Re: [PATCH V6 04/11] compiler_types.h: Add __noinstr_section() for noinstr

From: Mark Rutland <mark.rutland@arm.com>
To: Guo Ren <guoren@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Lai Jiangshan <laijs@linux.alibaba.com>,
	arnd@arndb.de, palmer@rivosinc.com, tglx@linutronix.de,
	luto@kernel.org, conor.dooley@microchip.com, heiko@sntech.de,
	jszhang@kernel.org, lazyparser@gmail.com, falcon@tinylab.org,
	chenhuacai@kernel.org, apatel@ventanamicro.com,
	atishp@atishpatra.org, palmer@dabbelt.com,
	paul.walmsley@sifive.com, zouyipeng@huawei.com,
	bigeasy@linutronix.de, David.Laight@aculab.com,
	chenzhongjin@huawei.com, linux-arch@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
	Borislav Petkov <bp@alien8.de>, Miguel Ojeda <ojeda@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Nick Desaulniers <ndesaulniers@google.com>
Subject: Re: [PATCH V6 04/11] compiler_types.h: Add __noinstr_section() for noinstr
Date: Tue, 25 Oct 2022 10:47:25 +0100	[thread overview]
Message-ID: <Y1ewrRpHBwg2wJnb@FVFF77S0Q05N> (raw)
In-Reply-To: <CAJF2gTQvmSuOP_QQ8RGfq2soLrv9XD3g=8v9pE+U0y+pzqMY4A@mail.gmail.com>

On Tue, Oct 25, 2022 at 10:51:02AM +0800, Guo Ren wrote:
> On Mon, Oct 24, 2022 at 8:14 PM Mark Rutland <mark.rutland@arm.com> wrote:
> >
> > On Mon, Oct 24, 2022 at 02:06:04PM +0200, Peter Zijlstra wrote:
> > > On Mon, Oct 24, 2022 at 12:56:03PM +0100, Mark Rutland wrote:
> > >
> > > > How about we split this like:
> > > >
> > > > | /*
> > > > |  * Prevent the compiler from instrumenting this code in any way
> > > > |  * This does not prevent instrumentation via KPROBES, which must be
> > > > |  * prevented through other means if necessary.
> > >
> > > Perhaps point to NOINSTR_TEXT in vmlinux.lds.h
> >
> > Makes sense, will do.
> Do I need to update the comment with NOINSTR_TEXT? eg:
> 
>  * Prevent the compiler from instrumenting this code in any way
>  * This does not prevent instrumentation via KPROBES, which must be
>  * prevented through other means if necessary. See NOINSTR_TEXT
>  * in vmlinux.lds.h.

I think given Peter's reply we can leave the patch as-is for now, and we can
leave commentary or other changes to a later follow up. I'm happy to propose
patches for that once the existing bits are merged.

Sorry for confusing matters!

> > > > |  */
> > > > | #define __no_compiler_instrument                          \
> > > > |   noinline notrace noinline notrace __no_kcsan            \
> > > > |   __no_sanitize_address __no_sanitize_coverage
> > > > |
> > > > | /*
> > > > |  * Section for code which can't be instrumented at all.
> > > > |  * Any code in this section cannot be instrumented with KPROBES.
> > > > |  */
> > > > | #define noinstr __no_compiler_instrument section(".noinstr.text")
> > > >
> > > > ... then we don't need __noinstr_section(), and IMO the split is
> > > > clearer.
> > >
> > > Yeah, perhaps, no strong feelings. Note I have this in the sched-idle
> > > series as well (which I still need to rebase and repost :/).
> >
> > Ah; I'll sit on this for now then, and once that's all in I can send a
> > cleanup/rework patch. Sorry for the noise!
> We still keep __noinstr_section(), right?

Yes -- for now this patch can stay as-is, and __noinstr_section() will remain.

Thanks,
Mark.