linux-kernel - Re: [PATCH] x86: introduce a new Linux defined feature flag for PAT support

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Message-ID: <48232F86.7050308@zytor.com>
Date:	Thu, 08 May 2008 09:51:18 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Andi Kleen <andi@...stfloor.org>,
	Rene Herman <rene.herman@...access.nl>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Adrian Bunk <bunk@...nel.org>,
	Yinghai Lu <yhlu.kernel@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	akpm@...ux-foundation.org, Pavel Machek <pavel@...e.cz>
Subject: Re: [PATCH] x86: introduce a new Linux defined feature flag for PAT
 support

Alan Cox wrote:
>> For old CPUs it is actually ok (after all they worked for years without
>> PAT), I just don't like it for new CPUs. It's a bad idea there and
>> in the x86 world it is a reasonable expectation that CPU features
>> generally work.
> 
> Agreed 100%. We should default to assuming newer processors work. That
> will be true in almost if not all cases anyway, and since it'll bite
> anyone at Intel/AMD/.. testing new CPU steppings when it is on by default
> any problem cases won't be leaving the labs.

Yes, capping the upper end is an actively bad thing, because it can 
actually *make* bugs appear (by artifically limiting testing by CPU houses.)

	-hpa

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