From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261922AbUBWPYo (ORCPT ); Mon, 23 Feb 2004 10:24:44 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261923AbUBWPYn (ORCPT ); Mon, 23 Feb 2004 10:24:43 -0500 Received: from smtpq3.home.nl ([213.51.128.198]:49281 "EHLO smtpq3.home.nl") by vger.kernel.org with ESMTP id S261922AbUBWPYl (ORCPT ); Mon, 23 Feb 2004 10:24:41 -0500 Message-ID: <403A1B21.8000100@keyaccess.nl> Date: Mon, 23 Feb 2004 16:24:17 +0100 From: Rene Herman User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.4.1) Gecko/20031029 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Jamie Lokier CC: Coywolf Qi Hunt , "H. Peter Anvin" , linux-kernel@vger.kernel.org Subject: Re: [PATCH] Re: BOOT_CS References: <40375261.6030705@greatcn.org> <20040221163213.GB15991@mail.shareable.org> <403984DD.4030108@greatcn.org> <20040223143056.GC30321@mail.shareable.org> In-Reply-To: <20040223143056.GC30321@mail.shareable.org> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-AtHome-MailScanner-Information: Neem contact op met support@home.nl voor meer informatie X-AtHome-MailScanner: Found to be clean Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Jamie Lokier wrote: > Your patch uses two instructions to flush the queue (push+ret) instead > of one (jmp or ljmp). Is that documented as reliable? No. The current arch manuals seem to say nothing definite, but Intel's 386 manual (ie, the cpu, not the arch) from 1986 explicitly says "after setting PG, a jump must follow immediately". > I can easily imagine an implementation which decodes one instruction > after a mode change predictably, but not two. > > I doubt that it makes a difference - we're setting PG, not changing > the instruction format - but I'd like us to be sure it cannot fail on > things like 386s and 486s, and similar non-Intel chips. I believe you should either keep it as is, do the long jump (although I don't believe that to be necessary: setup.s already long jumped to us) or only delete the indirect jump (we've just been longjumped to, and identity-mapped, so everything would seem to be normalised already). In any case, please jump directly after setting PG. Rene.