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Re: [PATCH for-4.21 1/2] x86/AMD: avoid REP MOVSB for Zen3/4
- To: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 8 Oct 2025 18:06:20 +0200
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- Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Jason Andryuk <jason.andryuk@xxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>
- Delivery-date: Wed, 08 Oct 2025 16:06:25 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 08.10.2025 13:20, Roger Pau Monné wrote:
> On Mon, Sep 29, 2025 at 07:35:53PM -0400, Jason Andryuk wrote:
>> On 2025-09-25 08:18, Teddy Astie wrote:
>>> Le 25/09/2025 à 12:48, Jan Beulich a écrit :
>>>> Along with Zen2 (which doesn't expose ERMS), both families reportedly
>>>> suffer from sub-optimal aliasing detection when deciding whether REP MOVSB
>>>> can actually be carried out the accelerated way. Therefore we want to
>>>> avoid its use in the common case (memset(), copy_page_hot()).
>>>
>>> s/memset/memcpy (memset probably uses rep stosb which is not affected IIUC)
>>>
>>>>
>>>> Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>
>> With Teddy's suggested change:
>>
>> Reviewed-by: Jason Andryuk <jason.andryuk@xxxxxxx>
>
> Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
May I ask for a release-ack here, seeing that it alters behavior that went in
close before the freeze?
Jan
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