linux-kernel - Re: This kernel requires the following features not present on the CPU... (on a VIA C7 CPU)

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Date:	Thu, 17 May 2007 15:19:14 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Simon Arlott <simon@...e.lp0.eu>
CC:	Claas Langbehn <claas@...tdir.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: This kernel requires the following features not present on the
 CPU... (on a VIA C7 CPU)

Simon Arlott wrote:
> On 17/05/07 21:15, H. Peter Anvin wrote:
>> Simon Arlott wrote:
>>> Is it automatic? I have CONFIG_X86_CMPXCHG=y without cx8 showing in
>>> cpuinfo, and it appears to work fine.
>>>
>>> Will your changes needlessly prevent the kernel running? Would I be
>>> right in thinking that the kernel is successfully using cmpxchg even
>>> though it's considered disabled? I realise people compile kernels for
>>> the wrong CPU but preventing them working when it's been chosen
>>> correctly seems wrong.
>>>
>>
>> CX8 isn't cmpxchg; it's cmpxchg8b.
> 
> Ok, but I have CONFIG_X86_CMPXCHG64=y too.
> 

OK then, then VIA just masks the CPUID bit as opposed to the
instruction.  Point still holds.

	-hpa
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