From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754967AbZBTESQ (ORCPT ); Thu, 19 Feb 2009 23:18:16 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753106AbZBTER7 (ORCPT ); Thu, 19 Feb 2009 23:17:59 -0500 Received: from smtp1.linux-foundation.org ([140.211.169.13]:59269 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753062AbZBTER6 (ORCPT ); Thu, 19 Feb 2009 23:17:58 -0500 Date: Thu, 19 Feb 2009 20:17:04 -0800 (PST) From: Linus Torvalds X-X-Sender: torvalds@localhost.localdomain To: Steven Rostedt cc: Huang Ying , Thomas Gleixner , Ingo Molnar , Linux Kernel Mailing List , Andrew Morton , Peter Zijlstra , Frederic Weisbecker , Arjan van de Ven , Rusty Russell , Mathieu Desnoyers , "H. Peter Anvin" Subject: Re: [git pull] changes for tip, and a nasty x86 page table bug In-Reply-To: Message-ID: References: <20090220011316.379904625@goodmis.org> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 19 Feb 2009, Steven Rostedt wrote: > > Is this something worthy of 29? I could whip up a patch against your > latest tree. I think it's a real issue, but I do have to admit that I don't see why it would only trigegr for you. Is it just because the trace stuff ends up setting pages to RW, and you have to have had a lot of read-only stuff to get a whole read-only PMD to begin with? So there's two things that make me nervous: - I do think the KERNPG_TABLE thing is the right thing, and I _think_ that code is just confused, and we should just do KERNPG_TABLE rather than play with confused bits one by one (PRESENT, RW, NX) to the point of just making for more confusion. But I'd like some of the people involved with that code confirm that. Either a "Yeah, we were just confused" or "No, there's this really subtle thing going on, liek this: ..." - The fact that apparently you're the first one to hit this. I realize that you do odd things with ftrace. Was it the fact that you made the "set_memory_ro()" area larger, and then more dynamically mark it back to read-write that you hit it? Haven't we done things like that before? But that said, I'd love to fix this for 2.6.29, especially if somebody can resolve the two worries above. I do _not_ want to take your patch that makes confused code even more confused, unless somebody really explains why a pure KERNPG_TABLE isn't right. Linus