linux-kernel - Re: [PATCH] x86/mce: Add workaround for SKX/CLX/CPX spurious machine checks

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Message-ID: <Yg08Uhg0fZ9xZuP2@zn.tnic>
Date:   Wed, 16 Feb 2022 19:02:58 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Jue Wang <juew@...gle.com>
Cc:     "Luck, Tony" <tony.luck@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, patches@...ts.linux.dev
Subject: Re: [PATCH] x86/mce: Add workaround for SKX/CLX/CPX spurious machine
 checks

On Wed, Feb 16, 2022 at 07:50:24AM -0800, Jue Wang wrote:
> My slight reservation is that this suggests all use cases of "REP;
> MOVS*" must take the _ASM_EXTABLE_ form, which is not possible;
> considering "REP; MOVS*" can be exercised from any user space program.

Well, we could try to decode the instructions around rIP when the #MC
is raised and see what caused the MCE and perhaps pick apart which insn
caused it, is it accessing behind the buffer boundaries, etc.

> If there is a way to get all users of "REP; MOVS*" to use
> copy_mc_enhanced_fast_string, this could work. I am not sure this is
> possible.

Yeah, no, this is for the copy to user direction only.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette