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

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Message-ID: <4CAA52EF.3030302@zytor.com>
Date:	Mon, 04 Oct 2010 15:19:27 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Hugh Dickins <hughd@...gle.com>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>, 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

On 10/04/2010 03:17 PM, Hugh Dickins wrote:
> On Mon, Oct 4, 2010 at 2:21 PM, H. Peter Anvin <hpa@...or.com> wrote:
>> 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.
> 
> Another piece of the confusion I noticed a couple of days ago:
> X86_MINIMUM_CPU_FAMILY defaults to "6" if X86_32 &&
> X86_P6_NOP; whereas X86_P6_NOP depends on X86_64.
> 

Again, it's completely consistent -- if you keep in mind that
CONFIG_X86_P6_NOP depending on X86_64 is a policy decision; that policy
can theoretically be changed.  However, it really doesn't seem worth it
to ever contemplate at this point.

	-hpa
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