linux-kernel - Re: [PATCH] x86: pat cpu feature bit setting for known cpus

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Message-ID: <47E962AE.9040307@zytor.com>
Date:	Tue, 25 Mar 2008 13:38:06 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Venki Pallipadi <venkatesh.pallipadi@...el.com>,
	Yinghai Lu <yhlu.kernel@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	kernel list <linux-kernel@...r.kernel.org>,
	suresh.b.siddha@...el.com
Subject: Re: [PATCH] x86: pat cpu feature bit setting for known cpus

Ingo Molnar wrote:
> * Venki Pallipadi <venkatesh.pallipadi@...el.com> wrote:
> 
>>>>  OK, note previous question: what is the motivation for having 
>>>>  this as a whitelist (as opposed to a blacklist)?
>>> Venkatesh could tell?
>> Main reason for white-list at this point is not to be side-tracked by 
>> real or potential erratas on older CPUs. Focussing on getting the 
>> support for this feature on current and future CPUs. If older CPUs 
>> have survived all these days without this feature, they should be 
>> doing OK.
> 
> well, the upside would be that since most testing of Linux kernels is 
> done on _old_ hardware (people tend to risk their old hw first ;-), we'd 
> get faster convergence of the codebase, even though we have the risk of 
> erratas (known and unknown ones alike). Code that artificially limits 
> its utility is almost always slow to stabilize.
> 

Yes, using a whitelist of this type is wrong, IMO, and smells faintly of 
vendor-lockin.

	-hpa
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