From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932443AbXA1Hy0 (ORCPT ); Sun, 28 Jan 2007 02:54:26 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932436AbXA1Hy0 (ORCPT ); Sun, 28 Jan 2007 02:54:26 -0500 Received: from terminus.zytor.com ([192.83.249.54]:40835 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932443AbXA1HyZ (ORCPT ); Sun, 28 Jan 2007 02:54:25 -0500 Message-ID: <45BC56A0.1000906@zytor.com> Date: Sat, 27 Jan 2007 23:54:08 -0800 From: "H. Peter Anvin" User-Agent: Thunderbird 1.5.0.9 (X11/20061219) MIME-Version: 1.0 To: Mikael Pettersson CC: linux-kernel@vger.kernel.org, thomas@tungstengraphics.com Subject: Re: Support for i386 PATs References: <200701271059.l0RAxxP5018994@harpo.it.uu.se> In-Reply-To: <200701271059.l0RAxxP5018994@harpo.it.uu.se> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Mikael Pettersson wrote: > > 3) Many Intel processors, including at least most P6s and probably > also some P4s, have an erratum which effectively halves the number > of available PAT entries, forcing an OS to make the low 4 and upper > 4 PAT entries identical. > > I don't know if 4 PAT types suffice for the kinds of uses people > have in mind. But support for PAT would either have to restrict > itself to only 4 PAT types, or ensure that it is only enabled on > new enough processors where it actually works. > > You will need to read all available Intel errata sheets (spec updates) > to determine which processors are affected and which are OK. > There aren't really that many useful caching types, so it probably doesn't matter all that much. The types that matters most are WB, WC, and UC. The fourth one could be WT, or it could be UC- (however, UC- can *always* be emulated by simply having the kernel being aware of the MTRR settings.) -hpa