On Fri, Nov 7, 2025, at 15:19, Yeoreum Yun wrote:
>> On Thu, Nov 6, 2025, at 10:40, Yeoreum Yun wrote:
>> > apply FEAT_LSUI instruction to emulate deprecated swpX instruction.
>>
>> Can you explain in the changrelog why you do this?
>>
>> In particular, is this a performance optimization or is this required
>> for correctness in some scenario?
>
> I think the main purpose using for this is to "remove the toggling the
> PSTATE.PAN" bit. so that remove some *potential* problem which can
> happen when PAN bit is cleared.
Ok, I see. This should definitely be part of the commit
log for the patch in addition to the cover letter.
> also, though swpb might add some complexity, but swp can get
> a little bit of benifit by removing the ll/sc way and reduce
> the amount of instructions.
This part I think you can ignore in the patch description,
unless there is an additional problem with possibly mixing ll/sc
and lse atomics that you are trying to solve.
Arnd
