Re: [Qemu-devel] [PATCH v7 03/14] replay: exception replay fix

["Pavel Dovgalyuk" <dovgaluk@ispras.ru>]

> From: Paolo Bonzini [mailto:pbonzini@redhat.com]
> On 25/01/2017 13:27, Pavel Dovgalyuk wrote:
> >> 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.
> 
> Perhaps tb_gen_code should set cpu->exception_index before calling
> cpu_loop_exit.

Maybe it would be better, because tb_gen_code is called in many other paths.
I'll fix the patch.

Pavel Dovgalyuk