From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andreas Schwab Subject: Re: why the PAGE_OFFSET is not 0xc0000000 on m68k platform Date: Thu, 21 May 2009 13:29:44 +0200 Message-ID: References: <4A14D5E5.9070103@freescale.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail-out.m-online.net ([212.18.0.10]:49717 "EHLO mail-out.m-online.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752451AbZEUL3r (ORCPT ); Thu, 21 May 2009 07:29:47 -0400 In-Reply-To: <4A14D5E5.9070103@freescale.com> (Lanttor's message of "Thu, 21 May 2009 12:17:41 +0800") Sender: linux-m68k-owner@vger.kernel.org List-Id: linux-m68k@vger.kernel.org To: Lanttor Cc: linux-m68k@vger.kernel.org Lanttor writes: > In my understanding, the kernel page mapping depends on PAGE_OFFSET. > For example, if PAGE_OFFSET is 0x00000000 (assuming 256M memory), the > kernel virtual address will be at (0x00000000 - 0x10000000), right? On m68k, the kernel virtual addresses are in a separate address space from user space, thus the value of PAGE_OFFSET is somewhat arbitrary. > Could this incur some side effect? I see the definition of PAGE_OFFSET > is 0xc0000000 on much platforms. On those platforms kernel and user space share the same address space, and PAGE_OFFSET makes sure that they don't overlap. Andreas. -- Andreas Schwab, schwab@linux-m68k.org GPG Key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5 "And now for something completely different."