From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755047AbXKDXI3 (ORCPT ); Sun, 4 Nov 2007 18:08:29 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751729AbXKDXIU (ORCPT ); Sun, 4 Nov 2007 18:08:20 -0500 Received: from gw.goop.org ([64.81.55.164]:40403 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754163AbXKDXIT (ORCPT ); Sun, 4 Nov 2007 18:08:19 -0500 Message-ID: <472E50C5.5020201@goop.org> Date: Sun, 04 Nov 2007 15:07:49 -0800 From: Jeremy Fitzhardinge User-Agent: Thunderbird 2.0.0.5 (X11/20070727) MIME-Version: 1.0 To: Mikael Pettersson CC: hpa@zytor.com, linux-kernel@vger.kernel.org, mingo@redhat.com, tglx@linutronix.de Subject: Re: [PATCH] fix i486 boot failure due to stale %ds References: <200711042158.lA4Lwv9S014628@harpo.it.uu.se> In-Reply-To: <200711042158.lA4Lwv9S014628@harpo.it.uu.se> X-Enigmail-Version: 0.95.5 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Mikael Pettersson wrote: > On Sun, 04 Nov 2007 11:41:58 -0800, H. Peter Anvin wrote: > >> Mikael Pettersson wrote: >> >>> First patch didn't build. Second patch builds and boots Ok. >>> >>> So this means the 486 DX4 has a buggy mov to %cr0? >>> >>> >> Apparently. >> > > Maybe not. I had a look in Intel's SDM Vol3, and the > section "switching to protected mode" specifies that > a move to %cr0 that sets PE should immediately be > followed by a far jmp or call. > Yes, that's what the spec says. I queried this a few months ago, but hpa used his convincing voice and said that in practice it isn't necessary; there are no known cpus which need this, and any that do would cause other things to break. But I guess now we have the counter-example... J