linux-kernel - Re: [PATCH 1/3] x86: fix access_ok() and valid_user_address() using wrong USER_PTR

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Message-ID: <20251106131030.GDaQyeRiAVoIh_23mg@fat_crate.local>
Date: Thu, 6 Nov 2025 14:10:30 +0100
From: Borislav Petkov <bp@...en8.de>
To: Mateusz Guzik <mjguzik@...il.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
	the arch/x86 maintainers <x86@...nel.org>, brauner@...nel.org,
	viro@...iv.linux.org.uk, jack@...e.cz, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, tglx@...utronix.de, pfalcato@...e.de
Subject: Re: [PATCH 1/3] x86: fix access_ok() and valid_user_address() using
 wrong USER_PTR_MAX in modules

On Thu, Nov 06, 2025 at 01:06:06PM +0100, Mateusz Guzik wrote:
> I don't know what are you trying to say here.
> 
> Are you protesting the notion that reducing cache footprint of the
> memory allocator is a good idea, or perhaps are you claiming these
> vars are too problematic to warrant the effort, or something else?

I'm saying all work which does not change the code in a trivial way should
have numbers to back it up. As in: "this change X shows this perf improvement
Y with the benchmark Z."

Because code uglification better have a fair justification.

Not just random "oh yeah, it would be better to have this." If the changes are
trivial, sure. But the runtime const thing was added for a very narrow case,
AFAIR, and it wasn't supposed to have a widespread use. And it ain't that
trivial, codewise.

IOW, no non-trivial changes which become a burden to maintainers without
a really good reason for them. This has been the guiding principle for
non-trivial perf optimizations in Linux. AFAIR at least.

But hey, what do I know...

-- 
Regards/Gruss,
    Boris.

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