linux-kernel - Re: [PATCH AUTOSEL 5.15 11/12] x86/barrier: Do not serialize MSR accesses on AMD

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Message-ID: <Z0kJHvesUl6xJkS7@sashalap>
Date: Thu, 28 Nov 2024 19:21:50 -0500
From: Sasha Levin <sashal@...nel.org>
To: Borislav Petkov <bp@...en8.de>
Cc: linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
	x86@...nel.org, puwen@...on.cn, seanjc@...gle.com,
	kim.phillips@....com, jmattson@...gle.com, babu.moger@....com,
	peterz@...radead.org, rick.p.edgecombe@...el.com, brgerst@...il.com,
	ashok.raj@...el.com, mjguzik@...il.com, jpoimboe@...nel.org,
	nik.borisov@...e.com, aik@....com, vegard.nossum@...cle.com,
	daniel.sneddon@...ux.intel.com, acdunlap@...gle.com,
	Erwan Velu <erwanaliasr1@...il.com>, pavel@...x.de
Subject: Re: [PATCH AUTOSEL 5.15 11/12] x86/barrier: Do not serialize MSR
 accesses on AMD

On Thu, Nov 28, 2024 at 05:43:10PM +0100, Borislav Petkov wrote:
>On Thu, Nov 28, 2024 at 10:52:44AM -0500, Sasha Levin wrote:
>> You've missed the 5.10 mail :)
>
>You mean in the flood? ;-P

Suggestions welcome... I don't really insist on a massive flood and was
mostly following what was the convention when I started doing this work.

I thought about cutting it down to one mail per commit, but OTOH I had
folks complain often enough that they missed a mail or that it wasn't
obvious enough.

>> Pavel objected to it so I've dropped it: https://lore.kernel.org/all/Zbli7QIGVFT8EtO4@sashalap/
>
>So we're not backporting those anymore? But everything else? :-P

It was dropped from everywhere. The reason it ended up in 6.6 was
because your AMD friends requested it:
https://lore.kernel.org/all/2024022146-chunk-fencing-1e8f@gregkh/

>And 5.15 has it already...

It might be all those thanksgiving drinks, but I can't find it in
5.15... I see it was part of 6.7.6 and 6.6.18, but nothing older.

>Frankly, with the amount of stuff going into stable, I see no problem with
>backporting such patches. Especially if the people using stable kernels will
>end up backporting it themselves and thus multiply work. I.e., Erwan's case.

The stable kernel rules allow for "notable" performance fixes, and we
already added it to 6.6. No objection to adding it to older kernels...

Happy to do it after the current round of releases goes out.

-- 
Thanks,
Sasha