Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759155AbXFDSWS (ORCPT ); Mon, 4 Jun 2007 14:22:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757416AbXFDSWI (ORCPT ); Mon, 4 Jun 2007 14:22:08 -0400 Received: from lucidpixels.com ([75.144.35.66]:59673 "EHLO lucidpixels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756327AbXFDSWH (ORCPT ); Mon, 4 Jun 2007 14:22:07 -0400 Date: Mon, 4 Jun 2007 14:22:05 -0400 (EDT) From: Justin Piszcz X-X-Sender: jpiszcz@p34.internal.lan To: "Eric W. Biederman" cc: Jesse Barnes , Andi Kleen , 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? In-Reply-To: Message-ID: References: <200706011407.51779.jbarnes@virtuousgeek.org> <20070601211943.GO7217@one.firstfloor.org> <200706011441.57149.jbarnes@virtuousgeek.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2643 Lines: 61 On Mon, 4 Jun 2007, Eric W. Biederman wrote: > 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 > According to Intel it is not a BIOS bug but rather the media controller hub (MCH) uses memory for various purposes, outlined in their doc: >From their response, it sounds like the kernel needs to setup the memory properly to deal with the MCH found in the 965 motherboards? >From their e-mail: Note before continuing: Debian* Linux Operating System is not an officially, validated, tested Operating System for the Intel(R) Desktop Board DG965WH (see http://downloadcenter.intel.com/Product_Filter.aspx?ProductID=2375); moreover, we do confirm that "on a system that has 8 GB of system memory installed, it is not possible to use all of the installed memory due to system address space being allocated for other system critical functions." [qtd. on page 43 of the Technical Product Specification (see http://download.intel.com/design/motherbd/wh/D5600801US.pdf)]. Thus, the following suggestions are provided AS IS; we cannot guarantee the problem would be fixed afterwards: Therefore, they are NOT going to fix their BIOS-- and I have already received an e-mail from one or two people who are experiencing this problem, I presume it will only get worse. Justin. - 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/