linux-kernel - Re: [PATCH V6 04/11] compiler_types.h: Add __noinstr

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Date:   Mon, 24 Oct 2022 14:06:04 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Guo Ren <guoren@...nel.org>,
        Lai Jiangshan <laijs@...ux.alibaba.com>, arnd@...db.de,
        palmer@...osinc.com, tglx@...utronix.de, luto@...nel.org,
        conor.dooley@...rochip.com, heiko@...ech.de, jszhang@...nel.org,
        lazyparser@...il.com, falcon@...ylab.org, chenhuacai@...nel.org,
        apatel@...tanamicro.com, atishp@...shpatra.org, palmer@...belt.com,
        paul.walmsley@...ive.com, zouyipeng@...wei.com,
        bigeasy@...utronix.de, David.Laight@...lab.com,
        chenzhongjin@...wei.com, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        Borislav Petkov <bp@...en8.de>,
        Miguel Ojeda <ojeda@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH V6 04/11] compiler_types.h: Add __noinstr_section() for
 noinstr

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

> |  */
> | #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 :/).