linux-kernel - Re: [PATCH] x86, cpu: Fix X86_FEATURE

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Message-ID: <20101004214838.GA26084@liondog.tnic>
Date:	Mon, 4 Oct 2010 23:48:38 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86, cpu: Fix X86_FEATURE_NOPL

From: "H. Peter Anvin" <hpa@...or.com>
Date: Mon, Oct 04, 2010 at 02:21:33PM -0700

> On 10/04/2010 02:12 PM, Linus Torvalds wrote:
> > On Mon, Oct 4, 2010 at 2:02 PM, H. Peter Anvin <hpa@...or.com> wrote:
> >>
> >> Actually, cpu_has() depends on:
> >> #if defined(CONFIG_X86_P6_NOP) || defined(CONFIG_X86_64)
> > 
> > Ahh. Right you are. The place that depends on just P6_NOP is the
> > default NOP choice logic in <asm/nops.h>
> > 
> > But the end result ends up being the same: can we please clean this
> > all up so that it isn't so confusing? Rather than add to the
> > confusion?
> > 
> 
> Agreed that this should be cleaned up.  However, in the meantime I'd
> like to keep Borislav's patch in the tree since it makes the code
> technically correct at least.

I think the cleanup should be easy: on 64-bit unconditionally return
p6_nops in find_nop_table() since every 64-bit processor should support
them and on 32-bit never return p6_nops since X86_FEATURE_NOPL is not
set there and fall back to intel_nops on non-AMD. Which means we can get
rid of X86_FEATURE_NOPL altogether. Too radical?

Hmmm...

-- 
Regards/Gruss,
    Boris.
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