From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755337AbXKDXZx (ORCPT ); Sun, 4 Nov 2007 18:25:53 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754014AbXKDXZq (ORCPT ); Sun, 4 Nov 2007 18:25:46 -0500 Received: from smtp2.linux-foundation.org ([207.189.120.14]:39167 "EHLO smtp2.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753933AbXKDXZp (ORCPT ); Sun, 4 Nov 2007 18:25:45 -0500 Date: Sun, 4 Nov 2007 15:25:06 -0800 (PST) From: Linus Torvalds To: "H. Peter Anvin" cc: Linux Kernel Mailing List , Thomas Gleixner , Ingo Molnar , Mikael Petterson , Eric Biederman Subject: Re: [GIT PULL] x86 setup: correct booting on 486DX4 In-Reply-To: Message-ID: References: <200711042259.lA4Mxa0n025210@tazenda.hos.anvin.org> 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 On Sun, 4 Nov 2007, Linus Torvalds wrote: > > I'm not entirely sure that it needs to be a long-jump, btw. I think any > regular branch is sufficient. You obviously *do* need to make the long > jump later (to reload %cs in protected mode), but I'm not sure it's needed > in that place. I forget the exact rules (but they definitely were > documented). Hmm. The original Linux code did movw $1, %ax lmsw %ax jmp flush_instr flush_instr: and I think that was straigh out of the documentation. So yeah, I think that's the right fix - not a longjmp (which in itself is dangerous: it potentially behaves *differently* on different CPU's, since some CPU's may do the long jump with pre-protected-mode semantics, while others will do it with protected mode already in effect!) Linus