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

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Date:   Wed, 16 Feb 2022 18:41:58 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Borislav Petkov <bp@...en8.de>, Jue Wang <juew@...gle.com>
CC:     "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

> 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"?

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

-Tony