linux-kernel - Re: [PATCH] x86 : omit duplicate processing at pte

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Date:	Sat, 15 Aug 2009 00:10:35 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	ohyama_sec@...el-networks.com
CC:	linux-kernel@...r.kernel.org,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [PATCH] x86 : omit duplicate processing at pte_pgprot()

On 08/09/09 08:43, ohyama_sec@...el-networks.com wrote:
> I suggest following PATCH that omit duplicate processing of mask.
>
> pte_pgprot() macro [arch/x86/include/asm/pgtable.h] call pte_flags() [arch/x86/include/asm/pgtable_types.h] that return value is masked by PTE_FLAGS_MASK in pte_flags() function, and this macro also masks the returned value by PTE_FLAGS_MASK.
>   

It probably won't make any difference in practice, because gcc will do a
common subexpression elimination for the "& PTE_FLAGS_MASK" between the
inline function and its caller.  But it does tidy things up a bit.

> I guess that we don't have to do the mask processing at pte_pgprot() macro because it has already been masked at pte_flags().
> So, how about the following PATCH ?
>
> 	<Hiroyasu OHYAMA>
>   

Please add a proper Signed-off-by: line.

Acked-by: Jeremy Fitzhardinge <jeremy@...p.org>

    J
> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
> index 3cc06e3..a0b454c 100644
> --- a/arch/x86/include/asm/pgtable.h
> +++ b/arch/x86/include/asm/pgtable.h
> @@ -265,7 +265,7 @@ static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
>         return __pgprot(preservebits | addbits);
>          }
>
>          -#define pte_pgprot(x) __pgprot(pte_flags(x) & PTE_FLAGS_MASK)
>          +#define pte_pgprot(x) __pgprot(pte_flags(x))
>
>           #define canon_pgprot(p) __pgprot(massage_pgprot(p))
> --
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>   

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