linux-kernel - Re: [PATCH] x86/mce: drop cpu_missing since we have more capable mce_missing

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Message-ID: <YYroWYUVJEVKqy+7@zn.tnic>
Date:   Tue, 9 Nov 2021 22:30:01 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Zhaolong Zhang <zhangzl2013@....com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH] x86/mce: drop cpu_missing since we have more capable
 mce_missing_cpus

On Tue, Nov 09, 2021 at 08:44:41PM +0000, Luck, Tony wrote:
> > what do we do with the sysfs knob? It probably is an ABI:
> >
> > /sys/devices/system/machinecheck/machinecheck1/tolerant
> > /sys/devices/system/machinecheck/machinecheck2/tolerant
> 
> $ git grep tolerant -- Documentation/ABI/
> $
> 
> An undocumented ABI! Well, not documented with all the other sysfs bits.
> 
> It does appear in:
> Documentation/x86/x86_64/machinecheck.rst

Yeah, we have some spreading of documentation which is not necessarily
helpful.

> Of course, like a lot of documentation, it isn't accurate. It wasn't
> updated to describe what happens with recoverable errors. Final
> paragraph says:
>
>         Note this only makes a difference if the CPU allows recovery
>         from a machine check exception. Current x86 CPUs generally do
>         not.
>
> Recovery was first introduced in the Nehalem generation which
> ark.intel.com says was launched in Q1'2010. So over a decade.
>
> Choices: 1) Leave the file there, but remove the code that uses the
> value 2) Delete the file too
>
> Option 1 doesn't break any scripts that look for the file, but may
> make people shout louder when they find it no longer does anything.
>
> Option 2 is the more honest approach.

Ack, we can try 2 and see who cries.

-- 
Regards/Gruss,
    Boris.

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