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Date: Wed, 07 May 2008 19:28:57 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Linus Torvalds <torvalds@linux-foundation.org>
CC: Rene Herman <rene.herman@keyaccess.nl>,
       Thomas Gleixner <tglx@linutronix.de>, Adrian Bunk <bunk@kernel.org>,
       Yinghai Lu <yhlu.kernel@gmail.com>, Ingo Molnar <mingo@elte.hu>,
       Linux Kernel <linux-kernel@vger.kernel.org>, akpm@linux-foundation.org,
       Pavel Machek <pavel@suse.cz>
Subject: Re: [PATCH] x86: introduce a new Linux defined feature flag for PAT
 support
References: <48210A71.1060409@keyaccess.nl> <86802c440805061939q39ff5500h3c9e229ecbc6b2e6@mail.gmail.com> <20080507124650.GD29935@cs181133002.pp.htv.fi> <alpine.LFD.1.10.0805072122270.3318@apollo.tec.linutronix.de> <48221AE3.6020602@keyaccess.nl> <482233F0.7040000@zytor.com> <48224318.8020209@keyaccess.nl> <48224361.5080102@zytor.com> <48224507.8010102@keyaccess.nl> <alpine.LFD.1.10.0805071716060.3024@woody.linux-foundation.org> <48224930.9030901@keyaccess.nl> <48225DEC.2030502@keyaccess.nl> <alpine.LFD.1.10.0805071857430.3024@woody.linux-foundation.org> <4822614B.6080706@zytor.com> <alpine.LFD.1.10.0805071923030.3024@woody.linux-foundation.org>
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Linus Torvalds wrote:
> 
>> *Certainly* I don't want anything like this crap:
>>
>>> -    if (cpu_has_pat)
>>> +    if (cpu_has_pat && cpu_has_pat_good)
> 
> This in fact is likely the best part of it.
> 
> Because that at least guarantees that we never say we have a good PAT when 
> the hardware doesn't even report it.
> 
> As it is, we seem to just blindly override hardware. It may be correct for 
> all the models we override, but still..
> 

Yah, this is not good.  We should mask out the bit, but never, ever, set 
it if it was clear to begin with (unless we have it on really, *really*, 
good authority.)

I'm embarrassed to have let that slink by.

	-hpa