From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932181AbVH3PU4 (ORCPT ); Tue, 30 Aug 2005 11:20:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932185AbVH3PU4 (ORCPT ); Tue, 30 Aug 2005 11:20:56 -0400 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:54945 "EHLO ebiederm.dsl.xmission.com") by vger.kernel.org with ESMTP id S932181AbVH3PUz (ORCPT ); Tue, 30 Aug 2005 11:20:55 -0400 To: Alan Cox Cc: Andrew Morton , linux-kernel@vger.kernel.org, Andi Kleen Subject: Re: [PATCH] i386, x86_64 Initial PAT implementation References: <1125413136.8276.14.camel@localhost.localdomain> From: ebiederm@xmission.com (Eric W. Biederman) Date: Tue, 30 Aug 2005 09:20:19 -0600 In-Reply-To: <1125413136.8276.14.camel@localhost.localdomain> (Alan Cox's message of "Tue, 30 Aug 2005 15:45:36 +0100") Message-ID: User-Agent: Gnus/5.1007 (Gnus v5.10.7) Emacs/21.4 (gnu/linux) 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 Alan Cox writes: > On Llu, 2005-08-29 at 18:20 -0600, Eric W. Biederman wrote: >> ways. Currently this code only allows for an additional flavor >> of uncached access to physical memory addresses which should be hard >> to abuse, and should raise no additional aliasing problems. No >> attempt has been made to fix theoretical aliasing problems. > > Even an uncached/cached alias causes random memory corruption or an MCE > on x86 systems. In fact it can occur even for an alias not in theory > touched by the CPU if it happens to prefetch into or speculate the > address. Right. To the best of my understanding problem aliases are either uncached/write-back or write-combine/write-back. I don't think uncached/write-combine can cause problems. My basic reason for believing this patch is safe is that sane usage will only convert areas of memory that are now uncached to write-combine. > Also be sure to read the PII Xeon errata - early PAT has a bug or two. > > Definitely a much needed improvement to the kernel though. Thanks. As best as I can tell by reading the errata, the only bugs are confined to (a) the upper for PAT entries are used and (b) when mtrrs are disabled and caching is still enabled. I don't make use of either case so my patch should avoid those errata. Eric