Re: [PATCH 2/4] target/hppa: defer hppa_ptlbe until CPU starts running

["Alex Bennée" <alex.bennee@linaro.org>]

"Nicholas Piggin" <npiggin@gmail.com> writes:

> On Wed Feb 26, 2025 at 5:38 AM AEST, Richard Henderson wrote:
>> On 2/25/25 11:33, Richard Henderson wrote:
>>> On 2/25/25 10:46, Alex Bennée wrote:
>>>> @@ -191,7 +199,7 @@ static void hppa_cpu_realizefn(DeviceState *dev, Error **errp)
>>>>           cpu->alarm_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
>>>>                                           hppa_cpu_alarm_timer, cpu);
>>>> -        hppa_ptlbe(&cpu->env);
>>>> +        async_run_on_cpu(cs, hppa_clear_ptlbe, RUN_ON_CPU_HOST_PTR(&cpu->env));
>>> 
>>> Nack, this is emulation of hardware, not softmmu.
>>
>> Hmm.  I see what you're thinking about though: this function, after resetting the data 
>> structures associated with the hardware emulation, also calls the softmmu flush.
>>
>> If we absolutely need to do so, I suppose delaying the hardware emulation flush to the 
>> work queue isn't the worst solution.  This is where the hppa patch is more correct than 
>> the ppc patch which completely eliminated the hardware emulation flush.
>
> Could we expose a function that performs the hardware state reset,
> and leave the TCG flushing to the TCG CPU reset?

I did consider that - but the function is also called from helpers at
which point you also do need to flush the softmmu TLB. However someone
with better knowledge of the architecture might be able to do a slightly
more refined flush (individual pages or mmuidxs) in those cases.

>
> Thanks,
> Nick

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro