Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758092AbXIFNWx (ORCPT ); Thu, 6 Sep 2007 09:22:53 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756216AbXIFNWn (ORCPT ); Thu, 6 Sep 2007 09:22:43 -0400 Received: from main.gmane.org ([80.91.229.2]:50676 "EHLO ciao.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756187AbXIFNWm (ORCPT ); Thu, 6 Sep 2007 09:22:42 -0400 Message-ID: <46DFFE1F.7060900@qumranet.com> Date: Thu, 06 Sep 2007 16:18:23 +0300 From: Avi Kivity User-Agent: Thunderbird 2.0.0.5 (X11/20070719) MIME-Version: 1.0 To: Andi Kleen CC: Avi Kivity , public-linux-kernel-u79uwXL29TY76Z2rM5mHXA@ciao.gmane.org, public-linux-mm-Bw31MaZKKs3YtjvyW6yDsg@ciao.gmane.org, public-kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@ciao.gmane.org, public-general-ZwoEplunGu1OwGhvXhtEPSCwEArCW2h5@ciao.gmane.org Subject: Re: [PATCH][RFC] pte notifiers -- support for external page tables References: <11890207643068-git-send-email-avi@qumranet.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-TMDA-Confirmed: Thu Sep 6 15:22:34 CEST 2007 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1545 Lines: 42 [ugh, what happened to the cc-list?] Andi Kleen wrote: > Avi Kivity writes: > >> pte notifiers are different from paravirt_ops: they extend the normal >> page tables rather than replace them; and they provide high-level information >> such as the vma and the virtual address for the driver to use. >> > > Sounds like a locking horror to me. To do anything with page tables > you need locks. Both for the kernel page tables and for your new tables. > > What happens when people add all > things of complicated operations in these notifiers? That will likely > happen and then everytime you change something in VM code they > will break. This has the potential to increase the cost of maintaining > VM code considerably, which would be a bad thing. > > This is quite different from paravirt ops because low level pvops > can typically run lockless by just doing some kind of hypercall directly. > But that won't work for maintaining your custom page tables. > This is a real problem. I don't have a solution yet. Obviously that needs to be addressed before something like this can go in; but as it's been done for the quadrics driver, presumably it is doable. -- Any sufficiently difficult bug is indistinguishable from a feature. - 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/