From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758126Ab2CCBRx (ORCPT ); Fri, 2 Mar 2012 20:17:53 -0500 Received: from terminus.zytor.com ([198.137.202.10]:48343 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755094Ab2CCBRw (ORCPT ); Fri, 2 Mar 2012 20:17:52 -0500 Message-ID: <4F517133.5070504@zytor.com> Date: Fri, 02 Mar 2012 17:17:39 -0800 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.1) Gecko/20120209 Thunderbird/10.0.1 MIME-Version: 1.0 To: Linus Torvalds CC: Andi Kleen , Linux Kernel Mailing List , linux-fsdevel , Al Viro Subject: Re: Word-at-a-time dcache name accesses (was Re: .. anybody know of any filesystems that depend on the exact VFS 'namehash' implementation?) References: <4F516811.8060800@zytor.com> <4F516DBA.2030809@zytor.com> In-Reply-To: X-Enigmail-Version: 1.3.5 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/02/2012 05:11 PM, Linus Torvalds wrote: > On Fri, Mar 2, 2012 at 5:02 PM, H. Peter Anvin wrote: >> >> Note that does mean we need a guard page after each and every >> discontiguous RAM range, not just the last one. Raising that issue >> since we have had serious bugs in that area in the past. > > Are you sure? I didn't think we even *mapped* things at that granularity. > > We only really need a guard page at the end of an actual end-of-ram > where we no longer have page tables and/or could hit device space. > Yes of course. Note that I'm currently pushing for mapping only RAM regions; we have a lot of bugs and workarounds related to mapping too much, and the answer to fixing that should be pretty obvious. > For robustness and actual deployment, I do think that yes, we do want > to make it an explicit rule. Definitely. Ideally those pages should be zeroed and mapped readonly. -hpa