Re: [Qemu-devel] MTTCG External Halt

[Alex Bennée]

Alistair Francis <address@hidden> writes:

> On Wed, Jan 31, 2018 at 12:32 PM, Alex Bennée <address@hidden> wrote:
>>
>> Alistair Francis <address@hidden> writes:
>>
>>> On Tue, Jan 30, 2018 at 8:26 PM, Paolo Bonzini <address@hidden> wrote:
>>>> On 30/01/2018 18:56, Alistair Francis wrote:
>>>>>
>>>>> I don't have a good solution though, as setting CPU_INTERRUPT_RESET
>>>>> doesn't help (that isn't handled while we are halted) and
>>>>> async_run_on_cpu()/run_on_cpu() doesn't reliably reset the CPU when we
>>>>> want.
>>>>>
>>>>> I've ever tried pausing all CPUs before reseting the CPU and them
>>>>> resuming them all but that doesn't seem to to work either.
>>>>
>>>> async_safe_run_on_cpu would be like async_run_on_cpu, except that it
>>>> takes care of stopping all other CPUs while the function runs.
>>>>
>>>>> Is there
>>>>> anything I'm missing? Is there no reliable way to reset a CPU?
>>>>
>>>> What do you mean by reliable?  Executing no instruction after the one
>>>> you were at?
>>>
>>> The reset is called by a GPIO line, so I need the reset to be called
>>> basically as quickly as the GPIO line changes. The async_ and
>>> async_safe_ functions seem to not run quickly enough, even if I run a
>>> process_work_queue() function afterwards.
>>>
>>> Is there a way to kick the CPU to act on the async_*?
>>
>> Define quickly enough? The async_(safe) functions kick the vCPUs so they
>> will all exit the run loop as they enter the next TB (even if they loop
>> to themselves).
>
> We have a special power controller CPU that wakes all the CPUs up and
> at boot the async_* functions don't wake the CPUs up. If I just use
> the cpu_rest() function directly everything starts fine (but then I
> hit issues later).
>
> If I forcefully run process_queued_cpu_work() then I can get the CPUs
> up, but I don't think that is the right solution.
>
>>
>> From an external vCPUs point of view those extra instructions have
>> already executed. If the resetting vCPU needs them to have reset by the
>> time it executes it's next instruction it should either cpu_loop_exit at
>> that point or ensure it is the last instruction in it's TB (which is
>> what we do for the MMU flush cases in ARM, they all end the TB at that
>> point).
>
> cpu_loop_exit() sounds like it would help, but as I'm not in the CPU
> context it just seg faults.

What context are you in? gdb-stub does have to something like this.

>
> Alistair
>
>>
>>
>>>
>>> Thanks,
>>> Alistair
>>>
>>>>
>>>> Paolo
>>>>
>>
>>
>> --
>> Alex Bennée
>>


--
Alex Bennée