From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755007AbXKDXxy (ORCPT ); Sun, 4 Nov 2007 18:53:54 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752867AbXKDXxq (ORCPT ); Sun, 4 Nov 2007 18:53:46 -0500 Received: from terminus.zytor.com ([198.137.202.10]:60787 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754093AbXKDXxp (ORCPT ); Sun, 4 Nov 2007 18:53:45 -0500 Message-ID: <472E5AB6.40509@zytor.com> Date: Sun, 04 Nov 2007 15:50:14 -0800 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.5 (X11/20070727) MIME-Version: 1.0 To: Jeremy Fitzhardinge CC: Mikael Pettersson , linux-kernel@vger.kernel.org, mingo@redhat.com, tglx@linutronix.de, Linus Torvalds Subject: Re: [PATCH] fix i486 boot failure due to stale %ds References: <200711042158.lA4Lwv9S014628@harpo.it.uu.se> <472E50C5.5020201@goop.org> In-Reply-To: <472E50C5.5020201@goop.org> Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Jeremy Fitzhardinge wrote: >> 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... Joy. Apparently the Intel documentation is actually self-inconsistent. Section 9.9.1, page 9-17 does indeed have the "far jump or call" injunction, whereas the sample code in section 9.10.1, page 9-27, line 180 does a near jump! -hpa