linux-kernel - Re: [PATCH] x86_64: clobber flags in clear

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Message-ID: <20180210211945.GA21424@pd.tnic>
Date:   Sat, 10 Feb 2018 22:19:46 +0100
From:   Borislav Petkov <bp@...e.de>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86_64: clobber flags in clear_page()

On Sat, Jan 13, 2018 at 09:50:48PM +0300, Alexey Dobriyan wrote:
> All clear_page() implementations use XOR which resets flags.
> 
> Judging by allyesconfig disassembly no code is affected.
> 
> Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
> ---
> 
>  arch/x86/include/asm/page_64.h |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/arch/x86/include/asm/page_64.h
> +++ b/arch/x86/include/asm/page_64.h
> @@ -47,7 +47,7 @@ static inline void clear_page(void *page)
>  			   clear_page_erms, X86_FEATURE_ERMS,
>  			   "=D" (page),
>  			   "0" (page)
> -			   : "memory", "rax", "rcx");
> +			   : "cc", "memory", "rax", "rcx");
>  }
>  
>  void copy_page(void *to, void *from);

Reviewed-by: Borislav Petkov <bp@...e.de>

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--