From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754769AbXKEVKi (ORCPT ); Mon, 5 Nov 2007 16:10:38 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751925AbXKEVKa (ORCPT ); Mon, 5 Nov 2007 16:10:30 -0500 Received: from terminus.zytor.com ([198.137.202.10]:55286 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750950AbXKEVKa (ORCPT ); Mon, 5 Nov 2007 16:10:30 -0500 Message-ID: <472F85F2.6040501@zytor.com> Date: Mon, 05 Nov 2007 13:06:58 -0800 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.5 (X11/20070727) MIME-Version: 1.0 To: Jeremy Fitzhardinge CC: "Eric W. Biederman" , Linus Torvalds , Linux Kernel Mailing List , Thomas Gleixner , Ingo Molnar , Mikael Petterson Subject: Re: [GIT PULL] x86 setup: correct booting on 486 (revised) References: <200711050358.lA53wlho003349@tazenda.hos.anvin.org> <472F5941.2060507@zytor.com> <472F61C8.4040300@zytor.com> <472F7D8D.8050505@zytor.com> <472F826E.3050008@goop.org> In-Reply-To: <472F826E.3050008@goop.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Jeremy Fitzhardinge wrote: > H. Peter Anvin wrote: >> Nailing down the interface as hard as possible is a good idea, to >> avoid tying your hands for the future. > > Erm, I guess I see what you mean, but it comes to the effect of tying > your hands now in a specific way, rather than having them tied in an > unknown way later on... Sort of. The problem is you can frequently not > But I hadn't noticed the 32-bit boot protocol spec go in. Unfortunately > it isn't useful for booting a pv Xen guest; I just mailed my comments. > I hope we can iterate this to something more generally useful before > getting too wedded to the current protocol. I'm not so sure about that. Xen PV is rather fundamentally a different beast, hence the platform field recently added to the protocol. > 2. Also, Xen reserves the last chunk of the GDT for its own > descriptors, and by default boots the guest with the segment > registers preloaded with selectors pointing to flat 4G descriptors > in this range. These segments are not a full 4G, since it uses > segment limits to protect the hypervisor from guests. The limits > are as large as they can possibly be. I like to see the boot > protocol require that all segments registers are preloaded with > large flat 32-bit descriptors, but not require a specific selector > value. I'd happy to require the GDT to be active, so the segment > registers can be reloaded with their current values, until the > kernel establishes its own GDT. This is addressed by the "don't reload segments" bit in LOADFLAGS. -hpa