From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755839Ab2DIR0o (ORCPT ); Mon, 9 Apr 2012 13:26:44 -0400 Received: from server1.neighborhoods.net ([207.154.13.48]:52757 "EHLO server1.neighborhoods.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753176Ab2DIR0n (ORCPT ); Mon, 9 Apr 2012 13:26:43 -0400 Message-ID: <4F831BD0.3010707@meetinghouse.net> Date: Mon, 09 Apr 2012 13:26:40 -0400 From: Miles Fidelman User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:11.0) Gecko/20120312 Firefox/11.0 SeaMonkey/2.8 MIME-Version: 1.0 To: Matthew Garrett CC: linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, x86@kernel.org, peter.chubb@nicta.com.au, michael.d.labriola@gmail.com Subject: Re: reboot via bios on X86_64? References: <4F8302B4.8040901@meetinghouse.net> <20120409155155.GA22974@srcf.ucam.org> In-Reply-To: <20120409155155.GA22974@srcf.ucam.org> 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 Thanks for the quick response. Matthew Garrett wrote: > On Mon, Apr 09, 2012 at 11:39:32AM -0400, Miles Fidelman wrote: > >> 1. What's the logic behind this? Why not enable a bios reboot for 64bit >> kernels? Is there any reason why the machine_real_restart code wouldn't >> work just as well in 64bit mode? Anybody know the history? > The bios reboot code requires you to reprogram the CPU to real mode. I > don't think there's any fundamental reason you can't do that from 64-bit > mode, but nobody's ever written that code. That would explain it. I guess there's a little bit of trickiness involved in setting things up before switching to real mode. >> 2. Anybody know a workaround, short of patching and compiling a custom >> kernel? Are there other paths through the reboot code that can >> invoke a bios >> reboot? [Note: someone suggested trying a kexec-reboot, but that's also >> not supported on my configuration (running over a Xen hypervisor).] > Windows never uses the equivalent of the BIOS reboot method, so the > assumption is that if you ever need on Linux to it's because there's a > bug somewhere else. Does the platform reboot if you run the kernel on > bare metal rather than under Xen? No. Tried all the combinations - w/ and w/o hypervisor, all the available kernel options. Seems like the only thing that will reboot this particular hardware/bios combo is via the bios. Miles -- In theory, there is no difference between theory and practice. In practice, there is. .... Yogi Berra