linux-kernel - Re: [RFC Patch] use MTRR for write combining if PAT is not available

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Message-ID: <20091019153134.GA18198@elte.hu>
Date:	Mon, 19 Oct 2009 17:31:34 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Thomas Schlichter <thomas.schlichter@....de>
Cc:	Jan Beulich <JBeulich@...ell.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	arjan@...ux.intel.com, dri-devel@...ts.sourceforge.net,
	hancockrwd@...il.com, hmh@....eng.br, hpa@...or.com,
	jbarnes@...tuousgeek.org, jeremy.fitzhardinge@...rix.com,
	linux-kernel@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de,
	thellstrom@...are.com, tj@...nel.org,
	venkatesh.pallipadi@...el.com, x86@...nel.org, yinghai@...nel.org
Subject: Re: [RFC Patch] use MTRR for write combining if PAT is not
	available


* Thomas Schlichter <thomas.schlichter@....de> wrote:

> I don't think this is a good idea, Robert Hancock wrote there may be 
> millions of such Laptops (Core Solo/Duo erratum AE7, Pentium M erratum 
> Y31) :
>
>   http://marc.info/?l=linux-kernel&m=125537136105246&w=2
> 
> > or Perhaps just try to add mtrr only for the pci mmap case like the 
> > 4th patch in this series..
> 
> I'd prefer this! ;-)

Hm, we could perhaps do that - but i think we should only do that on 
systems that have PAT disabled.

Which brings up the question of how to properly QA such a narrow segment 
of the market. Maybe disabling CONFIG_X86_PAT should enable that logic 
too.

	Ingo
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