linux-kernel - Re: [tip:x86/pat] x86: Relegate CONFIG_PAT and CONFIG

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Date:	Mon, 12 Oct 2009 19:56:26 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>, mingo@...hat.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	arjan@...radead.org, hmh@....eng.br, rdreier@...co.com,
	tglx@...utronix.de, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/pat] x86: Relegate CONFIG_PAT and CONFIG_MTRR
	configurability to EMBEDDED


* Arjan van de Ven <arjan@...ux.intel.com> wrote:

> H. Peter Anvin wrote:
>> On 10/12/2009 04:10 AM, tip-bot for Arjan van de Ven wrote:
>>> Commit-ID:  c03cb3149daed3e411657e3212d05ae27cf1a874
>>> Gitweb:     http://git.kernel.org/tip/c03cb3149daed3e411657e3212d05ae27cf1a874
>>> Author:     Arjan van de Ven <arjan@...radead.org>
>>> AuthorDate: Sun, 11 Oct 2009 10:33:02 -0700
>>> Committer:  Ingo Molnar <mingo@...e.hu>
>>> CommitDate: Mon, 12 Oct 2009 13:06:57 +0200
>>>
>>> x86: Relegate CONFIG_PAT and CONFIG_MTRR configurability to EMBEDDED
>>>
>>> MTRR and PAT support (which got added to CPUs over 10 years ago)
>>> are no longer really optional in that more and more things are
>>> depending on PAT just working, including various drivers and newer
>>> versions of X.  (to not even speak of MTRR)
>>>
>>> Having this as a regular config option just no longer makes sense.
>>>
>>> This patch relegates CONFIG_X86_PAT to the EMBEDDED category so
>>> ultra-embedded can still disable it if they really need to.
>>>
>>
>> Should we combine this with removing the whitelist (which is largely 
>> vestigial at this point) and replace it with a blacklist (possibly 
>> empty)?  I still haven't seen any evidence that there are any CPUs 
>> which have problems, and PAT support go back all the way to Pentium 
>> III -- and page table attributes can be used all the way back to 386, 
>> it just excludes the WC type.
>
> I would be in favor of that; other operating systems have been using 
> pat everywhere since the pII days anyway.

Fine to me too. We only made it a whitelist to reduce the degrees of 
freedom early in the implementation - it stuck around needlessly long.

	Ingo
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