From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761278AbZATMHo (ORCPT ); Tue, 20 Jan 2009 07:07:44 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758817AbZATMHN (ORCPT ); Tue, 20 Jan 2009 07:07:13 -0500 Received: from ns.suse.de ([195.135.220.2]:59306 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758330AbZATMHL (ORCPT ); Tue, 20 Jan 2009 07:07:11 -0500 Date: Tue, 20 Jan 2009 13:07:09 +0100 From: Nick Piggin To: Ingo Molnar Cc: Linux Kernel Mailing List , Linus Torvalds Subject: Re: [patch] x86: optimise page fault entry Message-ID: <20090120120709.GF19505@wotan.suse.de> References: <20090120032426.GE16304@wotan.suse.de> <20090120100946.GA7886@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090120100946.GA7886@elte.hu> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 20, 2009 at 11:09:46AM +0100, Ingo Molnar wrote: > > * Nick Piggin wrote: > > > Hi, > > > > Sorry for the delay with this. The kernel ended up unbootable for me > > when I last dusted off the patch, so I couldn't test it and then > > promptly got sidetracked with other things. > > > > Anyway, this one is tested with a boot, some basic segfault sigbus etc > > tests, and passes various of the mmap and mprotect etc. ltp tests. > > > > Ingo, would you merge this into the x86 tree, please? (unless Linus has > > any objections to this version) > > -tip testing found a 32-bit boot regression, caused by this patch. The > bootup hangs early, during the WP write-test check: > > [ 0.004000] .data : 0xc0691f05 - 0xc09c746c (3285 kB) > [ 0.004000] .text : 0xc0100000 - 0xc0691f05 (5703 kB) > [ 0.004000] Checking if this processor honours the WP bit even in supervisor mode... > > i've excluded x86/mm from tip/master for now, you can find the broken tree > in the tip/tip.x86.mm.broken [v2.6.29-rc2-1069-g583f1b9] branch that i > just pushed out: > > git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git tip.x86.mm.broken Gah, I knew I should have tested with 32-bit. Sorry, I had actually tested it at some point, so I must have dropped this hunk along the way :( > Also, a patch structure sidenote, the diffstat is rather large: > > arch/x86/mm/fault.c | 436 ++++++++++++++++++++++++++++++--------------------- > 1 files changed, 255 insertions(+), 181 deletions(-) > > this shuffles 300 lines of highly critical x86 code around - which makes > me nervous. A finegrained, bisectable series would be far more debuggable. > Had we such a lineup i could have auto-bisected it for you already - while > now you have to see which bit of the ~500 lines of code flux broke the > 32-bit WP test. > > This hang might be easy to find and fix (the WP detect logic is simple), > but other failure modes might be less debuggable and this codepath deals > with a lot of obscure details like CPU errata. So it would be really nice > to have a finegrained splitup of this patch. I guess breaking out the shuffling of parameters (where this bug lies), breaking out functions from do_page_fault, and added branch annotations could be done.... that would still leave a fair hunk in the breakout patch, which I didn't see a really pleasing way to split out. > Three separate testsystems triggered this hang so it should be readily > reproducible. Yes, thanks, Nick --- arch/x86/mm/fault.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) Index: linux-2.6/arch/x86/mm/fault.c =================================================================== --- linux-2.6.orig/arch/x86/mm/fault.c +++ linux-2.6/arch/x86/mm/fault.c @@ -828,7 +828,7 @@ void __kprobes do_page_fault(struct pt_r return; /* Can handle a stale RO->RW TLB */ - if (spurious_fault(address, error_code)) + if (spurious_fault(error_code, address)) return; /*