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

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Date:   Wed, 16 Feb 2022 19:52:58 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Jue Wang <juew@...gle.com>, "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "patches@...ts.linux.dev" <patches@...ts.linux.dev>
Subject: Re: [PATCH] x86/mce: Add workaround for SKX/CLX/CPX spurious machine
 checks

On Wed, Feb 16, 2022 at 06:41:58PM +0000, Luck, Tony wrote:
> > 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.
> 
> Is this a case of "perfect is the enemy of good enough"?

Well, you guys sounded like this happens left and right...

> It is a rare scenario (only a pain point for Jue because Google has
> billions and billions of cores running this code). You need:
>
> 1) An uncorrected error
> 2) That error must be in first cache line of a page
> 3) Kernel must execute page_copy from the page immediately before that page
> 
> 	When all three happen, kernel crashes because we don't
> 	have a recover path from kernel page_copy

You should've lead with that - this is basically one of those "under a
complex set of conditions" things.

Anything against me adding them to the commit message?

-- 
Regards/Gruss,
    Boris.

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