From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754908AbZF3A0x (ORCPT ); Mon, 29 Jun 2009 20:26:53 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753382AbZF3A0p (ORCPT ); Mon, 29 Jun 2009 20:26:45 -0400 Received: from terminus.zytor.com ([198.137.202.10]:41218 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753039AbZF3A0o (ORCPT ); Mon, 29 Jun 2009 20:26:44 -0400 Message-ID: <4A495ABC.1090306@zytor.com> Date: Mon, 29 Jun 2009 17:22:20 -0700 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.14 (X11/20080501) MIME-Version: 1.0 To: Yinghai Lu CC: Linus Torvalds , Ingo Molnar , Mikael Pettersson , Matthew Wilcox , Grant Grundler , linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org Subject: Re: [BUG 2.6.31-rc1] HIGHMEM64G causes hang in PCI init on 32-bit x86 References: <200906261559.n5QFxJH8027336@pilspetsen.it.uu.se> <19013.29264.623540.275538@pilspetsen.it.uu.se> <4A45A5C1.5080701@zytor.com> <19013.59956.144640.331854@pilspetsen.it.uu.se> <20090629022911.GC20297@lackof.org> <4A484A8A.9020704@zytor.com> <19016.41349.636663.515540@pilspetsen.it.uu.se> <20090629112155.GJ5480@parisc-linux.org> <19016.44061.600652.676183@pilspetsen.it.uu.se> <4A490804.3040609@zytor.com> <4A494478.7020304@kernel.org> In-Reply-To: <4A494478.7020304@kernel.org> 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 Yinghai Lu wrote: >>> >> OK. This is starting to make sense. I suspect this is a similar issue >> as 3b0fde0fac19c180317eb0601b3504083f4b9bf5 addresses, which is that the >> e820 code assumes -- and I don't see any exception to that in >> 45fbe3ee01b8e463b28c2751b5dcc0cbdc142d90 -- that iomem_resource covers >> the entire 64-bit address space that e820 knows. I wonder what happens >> with "interestingly shaped" memory above 4 GB if resource_size_t is 32 >> bits with that code. >> >> In terms of address space assignment, an alternate implementation of the >> address space cap is to mark it reserved; that would unfortunately >> result in an ugly turd at the end of /proc/iomem, but that can be >> addressed if need be, too. > > always enable 64bit resource for 32bit too? > That would address the problem if combined with the "alternative implementation" that I described below, but I'm not sure how well it would go over, especially since the 32-bit x86 world is increasingly getting concentrated on the very-resource-starved end of the computing spectrum. The bottom-line problem is the same: e820, and the e820 allocator, can describe address space that lies outside our real range of possible address space. What to do with that is easy -- it should simply be ignored -- but it does lead to oddball sequencing issues. In that sense, reserving a chunk of address space at the end is cleaner, but that doesn't address the issue of what happens with a 32-bit resource_size_t. Unfortunately, my attempts at reproducing the problem locally has failed so far. -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf.