Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759884AbXFDSOb (ORCPT ); Mon, 4 Jun 2007 14:14:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754415AbXFDSOY (ORCPT ); Mon, 4 Jun 2007 14:14:24 -0400 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:51450 "EHLO ebiederm.dsl.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755934AbXFDSOX (ORCPT ); Mon, 4 Jun 2007 14:14:23 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Jesse Barnes Cc: Andi Kleen , Justin Piszcz , linux-kernel@vger.kernel.org Subject: Re: Intel's response Linux/MTRR/8GB Memory Support / Why doesn't the kernel realize the BIOS has problems and re-map appropriately? References: <200706011407.51779.jbarnes@virtuousgeek.org> <20070601211943.GO7217@one.firstfloor.org> <200706011441.57149.jbarnes@virtuousgeek.org> Date: Mon, 04 Jun 2007 12:13:12 -0600 In-Reply-To: <200706011441.57149.jbarnes@virtuousgeek.org> (Jesse Barnes's message of "Fri, 1 Jun 2007 14:41:57 -0700") Message-ID: User-Agent: Gnus/5.110006 (No Gnus v0.6) Emacs/21.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1382 Lines: 30 Jesse Barnes writes: > On Friday, June 1, 2007 2:19:43 Andi Kleen wrote: >> And normally the MTRRs win, don't they (if I remember the table correctly) >> So if the MTRR says UC and PAT disagrees it might not actually help > > I just checked, yes the MTRRs win for UC types. But it sounds like the cases > we're talking about are actually situations where there's no MTRR coverage, > so the default type is used. The manual doesn't specifically call out how > memory using the default type interacts with PAT, but it may well be that it > stays uncached if the default type is uncached. Again that argues for fixing > the MTRR mapping problem in some way. Last I looked PAT can only demote not promote the type of a page, except for the specific exception of UC to WC. Normally the default type is UC so putting a pat type of WB won't help anything. I may have missed some subtle detail but I remember looking into this in some detail a while ago and coming to that conclusion. It is the BIOS's responsibility to mark all usable memory as WB, using the MTRRs. If it doesn't it is a BIOS bug. Eric - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/