Re: [PATCH 3/3] KVM: Reset PIT irq injection logic when the PIT IRQ is unmasked

[Avi Kivity <avi@redhat.com>]

Marcelo Tosatti wrote:
> On Sun, Jan 04, 2009 at 06:14:45PM +0200, Avi Kivity wrote:
>   
>> While the PIT is masked the guest cannot ack the irq, so the reinject logic
>> will never allow the interrupt to be injected.
>>
>> Fix by resetting the reinjection counters on unmask.
>>
>> Unbreaks Xen.
>>
>> diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
>> index 528daad..d78d430 100644
>> --- a/arch/x86/kvm/i8254.c
>> +++ b/arch/x86/kvm/i8254.c
>> @@ -539,6 +539,16 @@ void kvm_pit_reset(struct kvm_pit *pit)
>>  	pit->pit_state.irq_ack = 1;
>>  }
>>  
>> +static void pit_mask_notifer(struct kvm_irq_mask_notifier *kimn, int mask)
>> +{
>> +	struct kvm_pit *pit = container_of(kimn, struct kvm_pit, mask_notifier);
>> +
>> +	if (!mask) {
>> +		atomic_set(&pit->pit_state.pit_timer.pending, 0);
>> +		pit->pit_state.irq_ack = 1;
>> +	}
>> +}
>>     
>
> I'm not sure about zeroing the counter here. The guest can mask the
> interrupt during normal operation, and in such cases you want the
> pending count to be retained (and reinjected later).
>
> I suppose setting irq_ack to one is enough.
>   

I'm worried about:

- boot guest using local apic timer
- reset
- boot with pit timer
- a zillion interrupts

So at the very least, we need a limiter.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.