From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754092Ab1JTVal (ORCPT ); Thu, 20 Oct 2011 17:30:41 -0400 Received: from terminus.zytor.com ([198.137.202.10]:33751 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752215Ab1JTVaa (ORCPT ); Thu, 20 Oct 2011 17:30:30 -0400 Message-ID: <4EA092DD.8020203@zytor.com> Date: Thu, 20 Oct 2011 14:30:05 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:7.0) Gecko/20110927 Thunderbird/7.0 MIME-Version: 1.0 To: Andi Kleen CC: Jacob Shin , Thomas Gleixner , Ingo Molnar , Yinghai Lu , Andreas Herrmann , x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/1] x86: Exclude E820_RESERVED regions and memory holes above 4 GB from direct mapping. References: <1319145326-13902-1-git-send-email-jacob.shin@amd.com> In-Reply-To: X-Enigmail-Version: 1.3.2 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/20/2011 02:28 PM, Andi Kleen wrote: > Jacob Shin writes: > >> On systems with very large memory (1 TB in our case), BIOS may report a >> reserved region or a hole in the E820 map, even above the 4 GB range. Exclude >> these from the direct mapping. > > This doesn't make much sense. Holes above 4GB are completely legal. > > If you need to workaround a specific broken BIOS you would need a quirk > only matching that system, with a suitable "BIOS is broken" message. > The problem is that apparently right now we map those unconditionally into the 1:1 map and mark them cacheable in PAT, which we *don't* for the < 4 GiB map. This thus makes the behavior match < 4 GiB, which is the correct behavior; this should be made clear in the patch description. -hpa