linux-kernel - Re: [PATCH 4/4] x86/percpu: Use C for percpu read/write accessors

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Message-ID: <CAFULd4Yf9u2qvDyynDX3vSNNH+qCkxrpJocaKQnyH89sJLqHuA@mail.gmail.com>
Date:   Mon, 9 Oct 2023 14:27:34 +0200
From:   Uros Bizjak <ubizjak@...il.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        Nadav Amit <namit@...are.com>, 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>,
        Borislav Petkov <bp@...en8.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH 4/4] x86/percpu: Use C for percpu read/write accessors

On Mon, Oct 9, 2023 at 1:41 PM Ingo Molnar <mingo@...nel.org> wrote:
>
>
> * Uros Bizjak <ubizjak@...il.com> wrote:
>
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index ecb256954351..1edf4a5b93ca 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -2393,7 +2393,7 @@ config CC_HAS_NAMED_AS
> >
> >  config USE_X86_SEG_SUPPORT
> >       def_bool y
> > -     depends on CC_HAS_NAMED_AS && SMP
> > +     depends on CC_HAS_NAMED_AS && SMP && !KASAN
> > +     depends on CC_HAS_NAMED_AS && SMP && !KASAN
>
> So I'd rather express this as a Kconfig quirk line, and explain each quirk.
>
> Something like:
>
>         depends on CC_HAS_NAMED_AS
>         depends on SMP
>         #
>         # -fsanitize=kernel-address (KASAN) is at the moment incompatible
>         # with named address spaces - see GCC bug #12345.
>         #
>         depends on !KASAN
>
> ... or so.
>
> BTW., please also document the reason why !SMP is excluded.

Eh, thanks for pointing it out, it is not needed at all, it works also
for !SMP. Will fix in a Kconfig patch.

Thanks,
Uros.