linux-kernel - Re: [PATCH -tip v2] x86/percpu: Introduce const-qualified const_pcpu

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Message-ID: <ZTPniJs9/ep11F2I@gmail.com>
Date:   Sat, 21 Oct 2023 17:00:24 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Uros Bizjak <ubizjak@...il.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Nadav Amit <namit@...are.com>
Subject: Re: [PATCH -tip v2] x86/percpu: Introduce const-qualified
 const_pcpu_hot


* Uros Bizjak <ubizjak@...il.com> wrote:

>  arch/x86/include/asm/current.h   | 7 +++++++
>  arch/x86/include/asm/percpu.h    | 6 +++---
>  arch/x86/include/asm/processor.h | 3 +++
>  arch/x86/kernel/cpu/common.c     | 1 +
>  arch/x86/kernel/vmlinux.lds.S    | 1 +
>  include/linux/compiler.h         | 2 +-
>  6 files changed, 16 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/include/asm/current.h b/arch/x86/include/asm/current.h
> index a1168e7b69e5..0538d2436673 100644
> --- a/arch/x86/include/asm/current.h
> +++ b/arch/x86/include/asm/current.h
> @@ -36,8 +36,15 @@ static_assert(sizeof(struct pcpu_hot) == 64);
>  
>  DECLARE_PER_CPU_ALIGNED(struct pcpu_hot, pcpu_hot);
>  
> +/* const-qualified alias to pcpu_hot, aliased by linker. */
> +DECLARE_PER_CPU_ALIGNED(const struct pcpu_hot __percpu_seg_override,
> +			const_pcpu_hot);

The aliasing makes me a bit nervous. Could we at least prefix it a bit more 
prominently, like const__pcpu_hot? That way it's immediately obvious at all 
usage sites that it's "special".

Thanks,

	Ingo