linux-kernel - Re: [PATCH 14/20] x86/barrier: Use alternative

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Message-ID: <Z9U_yvs8Cl0IEAQd@gmail.com>
Date: Sat, 15 Mar 2025 09:52:26 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Josh Poimboeuf <jpoimboe@...nel.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>,
	Uros Bizjak <ubizjak@...il.com>,
	Andrew Cooper <andrew.cooper3@...rix.com>
Subject: Re: [PATCH 14/20] x86/barrier: Use alternative_io() in 32-bit
 barrier functions


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Fri, 14 Mar 2025 at 11:42, Josh Poimboeuf <jpoimboe@...nel.org> wrote:
> >
> > +#define mb() alternative_io("lock addl $0,-4(%%esp)",                  \
> > +                           "mfence", X86_FEATURE_XMM2,                 \
> > +                           ARG(),                                      \
> > +                           ARG(),                                      \
> > +                           ARG("memory", "cc"))
> 
> So all of these patches look like good cleanups to me, but I do wonder
> if we should
> 
>  (a) not use some naming *quite* as generic as 'ARG()'
> 
>  (b) make the asms use ARG_OUT/ARG_IN/ARG_CLOBBER() to clarify
> 
> because that ARG(), ARG(), ARGC() pattern looks odd to me.
> 
> Maybe it's just me.

Not just you, and I think the ARG_ prefix still looks a bit too 
generic-C to me, it should be something more specific and unambiguously 
asm() related, like:

	ASM_ARGS_IN(),
	ASM_ARGS_OUT(),
	ASM_ARGS_CLOBBER(),

or maybe even:

	ASM_CONSTRAINT_IN(),
	ASM_CONSTRAINT_OUT(),
	ASM_CONSTRAINT_CLOBBER(),

Because these asm()-ish syntactic constructs look better in separate 
lines anyway, and it's not like we are at risk of running out of 
letters in the kernel anytime soon.

Thanks,

	Ingo