From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752956AbZH1Tt2 (ORCPT ); Fri, 28 Aug 2009 15:49:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752894AbZH1Tt2 (ORCPT ); Fri, 28 Aug 2009 15:49:28 -0400 Received: from sj-iport-1.cisco.com ([171.71.176.70]:24923 "EHLO sj-iport-1.cisco.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752880AbZH1Tt1 (ORCPT ); Fri, 28 Aug 2009 15:49:27 -0400 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: ApoEAIvRl0qrR7O6/2dsb2JhbADBfohAAZAfBYQZ X-IronPort-AV: E=Sophos;i="4.44,292,1249257600"; d="scan'208";a="234603006" From: Roland Dreier To: joe Shmoe Cc: linux-kernel@vger.kernel.org Subject: Re: kernel page table mapping for >1GB <3 GB for x86 arch without PAE References: <812804.57438.qm@web45209.mail.sp1.yahoo.com> X-Message-Flag: Warning: May contain useful information Date: Fri, 28 Aug 2009 12:49:29 -0700 In-Reply-To: <812804.57438.qm@web45209.mail.sp1.yahoo.com> (joe Shmoe's message of "Fri, 28 Aug 2009 11:40:56 -0700 (PDT)") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.0.91 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-OriginalArrivalTime: 28 Aug 2009 19:49:29.0746 (UTC) FILETIME=[A8107F20:01CA2818] Authentication-Results: sj-dkim-2; header.From=rdreier@cisco.com; dkim=pass ( sig from cisco.com/sjdkim2002 verified; ); Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > But my question is with regard to setting up the page tables during the kernel initialization in such a way so that entire RAM upto 4GB can be mapped. i.e virtual to physical address mapping. My question is strictly with reg. to physical address mapping only. > > Why does kernel stop at 1GB (896 MB to be exact) while mapping from linear to physical address. Because it wants to be able to give userspace 3GB of address space. And userspace mapping cannot be a linear mapping to physical memory -- it must be real virtual memory that has proper access permissions and can handle mmap'ed files, shared libraries, etc etc. So userspace cannot share the kernel's linear mapping.