linux-kernel - Re: [PATCH v2 1/2] x86/split_lock: Make life miserable for split lockers

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Message-ID: <20220317111305.GB2237@amd>
Date:   Thu, 17 Mar 2022 12:13:05 +0100
From:   Pavel Machek <pavel@...x.de>
To:     Tony Luck <tony.luck@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Fenghua Yu <fenghua.yu@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, patches@...ts.linux.dev
Subject: Re: [PATCH v2 1/2] x86/split_lock: Make life miserable for split
 lockers

Hi!

> In https://lore.kernel.org/all/87y22uujkm.ffs@tglx/ Thomas
> said:
> 
>   Its's simply wishful thinking that stuff gets fixed because of a
>   WARN_ONCE(). This has never worked. The only thing which works is to
>   make stuff fail hard or slow it down in a way which makes it annoying
>   enough to users to complain.
> 
> He was talking about WBINVD. But it made me think about how we
> use the split lock detection feature in Linux.
> 
> Existing code has three options for applications:
> 1) Don't enable split lock detection (allow arbitrary split locks)
> 2) Warn once when a process uses split lock, but let the process
>    keep running with split lock detection disabled
> 3) Kill process that use split locks

I'm not sure what split locks are, and if you want applications to
stop doing that maybe documentation would help.

Anyway, you can't really introduce regressions to userspace to "get
stuff fixed" in applications.
								Pavel
-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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