On Tue, May 28, 2013 at 06:33:39PM +0200, Paolo Bonzini wrote:
> Il 28/05/2013 17:00, Gleb Natapov ha scritto:
> > On Tue, May 28, 2013 at 03:48:58PM +0200, Paolo Bonzini wrote:
> >> Il 28/05/2013 14:56, Gleb Natapov ha scritto:
> >>>>> else
> >>>>> vcpu->arch.mp_state = KVM_MP_STATE_INIT_RECEIVED;
> >>>>> }
> >>>>> - if (test_and_clear_bit(KVM_APIC_SIPI, &apic->pending_events) &&
> >>>>> + /*
> >>>>> + * Note that we may get another INIT+SIPI sequence right here; process
> >>>>> + * the INIT first. Assumes that there are only KVM_APIC_INIT/SIPI.
> >>>>> + */
> >>>>> + if (cmpxchg(&apic->pending_events, KVM_APIC_SIPI, 0) == KVM_APIC_SIPI &&
> >>>>> vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED) {
> >>> Because pending_events can be INIT/SIPI at this point and it should be
> >>> interpreted as: do SIPI and ignore INIT (atomically).
> >>
> >> My patch does "do another INIT (which will have no effect) and do SIPI
> >> after that INIT", which is different but has almost the same effect.
> >> If pending_events is INIT/SIPI, it ignores the SIPI for now and lets
> >> the next iteration of kvm_apic_accept_events do both. The difference
> >> would be that in a carefully-timed sequence of interrupts
> >>
> > You assume that the next processing will actually happen, but this is
> > not necessary the case.
>
> Why not? The INIT and SIPI that have just been sent have kicked the
> VCPU again.
>
kick is a nop if vcpu thread is not in a halt or in a guest.
> >> But then, there's another way to mask INITs in the wait-for-SIPI
> >> state. Considering that KVM_MP_STATE_INIT_RECEIVED is really a
> >> wait-for-SIPI, you can do:
> >>
> > Haven't checked it for races (especially races between multiple CPUS
> > sending INIT), but looks more complicated to me.
>
> Ok, let's go with yours.
>
> Paolo
--
Gleb.
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