From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763495AbYEFPVT (ORCPT ); Tue, 6 May 2008 11:21:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757330AbYEFPVI (ORCPT ); Tue, 6 May 2008 11:21:08 -0400 Received: from terminus.zytor.com ([198.137.202.10]:46473 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754974AbYEFPVH (ORCPT ); Tue, 6 May 2008 11:21:07 -0400 Message-ID: <4820767D.8040202@zytor.com> Date: Tue, 06 May 2008 08:17:17 -0700 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.12 (X11/20080226) MIME-Version: 1.0 To: Ingo Molnar CC: Mikael Pettersson , tglx@linutronix.de, mingo@redhat.com, venkatesh.pallipadi@intel.com, linux-kernel@vger.kernel.org Subject: Re: 2.6.26-rc1 lies about PAT not being available References: <18464.5177.649312.999486@harpo.it.uu.se> <20080506114839.GD32591@elte.hu> In-Reply-To: <20080506114839.GD32591@elte.hu> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Ingo Molnar wrote: >> I know about Intel's PAT erratum (only 4 PAT entries work) and >> understand that the kernel might not want to use a half-broken PAT >> implementation, but the statement above is blatantly false: the kernel >> IS built with PAT support and the CPU DOES have (half-broken) PAT HW >> support as /proc/cpuinfo from earlier kernels confirms. > > well the code is just being overly conservative, and the message is > right: the kernel does not support PAT on that hw. Yet. > > Please send us a patch and test whether it's working on your box? That's > how the PAT code evolved: it initially was only enabled on a very small > subset of CPUs. We can enable it on more CPUs if people test it. > > To be conservative, please make the code emit a printk that this is PAT > on not fully-working hw platform (only 4 PAT entries work). If there > _is_ some erratum on that CPU affecting PAT reliability down the line, > we at least want to have some clue in the syslog. > For what it's worth, we only use four PAT entries, so it doesn't matter that only four work. -hpa