linux-kernel - Re: NOPL on 32-bit

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Message-ID: <4CA89681.8000202@zytor.com>
Date:	Sun, 03 Oct 2010 07:43:13 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: NOPL on 32-bit

On 10/03/2010 02:37 AM, Borislav Petkov wrote:
> Hi,
> 
> it looks like we currently clear X86_FEATURE_NOPL in detect_nopl()
> unconditionally and not only on 32-bit, as it should be according to
> ba0593bf553c450a03dbc5f8c1f0ff58b778a0c8.
> 
> I'm thinking maybe something like the following might be in order
> 
> --
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index caa967d..9a2cfeb 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -713,7 +713,9 @@ void __init early_cpu_init(void)
>   */
>  static void __cpuinit detect_nopl(struct cpuinfo_x86 *c)
>  {
> +#ifdef CONFIG_X86_32
>  	clear_cpu_cap(c, X86_FEATURE_NOPL);
> +#endif
>  }
>  
>  static void __cpuinit generic_identify(struct cpuinfo_x86 *c)
> --
> 

Yes, that's a bug.  It should be disabled only on 32 bits.

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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