From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758731AbZCAX4D (ORCPT ); Sun, 1 Mar 2009 18:56:03 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757327AbZCAXzo (ORCPT ); Sun, 1 Mar 2009 18:55:44 -0500 Received: from terminus.zytor.com ([198.137.202.10]:36245 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757273AbZCAXzn (ORCPT ); Sun, 1 Mar 2009 18:55:43 -0500 Message-ID: <49AB1FB8.607@zytor.com> Date: Sun, 01 Mar 2009 15:52:24 -0800 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.19 (X11/20090105) MIME-Version: 1.0 To: Jeremy Fitzhardinge CC: Andi Kleen , Andrew Morton , Xen-devel , the arch/x86 maintainers , Linux Kernel Mailing List Subject: Re: [PATCH] xen: core dom0 support References: <1235786365-17744-1-git-send-email-jeremy@goop.org> <20090227212812.26d02f34.akpm@linux-foundation.org> <49A8DF28.4050301@goop.org> <87eixi35ew.fsf@basil.nowhere.org> <49AB1B75.2060200@goop.org> In-Reply-To: <49AB1B75.2060200@goop.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Jeremy Fitzhardinge wrote: > > Unless we're planning on dropping support for processes with no or > broken PAT support, we're always going to have to deal with the non-PAT > case. Xen just falls into the "processor with no PAT" case. And > if/when we work out how to paravirtualize PAT, it will no longer be in > that case. > 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. -hpa