linux-kernel - Re: [RFC PATCH 00/12] PAT 64b: PAT support for X86

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Message-ID: <alpine.DEB.0.82.0712140023550.27550@skynet.skynet.ie>
Date:	Fri, 14 Dec 2007 00:28:25 +0000 (GMT)
From:	Dave Airlie <airlied@...net.ie>
To:	venkatesh.pallipadi@...el.com
cc:	ak@....de, ebiederm@...ssion.com, rdreier@...co.com,
	torvalds@...ux-foundation.org, gregkh@...e.de, davej@...hat.com,
	mingo@...e.hu, tglx@...utronix.de, hpa@...or.com,
	akpm@...ux-foundation.org, arjan@...radead.org,
	jesse.barnes@...el.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 00/12] PAT 64b: PAT support for X86_64


> Yes. It is that wonderful time of the year again.
> No, no. We are not talking about holiday season or new year here.
> 
> We are talking about one another rehash of "why we do not support PAT in x86"
> question and series of patches that implement some PAT support before going
> into hibernation again. Only difference is that we hope to take this little
> further this time and may be really get this support into
> upstream kernel soon.

Woot, PAT support: this time we mean it!!

I'll just give one comment after a reading your todo..

> * Do we need to allow RAM pages to be mapped as WC? If not, then
>   we don't need to follow the TLB flush mechanism (make pte not present,
>   flush, and set pte with new mapping) mentioned in section 10.12.4 of SDM
>   Vol3a.

Yes, the main use for GPUs is to have RAM pages mapped WC, and placed into 
a GART on the GPU side, currently for Intel IGD we are okay as the CPU can 
access the GPU GART aperture, but other chips exist where this isn't 
possible, I think poulsbo and possible some of the AMD IGPs..

Dave.
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