From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759011Ab2I2DQw (ORCPT ); Fri, 28 Sep 2012 23:16:52 -0400 Received: from terminus.zytor.com ([198.137.202.10]:46642 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758788Ab2I2DQt (ORCPT ); Fri, 28 Sep 2012 23:16:49 -0400 Message-ID: <5066680E.3090907@zytor.com> Date: Fri, 28 Sep 2012 20:16:30 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120605 Thunderbird/13.0 MIME-Version: 1.0 To: Peter Hurley CC: "zhenzhong.duan@oracle.com" , Thomas Gleixner , Ingo Molnar , "x86@kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [RFC] x86: mtrr: Constrain WB MTRR to max phys mem prior to cleanup References: <1347039854.6288.8.camel@thor> <504A3FA9.1050502@zytor.com> <504D6490.2060606@oracle.com> <1348853876.2229.22.camel@thor> In-Reply-To: <1348853876.2229.22.camel@thor> X-Enigmail-Version: 1.4.3 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/28/2012 10:37 AM, Peter Hurley wrote: > > An interesting side note: more recent revisions of this BIOS (rev. A11) > report one less variable MTRR (so, IA32_MTRRCAP is writable?) > >>> However, the right way to fix that is to use the PAT interfaces, which >>> doesn't have this drawback -- then MTRR cleanup becomes entirely >>> superfluous and the problem goes away. >> Do you mean disable MTRR totally here? > > Well, since PAT entries marked WC override all MTRR settings, whatever > the BIOS set the variable MTRRs to becomes irrelevant, so not disabled > but rather ignored. > The whole point is that the display stuff should not use MTRR, but rather use PAT to provide WC. Then we don't need to "clean up" the BIOS-set MTRRs. -hpa