linux-kernel - Re: [PATCH 2/3] x86/cpu: Elide KCSAN for cpu

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Message-ID: <Ym/GiZUb6Vqg+hy/@elver.google.com>
Date:   Mon, 2 May 2022 13:54:49 +0200
From:   Marco Elver <elver@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, jpoimboe@...hat.com, linux-kernel@...r.kernel.org,
        jbaron@...mai.com, rostedt@...dmis.org, ardb@...nel.org,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH 2/3] x86/cpu: Elide KCSAN for cpu_has() and friends

On Mon, May 02, 2022 at 01:07PM +0200, Peter Zijlstra wrote:
> vmlinux.o: warning: objtool: enter_from_user_mode+0x24: call to __kcsan_check_access() leaves .noinstr.text section
> vmlinux.o: warning: objtool: syscall_enter_from_user_mode+0x28: call to __kcsan_check_access() leaves .noinstr.text section
> vmlinux.o: warning: objtool: syscall_enter_from_user_mode_prepare+0x24: call to __kcsan_check_access() leaves .noinstr.text section
> vmlinux.o: warning: objtool: irqentry_enter_from_user_mode+0x24: call to __kcsan_check_access() leaves .noinstr.text section
> 
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Reviewed-by: Marco Elver <elver@...gle.com>

And should fix the same issue for other sanitizers that get instrumented
test_bit() via asm-generic/bitops/instrumented-*.h, not just KCSAN.

> ---
>  arch/x86/include/asm/cpufeature.h |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/arch/x86/include/asm/cpufeature.h
> +++ b/arch/x86/include/asm/cpufeature.h
> @@ -51,7 +51,7 @@ extern const char * const x86_power_flag
>  extern const char * const x86_bug_flags[NBUGINTS*32];
>  
>  #define test_cpu_cap(c, bit)						\
> -	 test_bit(bit, (unsigned long *)((c)->x86_capability))
> +	 arch_test_bit(bit, (unsigned long *)((c)->x86_capability))
>  
>  /*
>   * There are 32 bits/features in each mask word.  The high bits
> 
>