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[Xen-devel] Re: [PATCH] xen: core dom0 support

To: "H. Peter Anvin" <hpa@xxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH] xen: core dom0 support
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Sun, 01 Mar 2009 16:08:39 -0800
Cc: the arch/x86 maintainers <x86@xxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Andi Kleen <andi@xxxxxxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>
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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.


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