a3400 ("KVM: Fix simultaneous NMIs") and the
commit message explains
  If simultaneous NMIs happen, we're supposed to queue the second and
  next (collapsing them), but currently we sometimes collapse the second
  into the first.

I think that hardware coalesces all NMIs that arrive within one
instruction (NMI is delivered at instruction boundaries)
and one NMI is sufficient anyway (all events that triggered NMIs are
going to be handled in the first one and the second one is for nothing),
so reasons behind "supposed to" elude me.

We could overhaul NMI handling much more at that point, but it's safer
to keep it this way as there aren't major bugs. :)