linux-kernel - Re: [PATCH v3 4/9] x86: alternatives: macrofy locks for better inlining

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Date:   Mon, 11 Jun 2018 10:03:14 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Nadav Amit <namit@...are.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH v3 4/9] x86: alternatives: macrofy locks for better
 inlining

On Sun, Jun 10, 2018 at 07:19:06AM -0700, Nadav Amit wrote:
>  #ifdef CONFIG_SMP
> +.macro LOCK_PREFIX_HERE
>  	.pushsection .smp_locks,"a"
>  	.balign 4
> +	.long 671f - .		# offset
>  	.popsection
> +671:
> +.endm
> +
> +.macro LOCK_PREFIX insn:vararg
> +	LOCK_PREFIX_HERE
> +	lock \insn
> +.endm

Hurmph, the only reason we need to preserve that LOCK_PREFIX_HERE thing
is arch_cmpxchg64 in cmpxchg_32.h. Is there really no other way we can
write that one?

I suppose the problem with using LOCK_PREFIX inside the alternative is
that the .smp_locks fixup address gets computed wrong (inside the
alternative_text section instead of in the regular text)?

Oh well..