linux-kernel - Re: [PATCH v2 -tip] x86/percpu: Use C for arch_raw_cpu

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Date:   Wed, 18 Oct 2023 11:11:24 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Uros Bizjak <ubizjak@...il.com>
Cc:     Nadav Amit <namit@...are.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux Kernel Mailing List <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>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH v2 -tip] x86/percpu: Use C for arch_raw_cpu_ptr()

On Wed, 18 Oct 2023 at 10:23, Uros Bizjak <ubizjak@...il.com> wrote:
>
> In processor.h, we have:
>
> static __always_inline unsigned long current_top_of_stack(void)

Yeah, but that is never used multiple times afaik. I think it's purely
for things like

        WARN_ON_ONCE(!on_thread_stack());

in the entry code, for example.

So I guess it can use the same infrastructure, but I doubt it matters
in any practical way.

Grepping around for it, it looks like the 32-bit code has some stale commentary:

         * Reload esp0 and pcpu_hot.top_of_stack.  This changes
         * current_thread_info().

but that seems entirely bogus. We historically picked up
current_thread_info() from %esp, but that hasn't been true in ages,
afaik. Now it's all based on 'current'.

           Linus