Il 30/05/2013 03:20, Gleb Natapov ha scritto:
> 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 the KVM_REQ_EVENT request will be caught at:
if (vcpu->mode == EXITING_GUEST_MODE || vcpu->requests
|| need_resched() || signal_pending(current)) {
vcpu->mode = OUTSIDE_GUEST_MODE;
smp_wmb();
local_irq_enable();
preempt_enable();
r = 1;
goto cancel_injection;
}
and the entry will be canceled.
Paolo
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