Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757374AbXIFLjv (ORCPT ); Thu, 6 Sep 2007 07:39:51 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753616AbXIFLjo (ORCPT ); Thu, 6 Sep 2007 07:39:44 -0400 Received: from main.gmane.org ([80.91.229.2]:41607 "EHLO ciao.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751974AbXIFLjn (ORCPT ); Thu, 6 Sep 2007 07:39:43 -0400 To: Avi Kivity Cc: 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> From: Andi Kleen Date: 06 Sep 2007 13:39:23 +0200 In-Reply-To: <11890207643068-git-send-email-avi@qumranet.com> Message-ID: User-Agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.3 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1173 Lines: 20 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. -Andi - 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/