linux-kernel - Re: [PATCH 1/1] x86/mm: Forbid the zero page once it has uncorrectable errors

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Message-ID: <3720f7d9-a4f3-214c-1dea-f8ffc837c1da@intel.com>
Date:   Wed, 20 Apr 2022 06:39:02 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Qiuxu Zhuo <qiuxu.zhuo@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Tony Luck <tony.luck@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Naoya Horiguchi <naoya.horiguchi@....com>
Cc:     "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "open list:HWPOISON MEMORY FAILURE HANDLING" <linux-mm@...ck.org>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] x86/mm: Forbid the zero page once it has
 uncorrectable errors

On 4/20/22 14:00, Qiuxu Zhuo wrote:
> Accessing to the zero page with uncorrectable errors causes unexpected
> machine checks. So forbid the zero page from being used by user-space
> processes once it has uncorrectable errors. Processes that have already
> mapped the zero page with uncorrectable errors will get killed once they
> access to it. New processes will not use the zero page.

There are lots of pages which are entirely fatal if they have
uncorrectable errors.  On my laptop, if there were an error, there is a
0.00000596% chance it will be in the zero page.

Why is this worth special casing this one page?