From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932390AbVJDL74 (ORCPT ); Tue, 4 Oct 2005 07:59:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932383AbVJDL74 (ORCPT ); Tue, 4 Oct 2005 07:59:56 -0400 Received: from zproxy.gmail.com ([64.233.162.204]:6092 "EHLO zproxy.gmail.com") by vger.kernel.org with ESMTP id S932377AbVJDL7z (ORCPT ); Tue, 4 Oct 2005 07:59:55 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=beta; d=gmail.com; h=received:message-id:date:from:user-agent:x-accept-language:mime-version:to:cc:subject:content-type:content-transfer-encoding; b=q3M0qq7krpR7DFCrZuk6DU+V/YG2aK7YFSkMTWZ0VaOH80F5x3MwQILsBpCKC2ZEo4v1XcPXeR/ODDbbCzZUYWbKaZAcM5a+hKp6guyDspMebj8Bsv1/O1lukln7BVaoEKlm/z45NWWNbtCyTYXBrvRPhYWkSHNhTXmoQmGROjs= Message-ID: <43426EB4.6080703@gmail.com> Date: Tue, 04 Oct 2005 20:59:48 +0900 From: Tejun Heo User-Agent: Debian Thunderbird 1.0.6 (X11/20050803) X-Accept-Language: en-us, en MIME-Version: 1.0 To: Andi Kleen CC: lkml Subject: Question regarding x86_64 __PHYSICAL_MASK_SHIFT Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hello, Andi. In include/asm-x86_64/page.h, __VIRTUAL_MASK_SHIFT is defined as 48 bits which is the size of virtual address space on current x86_64 machines as used as such. OTOH, __PHYSICAL_MASK_SHIFT is defined as 46 and used as mask shift for physical page address (i.e. physaddr >> 12). In addition to being a bit confusing due to similar names but different meanings, this means that we assume processors can physically address 58 (46 + 12) bits, but both amd64 and IA-32e manuals say that current architectural limit is 52 bits and bits 52-62 are reserved in all page table entries. This currently (and in foreseeable future) doesn't cause any problem but it's still a bit weird. Am I missing something? Thanks. -- tejun