From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932290AbXHHKOu (ORCPT ); Wed, 8 Aug 2007 06:14:50 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754017AbXHHKOo (ORCPT ); Wed, 8 Aug 2007 06:14:44 -0400 Received: from one.firstfloor.org ([213.235.205.2]:55119 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753835AbXHHKOn (ORCPT ); Wed, 8 Aug 2007 06:14:43 -0400 Date: Wed, 8 Aug 2007 12:14:41 +0200 From: Andi Kleen To: Loic Prylli Cc: Andi Kleen , =?iso-8859-1?Q?C=E9dric?= Augonnet , Linux Kernel Mailing List , Andrew Morton , brice@myri.com, cedric.augonnet@ens-lyon.org Subject: Re: PAT support for i386 and x86_64 Message-ID: <20070808101441.GA12861@one.firstfloor.org> References: <20070807083004.GB30085@one.firstfloor.org> <46B97E39.3020905@myri.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <46B97E39.3020905@myri.com> User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > I don't see why we have to worry about cache corruption in the case at > hand. Write-combining is needed to map io (typically pci-mem regions) > which are never mapped cachable anywhere, including in the linear map. If we WC them using PAT then there would be a UC<->WC conflict with the direct mapping and possibly others. That's already undefined and not allowed. After some very bad experiences in the past I'm not going to take chances on this. We really need to keep all possible mappings synchronized. -Andi