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

[Gleb Natapov]

On Fri, May 29, 2009 at 06:46:47PM +0200, Jan Kiszka wrote:
> 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.
> 
If kvm_vcpu_ioctl(KVM_RUN) is called, but exit happens before interrupt
is injected kvm_run->ready_for_interrupt_injection should be update to
reflect that fact.

--
                        Gleb.