From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757335Ab2DIRxq (ORCPT ); Mon, 9 Apr 2012 13:53:46 -0400 Received: from terminus.zytor.com ([198.137.202.10]:38616 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753710Ab2DIRxp (ORCPT ); Mon, 9 Apr 2012 13:53:45 -0400 Message-ID: <4F832203.1010104@zytor.com> Date: Mon, 09 Apr 2012 10:53:07 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.1) Gecko/20120209 Thunderbird/10.0.1 MIME-Version: 1.0 To: Miles Fidelman CC: Matthew Garrett , linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.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> <4F831BD0.3010707@meetinghouse.net> In-Reply-To: <4F831BD0.3010707@meetinghouse.net> X-Enigmail-Version: 1.4 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/09/2012 10:26 AM, Miles Fidelman wrote: > 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. > Actually this code already exists; the difference is that we have to return to 32-bit mode first. -hpa