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Subject: Re: [PATCH] x86, cpu: X86_FEATURE_NOPL should be disabled on 32-bit only
From: "H. Peter Anvin" <hpa@zytor.com>
Date: Sun, 03 Oct 2010 15:22:13 -0700
To: Borislav Petkov <bp@alien8.de>
CC: Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
        lkml <linux-kernel@vger.kernel.org>
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Sort of... only if the input is a constant.

"Borislav Petkov" <bp@alien8.de> wrote:

>From: "H. Peter Anvin" <hpa@zytor.com>
>Date: Sun, Oct 03, 2010 at 11:19:18AM -0700
>
>> I think we actually need to set it on 64 bits.
>
>Ok, correct me if I'm wrong but I think it is already "indirectly" set
>on 64-bits through REQUIRED_MASK3:
>
>#define REQUIRED_MASK3  (NEED_NOPL)
>
>which is defined as
>
>#define NEED_NOPL      (1<<(X86_FEATURE_NOPL & 31))
>
>when either CONFIG_X86_P6_NOP or CONFIG_X86_64 are selected.
>
>and cpu_has() does
>
>#define cpu_has(c, bit)                                                 \
>        (__builtin_constant_p(bit) &&                                   \
>	...
>           (((bit)>>5)==3 && (1UL<<((bit)&31) & REQUIRED_MASK3)) ||     \
>	...
>	? 1 : test_cpu_cap(c, bit))
>
>which returns 1 when testing for X86_FEATURE_NOPL, no?
>
>-- 
>Regards/Gruss,
>    Boris.

-- 
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