From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753389AbaBYRQY (ORCPT ); Tue, 25 Feb 2014 12:16:24 -0500 Received: from terminus.zytor.com ([198.137.202.10]:57761 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753173AbaBYRQX (ORCPT ); Tue, 25 Feb 2014 12:16:23 -0500 Message-ID: <530CCFD2.3050007@zytor.com> Date: Tue, 25 Feb 2014 09:16:02 -0800 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Dave Jones , Chris Bainbridge , x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] x86: set Pentium M as PAE capable References: <20140225060146.GA4339@debian.local> <530C7465.2080600@zytor.com> <20140225162611.GA31902@redhat.com> In-Reply-To: <20140225162611.GA31902@redhat.com> X-Enigmail-Version: 1.6 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/25/2014 08:26 AM, Dave Jones wrote: > On Tue, Feb 25, 2014 at 02:45:57AM -0800, H. Peter Anvin wrote: > > On 02/24/2014 10:01 PM, Chris Bainbridge wrote: > > > Pentium M is PAE capable but does not indicate so in the CPUID response. > > > This is an issue now that some distributions are no longer shipping > > > non-PAE kernels (those distributions no longer boot on Pentium M). This > > > small patch fixes the issue by forcing the PAE capability on Pentium M. > > > > > > For more discussion see https://bugs.launchpad.net/baltix/+bug/930447 > > > > > > > 1. This patch doesn't match the discussion in the link. > > 2. You would have to also enable this in the cpu testing code in > > arch/x86/boot. > > 3. At the very least we need to print a serious warning that the CPU > > is being run outside its specifications. I have no personal > > information about why this CPUID bit was disabled, but it could be > > that it was discovered in testing that it didn't work correctly in > > all circumstances (e.g. high temperature.) This is very much "use > > at your own risk..."; you could get data corruption or even > > hardware damage. > > About six years ago, we almost went down this same path for Fedora, > and I'm fairly sure the only reason we backed off and decided to not > pursue it was that we found some Pentium M's where it just didn't work. > OK, that *definitely* means that if we're doing this at all we're doing it via an explicit opt-in on the command line, and tainting the kernel in the process. I don't know if anyone (Chris?) is interested enough in the problem to do such a patch, though. I know I'm not too interested in spending a bunch of time on. -hpa