From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755185AbYHOKYh (ORCPT ); Fri, 15 Aug 2008 06:24:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752331AbYHOKY3 (ORCPT ); Fri, 15 Aug 2008 06:24:29 -0400 Received: from vpn.id2.novell.com ([195.33.99.129]:1945 "EHLO vpn.id2.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751995AbYHOKY2 convert rfc822-to-8bit (ORCPT ); Fri, 15 Aug 2008 06:24:28 -0400 Message-Id: <48A575B3.76E4.0078.0@novell.com> X-Mailer: Novell GroupWise Internet Agent 7.0.3 Date: Fri, 15 Aug 2008 11:25:23 +0100 From: "Jan Beulich" To: "Ingo Molnar" , "Venkatesh Pallipadi" , "Thomas Gleixner" , Cc: "Jeremy Fitzhardinge" , Subject: Why can't _PAGE_PROTNONE be _PAGE_ACCESSED? Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org With the overlaying of _PAGE_PSE and _PAGE_PAT there is a latent issue with the definition of _PAGE_PROTNONE: As soon as _PAGE_PAT gets actively used, it'll need to become part of _PAGE_CHG_MASK, and hence _PAGE_PROTNONE cannot use _PAGE_PSE anymore. One option certainly is to use one of the two remaining unused (available) bits, but it would seem to me that simply using _PAGE_ACCESSED here ought to work - but perhaps I'm overlooking some critical aspect? The background of this is that Xen's dom0 (and similarly DomU-s that have physical devices assigned) cannot change the setting in PAT_MSR, and hence has to live with being required to use _PAGE_PAT for establishing WC mappings. That'll be a requirement for Dom0 and pv pass-through support in the mainline tree (whenever that gets enabled) anyway, but I'll have to do it eagerly in our forward-ported Xen tree, which is why I'm trying to settle early on the route to take here. Thanks, Jan