Il 30/05/2013 08:01, Gleb Natapov ha scritto:
> On Thu, May 30, 2013 at 07:41:05AM +0200, Paolo Bonzini wrote:
>> 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.
I was wrong: we exit immediately because state is
KVM_MP_STATE_INIT_RECEIVED. But then...
> But vcpu may be in non running state so we will not get here.
... vcpu_enter_guest will return 1 and __vcpu_run goes around the while
loop once more (modulo pending signals of course).
On the next iteration __vcpu_run will call kvm_vcpu_block, which calls
kvm_arch_vcpu_runnable. kvm_arch_vcpu_runnable returns true because
kvm_apic_has_events(vcpu) is also true. This will set KVM_REQ_UNHALT,
call kvm_apic_accept_events again and do the INIT+SIPI.
Paolo
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