From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161001AbXDWRXr (ORCPT ); Mon, 23 Apr 2007 13:23:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1161095AbXDWRXq (ORCPT ); Mon, 23 Apr 2007 13:23:46 -0400 Received: from terminus.zytor.com ([192.83.249.54]:56055 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1161001AbXDWRXp (ORCPT ); Mon, 23 Apr 2007 13:23:45 -0400 Message-ID: <462CEB55.9070508@zytor.com> Date: Mon, 23 Apr 2007 10:22:29 -0700 From: "H. Peter Anvin" User-Agent: Thunderbird 1.5.0.10 (X11/20070302) MIME-Version: 1.0 To: Jeremy Fitzhardinge CC: "Eric W. Biederman" , Chuck Ebbert , Andi Kleen , Andrew Morton , virtualization@lists.osdl.org, lkml , Zachary Amsden , Chris Wright , Linus Torvalds Subject: Re: [PATCH 10/28] i386: map enough initial memory to create lowmem mappings References: <20070414204154.871250608@goop.org> <200704192250.52633.ak@suse.de> <4627D756.5020405@zytor.com> <200704192304.01053.ak@suse.de> <4627DB0C.2010804@zytor.com> <4627DDAD.4070805@redhat.com> <4627E099.209@goop.org> <462CE027.4030302@goop.org> <462CE1E0.9060007@zytor.com> <462CE69E.8040207@goop.org> In-Reply-To: <462CE69E.8040207@goop.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Jeremy Fitzhardinge wrote: > H. Peter Anvin wrote: >> Since we allocate the maximum possible memory statically, I fail to >> see how holes could make the situation any worse, or better. > > No, we map enough space to map 4G (~4 pages), but we don't actually map > 4G. If a hole happened to start within that 4 page mapping, then the > memory still wouldn't be available for allocation. > > I think this is a bit of a spurious argument though, since if it were > really a problem we'd have to worry about holes hitting the kernel image > too. As far as I can see, that's not considered to be a problem. > > I think the real point is that there's currently a subtle dependency > between head.S and bootmem allocation which happens between start_kernel > and pagetable_init. Your patch preventing over-mapping should make them > easier to smoke out as it currently stands, but eliminating the problem > by making alloc_bootmem create the mappings for itself does have > appeal. There would still be the dependency on head.S to map the kernel > itself and the bootmem allocator bitmap. > Agreed. However, saying that your patch shouldn't go into the mainline kernel until that has been fixed is spurious and wrong. It fixes a real problem with minimal risk. -hpa