From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753790AbYL3EBa (ORCPT ); Mon, 29 Dec 2008 23:01:30 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752626AbYL3EBW (ORCPT ); Mon, 29 Dec 2008 23:01:22 -0500 Received: from mx2.suse.de ([195.135.220.15]:40287 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752483AbYL3EBV (ORCPT ); Mon, 29 Dec 2008 23:01:21 -0500 Date: Tue, 30 Dec 2008 05:01:18 +0100 From: Nick Piggin To: Andrew Morton Cc: ebiederm@xmission.com, linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@elte.hu, ijc@hellion.org.uk Subject: Re: early fixmap causes kmap breakage Message-ID: <20081230040118.GA27679@wotan.suse.de> References: <20081218211543.GB10681@wotan.suse.de> <20081229151731.2a2c5a02.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20081229151731.2a2c5a02.akpm@linux-foundation.org> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > > > > 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? > > 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.