linux-kernel - Re: [PATCH] xen: core dom0 support

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Date:	Sun, 01 Mar 2009 16:08:39 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Xen-devel <xen-devel@...ts.xensource.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xen: core dom0 support

H. Peter Anvin wrote:
> In this particular case, this is actually false.  "No PAT" in the 
> processor is *not* the same thing as "no cacheability controls in the 
> page tables".  Every processor since the 386 has had UC, WT, and WB 
> controls in the page tables; PAT only added the ability to do WC (and 
> WP, which we don't use).  Since the number of processors which can do 
> WC at all but don't have PAT is a small set of increasingly obsolete 
> processors, we may very well choose to simply ignore the WC 
> capabilities of these particular processors. 

I'm not quite sure what you're referring to with "this is actually 
false".  Certainly we support cachability control in ptes under Xen.  We 
just don't support full PAT because Xen uses PAT for itself.

    J
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