[Qemu-devel] Re: Lost interrupts with upstream KVM

[Jan Kiszka]

Gleb Natapov wrote:
> On Fri, May 29, 2009 at 04:52:41PM +0200, Jan Kiszka wrote:
>> Gleb Natapov wrote:
>>> On Fri, May 29, 2009 at 10:23:24AM +0200, Jan Kiszka wrote:
>>>> Hi Gleb,
>>>>
>>>> with latest kernel modules, namely beginning with 6bc0a1a235 (Remove
>>>> irq_pending bitmap), I'm loosing interrupts with upstream's KVM support.
>>>> After some bisecting, hair-pulling and a bit meditation I added a
>>>> WARN_ON(kvm_cpu_has_interrupt(vcpu)) to kvm_vcpu_ioctl_interrupt, and it
>>>> actually triggered right before the guest got stuck.
>>>>
>>>> This didn't trigger with qemu-kvm (and -no-kvm-irqchip) yet but, on the
>>>> other hand, I currently do not see a potential bug in upstream's
>>>> kvm_arch_pre_run. Could you have a look if you can reproduce,
>>>> specifically if this isn't a KVM kernel issue in the end?
>>>>
>>> In kvm_cpu_exec() after calling kvm_arch_pre_run() env->exit_request is
>>> tested and function can exit without calling kvm_vcpu_ioctl(KVM_RUN).
>>> Can you check if this what happens in your case?
>> This path is executed quite frequently here. No obvious correlation with
>> the lost IRQ.
>>
> If kvm_arch_pre_run() injected interrupt kvm_vcpu_ioctl(KVM_RUN) have to
> be executed before injecting another interrupt, so if on the fist call
> of kvm_cpu_exec() kvm_arch_pre_run() injected interrupt, but
> kvm_vcpu_ioctl(KVM_RUN) was not executed because of env->exit_request
> and on the next kvm_cpu_exec() other interrupt is injected the previous
> one will be lost.

...and kvm_run->ready_for_interrupt_injection is not updated either in
that case, right? That makes be wonder if KVM_INTERRUPT shouldn't better
return an error in case the queue is full already.

Jan

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