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From: "Pavel Dovgalyuk" <dovgaluk@ispras.ru>
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Date: Wed, 25 Jan 2017 15:27:45 +0300
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Subject: Re: [Qemu-devel] [PATCH v7 03/14] replay: exception replay fix
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To: 'Paolo Bonzini' <pbonzini@redhat.com>, 'Pavel Dovgalyuk' <pavel.dovgaluk@ispras.ru>, qemu-devel@nongnu.org
Cc: kwolf@redhat.com, peter.maydell@linaro.org, mst@redhat.com, jasowang@redhat.com, quintela@redhat.com, kraxel@redhat.com

> From: Paolo Bonzini [mailto:pbonzini@redhat.com]
> On 25/01/2017 12:33, Pavel Dovgalyuk wrote:
> >> From: Paolo Bonzini [mailto:pbonzini@redhat.com]
> >> On 25/01/2017 12:12, Pavel Dovgalyuk wrote:
> >>>> From: Paolo Bonzini [mailto:pbonzini@redhat.com]
> >>>> On 24/01/2017 08:17, Pavel Dovgalyuk wrote:
> >>>>> @@ -451,6 +451,10 @@ static inline bool cpu_handle_exception(CPUState *cpu, int *ret)
> >>>>>  #ifndef CONFIG_USER_ONLY
> >>>>>      } else if (replay_has_exception()
> >>>>>                 && cpu->icount_decr.u16.low + cpu->icount_extra == 0) {
> >>>>> +        /* Break the execution loop in case of running out of TB cache.
> >>>>> +           This is needed to make flushing of the TB cache, because
> >>>>> +           real flush is queued to be executed outside the cpu loop. */
> >>>>> +        cpu->exception_index = EXCP_INTERRUPT;
> >>>>>          /* try to cause an exception pending in the log */
> >>>>>          cpu_exec_nocache(cpu, 1, tb_find(cpu, NULL, 0), true);
> >>>>>          *ret = -1;
> >>>>
> >>>> Why is replay_has_exception() related to be running out of TB cache?
> >>>
> >>> It doesn't.
> >>> Calling tb_find when there is not space in cache causes tb_flush and cpu_loop_exit.
> >>> But execution loop will continue, because there is no reason to break it
> >>> (like setting exception_index).
> >>
> >> What about setting cpu->exit_request?  queue_work_on_cpu calls
> >> qemu_cpu_kick.
> >
> > cpu->exit_request does not checked in this loop.
> > We have to add this checking somewhere then?
> 
> It's checked by cpu_handle_interrupt.  Are you not reaching
> cpu_handle_interrupt then?  Why?

Execution doesn't reach cpu_handle_interrupt, because tb_find 
calls cpu_loop_exit. And the execution loop enters cpu_handle_exception again and again.

Pavel Dovgalyuk