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

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Date:   Mon, 9 Oct 2023 13:51:55 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Uros Bizjak <ubizjak@...il.com>
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


* 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., while this OK for testing, this is too heavy handed for release 
purposes, so please only disable the KASAN instrumentation for the affected 
percpu accessors.

See the various __no_sanitize* attributes available.

I'd even suggest introducing a new attribute variant, specific to x86, 
prefixed with __no_sanitize_x86_seg or so, which would allow the eventual 
KASAN-instrumentation of the percpu accessors once the underlying GCC bug 
is fixed.

Thanks,

	Ingo