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

From: Ingo Molnar <mingo@kernel.org>
To: Uros Bizjak <ubizjak@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	Andy Lutomirski <luto@kernel.org>, Nadav Amit <namit@vmware.com>,
	Brian Gerst <brgerst@gmail.com>,
	Denys Vlasenko <dvlasenk@redhat.com>,
	"H . Peter Anvin" <hpa@zytor.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Borislav Petkov <bp@alien8.de>,
	Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [PATCH 4/4] x86/percpu: Use C for percpu read/write accessors
Date: Mon, 9 Oct 2023 13:51:55 +0200	[thread overview]
Message-ID: <ZSPpW3zLTn7IohOJ@gmail.com> (raw)
In-Reply-To: <ZSPm6Z/lTK1ZlO8m@gmail.com>

* Ingo Molnar <mingo@kernel.org> wrote:

> 
> * Uros Bizjak <ubizjak@gmail.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