From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S266894AbUIXDj7 (ORCPT ); Thu, 23 Sep 2004 23:39:59 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S266196AbUIXDfn (ORCPT ); Thu, 23 Sep 2004 23:35:43 -0400 Received: from holomorphy.com ([207.189.100.168]:31196 "EHLO holomorphy.com") by vger.kernel.org with ESMTP id S267666AbUIXDee (ORCPT ); Thu, 23 Sep 2004 23:34:34 -0400 Date: Thu, 23 Sep 2004 20:29:28 -0700 From: William Lee Irwin III To: John Fusco Cc: Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: [vm 0/4] replace remap_page_range() with remap_pfn_range() Message-ID: <20040924032928.GR9106@holomorphy.com> References: <41535AAE.6090700@yahoo.com> <20040924021735.GL9106@holomorphy.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20040924021735.GL9106@holomorphy.com> Organization: The Domain of Holomorphy User-Agent: Mutt/1.5.6+20040722i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 23, 2004 at 06:22:22PM -0500, John Fusco wrote: >> Everything worked great until we decided that we needed to install 6GB >> in this system. The problem is that remap_page_range() uses an unsigned >> long as the parameter for a physical address. On IA32, an unsigned long >> is 32-bits, but the IA32 is capable of addressing well over 4GB of RAM. >> So physical addresses on IA32 must be larger than 32 bits. On Thu, Sep 23, 2004 at 07:17:35PM -0700, William Lee Irwin III wrote: > Do these patches work for you? Compiletested on sparc64. Long-format changelog: Resolve physical address overflow issue in the remap_page_range() API by replacing it with remap_pfn_range(), which accepts its physical address argument as a pfn, hence allowing the use of a single-precision physical address argument without the risk of overflow at the API boundary. The above issue has hobbled support for various 32-bit architectures, including some embedded systems (ppc440 IIRC), caused persistent portability issues for sound drivers for legacy systems (sparc32; unfortunately this patch alone does not fully resolve those), and according to John Fusco's reports, made drivers for some PCI-X hardware infeasible to port to recent ia32 PAE enterprise systems. With this patch series applied, physical address overflows on 32-bit systems caused directly by remap_page_range() are gone forever, and ca. 100LOC of cut-and-waste driver code are swept out of existence alongside them. -- wli P.S.: The existing solution to the sparc32 issue was to pass a double precision representation of the physical address as 2 single- precision arguments in an API (io_remap_page_range()) whose argument corresponding to those two was a single single- precision argument on most/all other architectures. The sparc32-specific issue requires more work beyond these patches to rectify. The most apparent consequence of the API skew is that drivers don't compile on sparc32 when they use io_remap_page_range() due to passing insufficient arguments, or vice-versa for drivers originally written for sparc32.