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

[Avi Kivity <avi@redhat.com>]

Marcelo Tosatti wrote:
>>
>> 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.
>>     
>
> Or have a new notifier on kvm_pic_reset, instead of simply acking one
> pending irq? That seems the appropriate place to zero the counter.
>   

Clearing the counter on reset is good, but it doesn't solve the 
underlying problem, which is that there are two separate cases that 
appear to the host as the same thing:

- guest masks irqs, does a lot of work, unmasks irqs
- host deschedules guest, does a lot of work, reschedules guest

Right now we assume any missed interrupts are due to host load.  In the 
reboot case, that's clearly wrong, but that is only an example.  Maybe 
we can use preempt notifiers to detect whether the timer tick happened 
while the guest was scheduled or not.

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