linux-kernel - Re: [PATCH 15/15] x86/percpu: Remove !CONFIG_X86

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Message-ID: <CAFULd4agC7vH2hnLFrwYmu1GLztwgH6+LRzyWM-RuZQL009xrw@mail.gmail.com>
Date: Sun, 14 Dec 2025 10:38:47 +0100
From: Uros Bizjak <ubizjak@...il.com>
To: Ingo Molnar <mingo@...nel.org>
Cc: linux-kernel@...r.kernel.org, "Ahmed S . Darwish" <darwi@...utronix.de>, 
	Andrew Cooper <andrew.cooper3@...rix.com>, Ard Biesheuvel <ardb@...nel.org>, 
	Arnd Bergmann <arnd@...nel.org>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, "H . Peter Anvin" <hpa@...or.com>, 
	John Ogness <john.ogness@...utronix.de>, Linus Torvalds <torvalds@...ux-foundation.org>, 
	Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 15/15] x86/percpu: Remove !CONFIG_X86_CX8 methods

On Sun, Dec 14, 2025 at 9:48 AM Ingo Molnar <mingo@...nel.org> wrote:
>
> From: Uros Bizjak <ubizjak@...il.com>
>
> Adjust the constraints to the non-alternatives asm() statement.
>
> Signed-off-by: Uros Bizjak <ubizjak@...il.com>
> Signed-off-by: Ingo Molnar <mingo@...nel.org>
> Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: "Ahmed S . Darwish" <darwi@...utronix.de>
> Cc: Andrew Cooper <andrew.cooper3@...rix.com>
> Cc: Ard Biesheuvel <ardb@...nel.org>
> Cc: Arnd Bergmann <arnd@...nel.org>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: "H . Peter Anvin" <hpa@...or.com>
> Cc: John Ogness <john.ogness@...utronix.de>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Link: https://lore.kernel.org/r/15696bb3-126b-ef71-f838-80e1e1c1b0aa@gmail.com
> ---
>  arch/x86/include/asm/percpu.h | 25 ++++++++++---------------
>  1 file changed, 10 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
> index 725d0eff7acd..4c84ae0ea261 100644
> --- a/arch/x86/include/asm/percpu.h
> +++ b/arch/x86/include/asm/percpu.h
> @@ -335,13 +335,10 @@ do {                                                                      \
>         old__.var = _oval;                                              \
>         new__.var = _nval;                                              \
>                                                                         \
> -       asm_inline qual (                                               \
> -               ALTERNATIVE("call this_cpu_cmpxchg8b_emu",              \
> -                           "cmpxchg8b " __percpu_arg([var]), X86_FEATURE_CX8) \
> -               : ALT_OUTPUT_SP([var] "+m" (__my_cpu_var(_var)),        \
> -                               "+a" (old__.low), "+d" (old__.high))    \
> -               : "b" (new__.low), "c" (new__.high),                    \
> -                 "S" (&(_var))                                         \
> +       asm qual ("cmpxchg8b " __percpu_arg([var])                      \
> +               : "+m" (__my_cpu_var(_var)),                            \

The above line should read:

              : [var] "+m" (__my_cpu_var(_var)),

> +                 "+a" (old__.low), "+d" (old__.high)                   \
> +               : "b" (new__.low), "c" (new__.high)                     \
>                 : "memory");                                            \
>                                                                         \
>         old__.var;                                                      \
> @@ -364,14 +361,12 @@ do {                                                                      \
>         old__.var = *_oval;                                             \
>         new__.var = _nval;                                              \
>                                                                         \
> -       asm_inline qual (                                               \
> -               ALTERNATIVE("call this_cpu_cmpxchg8b_emu",              \
> -                           "cmpxchg8b " __percpu_arg([var]), X86_FEATURE_CX8) \
> -               : ALT_OUTPUT_SP("=@ccz" (success),                      \
> -                               [var] "+m" (__my_cpu_var(_var)),        \
> -                               "+a" (old__.low), "+d" (old__.high))    \
> -               : "b" (new__.low), "c" (new__.high),                    \
> -                 "S" (&(_var))                                         \
> +       asm qual ("cmpxchg8b " __percpu_arg([var])                      \
> +               CC_SET(z)                                               \
> +               : CC_OUT(z) (success),                                  \

CC_SET() and CC_OUT() macros have been removed in the meantime [1], so
the last two lines should be changed to:

    : "=@ccz" (success),

[1] https://lore.kernel.org/lkml/20250907183420.48569-1-ubizjak@gmail.com/

Uros.