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

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Date: Wed, 10 Apr 2024 13:21:23 +0200
From: Uros Bizjak <ubizjak@...il.com>
To: Andrey Konovalov <andreyknvl@...il.com>
Cc: Ingo Molnar <mingo@...nel.org>, 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>, 
	Andrey Ryabinin <ryabinin.a.a@...il.com>, Alexander Potapenko <glider@...gle.com>, 
	Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com
Subject: Re: [PATCH 4/4] x86/percpu: Use C for percpu read/write accessors

On Wed, Apr 10, 2024 at 1:11 PM Andrey Konovalov <andreyknvl@...il.com> wrote:
>
> On Mon, Oct 9, 2023 at 4:35 PM Uros Bizjak <ubizjak@...il.com> wrote:
> >
> > 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
> >
> > This is now PR sanitizer/111736 [1], but perhaps KASAN people [CC'd]
> > also want to be notified about this problem.
> >
> > [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111736
>
> Filed a KASAN bug to track this:
> https://bugzilla.kernel.org/show_bug.cgi?id=218703

Please note the fix in -tip tree that reenables sanitizers for fixed compilers:

https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=x86/percpu&id=9ebe5500d4b25ee4cde04eec59a6764361a60709

Thanks,
Uros.