linux-kernel - Re: [PATCH 12/24] x86-64: remove PGE from must-have feature list

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Message-ID: <49BD70B3.3030703@zytor.com>
Date:	Sun, 15 Mar 2009 14:18:43 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Xen-devel <xen-devel@...ts.xensource.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: Re: [PATCH 12/24] x86-64: remove PGE from must-have feature list

Jeremy Fitzhardinge wrote:
> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
> 
> PGE may not be available when running paravirtualized, so test the cpuid
> bit before using it.
> 
> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
> ---
>  arch/x86/include/asm/required-features.h |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/include/asm/required-features.h b/arch/x86/include/asm/required-features.h
> index d5cd6c5..a4737dd 100644
> --- a/arch/x86/include/asm/required-features.h
> +++ b/arch/x86/include/asm/required-features.h
> @@ -50,7 +50,7 @@
>  #ifdef CONFIG_X86_64
>  #define NEED_PSE	0
>  #define NEED_MSR	(1<<(X86_FEATURE_MSR & 31))
> -#define NEED_PGE	(1<<(X86_FEATURE_PGE & 31))
> +#define NEED_PGE	0
>  #define NEED_FXSR	(1<<(X86_FEATURE_FXSR & 31))
>  #define NEED_XMM	(1<<(X86_FEATURE_XMM & 31))
>  #define NEED_XMM2	(1<<(X86_FEATURE_XMM2 & 31))

This should be conditionalized on CONFIG_PARAVIRT, since doing this
removes real-hardware optimimizations.

	-hpa

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

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