Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762475AbXJOLHq (ORCPT ); Mon, 15 Oct 2007 07:07:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758559AbXJOLHj (ORCPT ); Mon, 15 Oct 2007 07:07:39 -0400 Received: from one.firstfloor.org ([213.235.205.2]:56023 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757094AbXJOLHi (ORCPT ); Mon, 15 Oct 2007 07:07:38 -0400 Date: Mon, 15 Oct 2007 13:07:35 +0200 From: Andi Kleen To: Nick Piggin Cc: Andi Kleen , David Chinner , Jeremy Fitzhardinge , xfs@oss.sgi.com, Xen-devel , Linux Kernel Mailing List , Mark Williamson , Morten =?iso-8859-1?B?QsO4Z2Vza292?= , xfs-masters@oss.sgi.com Subject: Re: Interaction between Xen and XFS: stray RW mappings Message-ID: <20071015110735.GA11748@one.firstfloor.org> References: <470FA7C3.90404@goop.org> <20071014225618.GN23367404@sgi.com> <200710160056.47458.nickpiggin@yahoo.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200710160056.47458.nickpiggin@yahoo.com.au> User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1159 Lines: 30 On Tue, Oct 16, 2007 at 12:56:46AM +1000, Nick Piggin wrote: > Is this true even if you don't write through those old mappings? I think it happened for reads too. It is a little counter intuitive because in theory the CPU doesn't need to write back non dirty lines, but in the one case which took so long to debug exactly this happened somehow. At it is undefined for reads and writes in the architecture so better be safe than sorry. And x86 CPUs are out of order and do speculative executation and that can lead to arbitary memory accesses even if the code never touches an particular address. Newer Intel CPUs have something called self-snoop which was supposed to handle this; but in some situations it doesn't seem to catch it either. > Is DRM or AGP then not also broken with lazy highmem flushing, or > how do they solve that? AGP doesn't allocate highmem pages. Not sure about the DRM code. -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/