On Thu, 2020-11-26 at 11:10 +0000, David Woodhouse wrote:
> 
> > whether or not there's an IRQ in the
> > LAPIC should be irrelevant when deciding to exit to userspace.  Note, the
> > reinjection check covers vcpu->arch.interrupt.injected for the case where LAPIC
> > is in userspace.
> > 
> >         return kvm_arch_interrupt_allowed(vcpu) &&
> >                (!lapic_in_kernel(vcpu) || !kvm_cpu_has_extint(vcpu)) &&
> >                !kvm_event_needs_reinjection(vcpu) &&
> >                kvm_cpu_accept_dm_intr(vcpu);
> > }
> 
> Makes sense. I'm putting this version through some testing and will
> post it later...

Hm, that survived enough test iterations to persuade me to post it, but
then seems to have fallen over later. I'm reverting to the
kvm_cpu_has_injectable_intr() version to leave that one running too and
be sure it's gone in that.

Without either patch it's 100% repeatable, and will happen as soon as
the 'noapic' guest enabled lapic timer interrupts. I'm not sure I see
why your version would simply make it less frequent...