From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932143Ab2DIPwE (ORCPT ); Mon, 9 Apr 2012 11:52:04 -0400 Received: from cavan.codon.org.uk ([93.93.128.6]:48582 "EHLO cavan.codon.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932091Ab2DIPwD (ORCPT ); Mon, 9 Apr 2012 11:52:03 -0400 Date: Mon, 9 Apr 2012 16:51:55 +0100 From: Matthew Garrett To: Miles Fidelman 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? Message-ID: <20120409155155.GA22974@srcf.ucam.org> References: <4F8302B4.8040901@meetinghouse.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4F8302B4.8040901@meetinghouse.net> User-Agent: Mutt/1.5.20 (2009-06-14) X-SA-Exim-Connect-IP: X-SA-Exim-Mail-From: mjg59@cavan.codon.org.uk X-SA-Exim-Scanned: No (on cavan.codon.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > 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? -- Matthew Garrett | mjg59@srcf.ucam.org