Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756147Ab1DRRhD (ORCPT ); Mon, 18 Apr 2011 13:37:03 -0400 Received: from 8bytes.org ([88.198.83.132]:51607 "EHLO 8bytes.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754726Ab1DRRg5 (ORCPT ); Mon, 18 Apr 2011 13:36:57 -0400 Date: Mon, 18 Apr 2011 19:36:55 +0200 From: Joerg Roedel To: "H. Peter Anvin" Cc: "Roedel, Joerg" , Ingo Molnar , Thomas Gleixner , "x86@kernel.org" , "linux-kernel@vger.kernel.org" , Yinghai Lu Subject: Re: [PATCH 1/4] x86, gart: Don't enforce GART aperture lower-bound by alignment Message-ID: <20110418173655.GA8155@8bytes.org> References: <1303134346-5805-1-git-send-email-joerg.roedel@amd.com> <1303134346-5805-2-git-send-email-joerg.roedel@amd.com> <4DAC4E7F.1010502@zytor.com> <20110418145653.GI2192@amd.com> <4DAC5E16.1020408@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4DAC5E16.1020408@zytor.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2047 Lines: 44 On Mon, Apr 18, 2011 at 08:51:50AM -0700, H. Peter Anvin wrote: > On 04/18/2011 07:56 AM, Roedel, Joerg wrote: > > On Mon, Apr 18, 2011 at 10:45:19AM -0400, H. Peter Anvin wrote: > >> On 04/18/2011 06:45 AM, Joerg Roedel wrote: > >>> This patch changes the allocation of the GART aperture to > >>> enforce only natural alignment instead of aligning it on > >>> 512MB. This big alignment was used to force the GART > >>> aperture to be over 512MB. This is enforced by using 512MB > >>> as the lower-bound address in the allocation range. > >>> > >>> Cc: Yinghai Lu > >>> Signed-off-by: Joerg Roedel > >> > >> Better implementation of the existing bounds, yes, but I think the > >> algorithm is still wrong. Specifically, 512 MiB seems to have been the > >> maximum address of the kernel at some point, but that is historic at > >> this point, at least on 64 bits. > > > > I am fine with a smaller lower-bound, but I am not sure what a better > > choice is. The comment about kexec seems to be valid. It shouldn't matter > > for kdump because in this case the memory is allocated independently and > > the kdump kernel will only use this part, but for other kexec uses it is > > a bit harder. Probably any number we choose as a lower bound is an > > arbitrary choice at some point. But I am open for > > suggestions/corrections to this. > > > > The right thing to do for in-place kexec it to turn it off, not rely on > any specific magic addresses. We have had this problem with a number of > drivers in the context of kexec. Ok, so changing the start-address to zero seems the best thing to do. This way the GART will working again on machines with less than 512MB of RAM (and a BIOS that does not initialize the GART as we want it). Regards, Joerg -- 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/