From mboxrd@z Thu Jan 1 00:00:00 1970 From: "H. Peter Anvin" Subject: Re: Word-at-a-time dcache name accesses (was Re: .. anybody know of any filesystems that depend on the exact VFS 'namehash' implementation?) Date: Fri, 02 Mar 2012 17:17:39 -0800 Message-ID: <4F517133.5070504@zytor.com> References: <4F516811.8060800@zytor.com> <4F516DBA.2030809@zytor.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: Andi Kleen , Linux Kernel Mailing List , linux-fsdevel , Al Viro To: Linus Torvalds Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.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