From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750936AbXFVNT5 (ORCPT ); Fri, 22 Jun 2007 09:19:57 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752510AbXFVNTu (ORCPT ); Fri, 22 Jun 2007 09:19:50 -0400 Received: from smtpq1.groni1.gr.home.nl ([213.51.130.200]:51824 "EHLO smtpq1.groni1.gr.home.nl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751299AbXFVNTt (ORCPT ); Fri, 22 Jun 2007 09:19:49 -0400 Message-ID: <467BCB99.8030003@gmail.com> Date: Fri, 22 Jun 2007 15:16:09 +0200 From: Rene Herman User-Agent: Thunderbird 1.5.0.12 (X11/20070509) MIME-Version: 1.0 To: "H. Peter Anvin" CC: Bart Trojanowski , linux-kernel@vger.kernel.org Subject: Re: how to tell linux (on x86) to ignore 1M or memory References: <20070419141804.GO32620@jukie.net> <46290DED.80500@gmail.com> <467B29DA.9040309@zytor.com> In-Reply-To: <467B29DA.9040309@zytor.com> Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit X-AtHome-MailScanner-Information: Please contact support@home.nl for more information X-AtHome-MailScanner: Found to be clean Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On 06/22/2007 03:46 AM, H. Peter Anvin wrote: > Rene Herman wrote: >> On 04/19/2007 04:18 PM, Bart Trojanowski wrote: >> >>> I need to preserve some state from the bios before entering protected >>> mode. For now I want to copy it into some ram accessible by >>> real-mode, say the last megabyte visible in real-mode. >>> >>> What's the easiest way to have linux ignore the megabyte starting at 15M? >> Note that real-mode can only access the first megabyte (*) and not the >> first 16. 16MB is the 16-bit protected mode (286) limit. >> > > No, 16-bit protected mode (on 386+) is not limited to 16 MB. That all depends on one's definition of 16-bit protected mode. The "(286)" after mine meant I was talking about the definition in which descriptors have a 24-bit base (and 16-bit limit) field -- ie, real 286 and arguably, "real 16-bit protected mode". Yes, I guess another valid definition is "code with a 16-bit address and operand size default" on a 386+ and sure, that's just flipping a bit away. In the context of Linux I agree it's also a sensible definition, so, well, whatever. The point was that real mode could only access the first 1M, not the first 16... :-) Rene.