From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261570AbTD3Kz3 (ORCPT ); Wed, 30 Apr 2003 06:55:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262013AbTD3Kz3 (ORCPT ); Wed, 30 Apr 2003 06:55:29 -0400 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:20536 "EHLO frodo.biederman.org") by vger.kernel.org with ESMTP id S261570AbTD3Kz2 (ORCPT ); Wed, 30 Apr 2003 06:55:28 -0400 To: Jamie Lokier Cc: Andi Kleen , joe briggs , linux-kernel@vger.kernel.org Subject: Re: software reset References: <200304291037.13598.jbriggs@briggsmedia.com.suse.lists.linux.kernel> <20030430075004.GB13859@mail.jlokier.co.uk> From: ebiederm@xmission.com (Eric W. Biederman) Date: 30 Apr 2003 05:04:59 -0600 In-Reply-To: <20030430075004.GB13859@mail.jlokier.co.uk> Message-ID: User-Agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.1 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Jamie Lokier writes: > Andi Kleen wrote: > > The most reliable way is to force a triple fault; load zero into > > the IDT register and then trigger an exception. The linux kernel > > does that in fact for reboot and so far I haven't seen any machine failing > > to reset yet. > > There are some 486s which don't boot on triple fault, nor on asking > the keyboard controller to pulse the reset line. Hence the 3rd option, > "reboot=bios". And as an interesting data point all a triple fault does on a modern system is to put the cpu in a weird stopped state. Some hardware usually the southbridge then detects this and if properly configured will trigger the reset line. I believe this may actually go back into history as far as the 486 but I have not done the researched to see how far back this behavior goes. Eric