Re: [PATCH v7 7/8] target/arm: handle the WFE trap case

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

Peter Maydell <peter.maydell@linaro.org> writes:

> On Mon, 15 Jun 2026 at 11:56, Alex Bennée <alex.bennee@linaro.org> wrote:
>>
>> Peter Maydell <peter.maydell@linaro.org> writes:
>>
>> > On Fri, 29 May 2026 at 09:29, Alex Bennée <alex.bennee@linaro.org> wrote:
>> >>
>> >> Now WFE can actually suspend on A-profile we also need to handle when
>> >> its trapped. To do this we need to pass the instruction size so we can
>> >> deal with the is_16bit syndrome encoding.
>> >>
>> >> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
>> >> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>> >
>> > Doesn't this need to go earlier in the patchset? Otherwise there's
>> > a point where WFE can go to sleep but doesn't honour the trap bit.
>>
>> Hmm - the way I read the description was we would only trap if we were
>> going to sleep. Pre 6/8 we never sleep so we can't trap.
>
> Yes, that's the point. The guarantee we have to uphold with
> the trap bits is "if the WFE would actually go to sleep, then
> we need to take the trap".
>
> - before this patchset: we never sleep, so never need to trap
> - after patch 6: we can sleep, but we incorrectly won't trap
> - after this patch: we can sleep and will trap
>
> So there's a window in this patchseries (after 6 but before 7)
> where we don't do the right thing.

OK I'll squash the two patches together.

>
> -- PMM

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro