Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757420AbXELWFa (ORCPT ); Sat, 12 May 2007 18:05:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754567AbXELWFX (ORCPT ); Sat, 12 May 2007 18:05:23 -0400 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:51864 "EHLO ebiederm.dsl.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751998AbXELWFX (ORCPT ); Sat, 12 May 2007 18:05:23 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: "H. Peter Anvin" Cc: Alexander van Heukelum , "Antonino A. Daplas" , Andi Kleen , Andrew Morton , Matt Domsch , Vivek Goyal , James Bottomley , Linux Kernel Mailing List Subject: Re: x86 setup rewrite tree ready for flamage^W review References: <464158E9.2000207@zytor.com> <1178806235.18785.1189115515@webmail.messagingengine.com> <46435F8A.1040203@zytor.com> <20070510220406.GA21110@mailshack.com> <4643A128.30302@zytor.com> <20070512122137.GA25944@mailshack.com> <464602DC.4050603@zytor.com> <46460E9E.9020308@zytor.com> Date: Sat, 12 May 2007 16:04:27 -0600 In-Reply-To: <46460E9E.9020308@zytor.com> (H. Peter Anvin's message of "Sat, 12 May 2007 11:59:42 -0700") Message-ID: User-Agent: Gnus/5.110006 (No Gnus v0.6) Emacs/21.4 (gnu/linux) 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 Content-Length: 1113 Lines: 30 "H. Peter Anvin" writes: > Eric W. Biederman wrote: >> >> Even on 386 and 486 class cpus? >> > > Yes, even on 386 and 486 class CPUs. I have personally tested this on > machines as old as the original "double sigma" 386-16. Ok. If you have tested on a wide variety of machines then I won't worry about it. I guess if a cr0 write has always been synchronizing things should be a safe practice. The practical danger is if you write to cr0 and the pipeline is not flushed and the segment loads might execute as 16bit mode segment register loads. I think this is more of a 486 or 586/Pentium danger actually then a 386 one. Hmm. I'm not certain about enabling protected mode but enabling paging at least does appear to be documented to require a jump, before the P6 core. Which may be why it is recommended for initializing protected mode. Eric - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/