From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752278AbYL3G1k (ORCPT ); Tue, 30 Dec 2008 01:27:40 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751259AbYL3G1b (ORCPT ); Tue, 30 Dec 2008 01:27:31 -0500 Received: from out01.mta.xmission.com ([166.70.13.231]:57002 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751187AbYL3G1a (ORCPT ); Tue, 30 Dec 2008 01:27:30 -0500 From: ebiederm@xmission.com (Eric W. Biederman) To: Nick Piggin Cc: Andrew Morton , linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@elte.hu, ijc@hellion.org.uk Subject: Re: early fixmap causes kmap breakage References: <20081218211543.GB10681@wotan.suse.de> <20081229151731.2a2c5a02.akpm@linux-foundation.org> <20081230040118.GA27679@wotan.suse.de> Date: Mon, 29 Dec 2008 22:22:12 -0800 In-Reply-To: <20081230040118.GA27679@wotan.suse.de> (Nick Piggin's message of "Tue, 30 Dec 2008 05:01:18 +0100") Message-ID: User-Agent: Gnus/5.110006 (No Gnus v0.6) Emacs/21.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-XM-SPF: eid=;;;mid=;;;hst=mx04.mta.xmission.com;;;ip=24.130.11.59;;;frm=ebiederm@xmission.com;;;spf=neutral X-SA-Exim-Connect-IP: 24.130.11.59 X-SA-Exim-Rcpt-To: npiggin@suse.de, ijc@hellion.org.uk, mingo@elte.hu, tglx@linutronix.de, linux-kernel@vger.kernel.org, akpm@linux-foundation.org X-SA-Exim-Mail-From: ebiederm@xmission.com X-SA-Exim-Version: 4.2.1 (built Thu, 07 Dec 2006 04:40:56 +0000) X-SA-Exim-Scanned: No (on mx04.mta.xmission.com); Unknown failure Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Nick Piggin writes: > On Mon, Dec 29, 2008 at 03:17:31PM -0800, Andrew Morton wrote: >> On Thu, 18 Dec 2008 22:15:43 +0100 >> Nick Piggin wrote: >> >> > Hi, >> > >> > I've debugged a problem where i386+pae systems with more than a few CPUs >> > blow up at boot in the kmap_atomic code. >> >> ping? > > No further progress here, I'm waiting on input for how to fix this > "nicely". Meantime, clearing the early fixmap pte I guess works, but > you lose a page... is it possible to put it into .initdata or is > there some issue with that? (I guess on a PAE kernel, 4K isn't a > big deal). > > >> > The problem is that the kmap_atomic pte pages all need to be contiguous >> > memory because the pte is calculated via the first kmap pte page + an >> > offset (so as not to have to walk the page tables every time). >> > >> > The fixmap setup code crudely allocates contiguous pte pages, which is fine, >> > but if it finds an already populated pmd entry, then it will not switch it >> > to a new, contiguous pte page. So the early fixmap introduces a discontig >> > page table right in the middle of the kmap atomic fixmaps. Where is this? >> > Commenting out the eaarly fixmap setup in head_32.S gets everything working >> > properly. What would be the best way to fix this? Could we put the early >> > fixmap page table in initdata, and then have the fixmap setup proper first >> > clear its corresponding pmd entry? Why would we want or need to? >> How come users/testers aren't reporting this? > > Because apparently nobody tests 32-bit PAE systems with more than a couple > of CPUs anymore. This bug comes from HW vendor doing testing of SLES11. Hmm. I have taken a quick skim and I am not seeming the part of the code you are talking about. Is the problem code in mainline? I'm guessing it has something to do with reserve_top_address() being called with a bad value in the normal case. But I don't see it being called at all in the normal case. Eric