Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755974AbXJVSlW (ORCPT ); Mon, 22 Oct 2007 14:41:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755430AbXJVSky (ORCPT ); Mon, 22 Oct 2007 14:40:54 -0400 Received: from gw.goop.org ([64.81.55.164]:52442 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755406AbXJVSkx (ORCPT ); Mon, 22 Oct 2007 14:40:53 -0400 Message-ID: <471CEEB4.9040807@goop.org> Date: Mon, 22 Oct 2007 11:40:52 -0700 From: Jeremy Fitzhardinge User-Agent: Thunderbird 2.0.0.5 (X11/20070727) MIME-Version: 1.0 To: Andi Kleen CC: dean gaudet , Nick Piggin , Xen-devel , Morten@suse.de, David Chinner , Linux Kernel Mailing List , =?ISO-8859-1?Q?B=F8geskov?= , xfs@oss.sgi.com, xfs-masters@oss.sgi.com, Mark Williamson Subject: Re: Interaction between Xen and XFS: stray RW mappings References: <470FA7C3.90404@goop.org> <20071014225618.GN23367404@sgi.com> <4712A254.4090604@goop.org> <200710151415.07248.nickpiggin@yahoo.com.au> <471C1A61.1010001@goop.org> In-Reply-To: X-Enigmail-Version: 0.95.3 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1320 Lines: 31 Andi Kleen wrote: > Jeremy Fitzhardinge writes: > >> Yes, that's precisely the problem. xfs does delay the unmap, leaving >> stray mappings, which upsets Xen. >> > > Again it not just upsets Xen, keeping mappings to freed pages is wrong generally > and violates the x86 (and likely others like PPC) architecture because it can > cause illegal caching attribute aliases. > > The patch that went into the tree was really not correct -- this > bogus optimization should have been unconditionally removed > or if you really wanted an ifdef made dependent on !CONFIG_XEN && > !CONFIG_AGP (and likely && !CONFIG_DRM && !CONFIG_anything else that > uses uncached mappings in memory). > > You just worked around the obvious failure and leave the non obvious > rare corruptions in, which isn't a good strategy. Well, at least it becomes a known issue and/or placeholder for when Nick does his grand unified vmap manager. I guess a clean workaround would be to add a CONFIG_XFS_LAZY_UNMAP, and do it at the Kconfig level... I'll cook up a patch. J - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/