From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263435AbUDPRHs (ORCPT ); Fri, 16 Apr 2004 13:07:48 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263565AbUDPRHr (ORCPT ); Fri, 16 Apr 2004 13:07:47 -0400 Received: from mproxy.gmail.com ([216.239.56.247]:2018 "HELO mproxy.gmail.com") by vger.kernel.org with SMTP id S263435AbUDPRHp (ORCPT ); Fri, 16 Apr 2004 13:07:45 -0400 Message-ID: <73CA03E0.6595EF57@mail.gmail.com> Date: Fri, 16 Apr 2004 10:07:44 -0700 From: Ross Biro To: root@chaos.analogic.com Subject: Re: Kernel writes to RAM it doesn't own on 2.4.24 Cc: Linux kernel Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit References: <73979326.58EE2AD2@mail.gmail.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 16 Apr 2004 12:55:33 -0400 (EDT), Richard B. Johnson wrote: > > On Fri, 16 Apr 2004, Ross Biro wrote: > > > mem= isn't there to tell the kernel what ram it owns and what ram it > > doesn't own. It's there to tell the kernel what ram is in the system. > > Since you told the system it only has 500m, it assumes the rest of > > the 3.5G of address space is available for things like memory mapped > > i/o. If you cat /proc/iomem, you'll probably see something has > > reserved the memory range in question. > > > > No! This is address space, not RAM. Whether or not a PCI device > or whatever has internal RAM that's mapped makes no difference. > > I told the kernel that it has 500m of RAM. It better not assume > I don't know what I'm talking about. I might have reserved that > RAM because it's bad or I may have something else important to > do with that RAM (which I do). The problem is that the kernel does assume you know what you are talking about, and you don't. You are abusing the mem= parameter. That's fine, but then you have to tell the kernel what you really mean. What you really want to say is there is memory above 500M and I don't want you to touch it. There may be a way to do that via the fancy mem=@ parameters. What mem= tells the kernel is that there is RAM in a certain spot an no where else. Since you told the kernel there is no ram about 500M, that means that address space is free to be used for memory mapped I/O. Since the kernel trusts you, it started using the memory above 500m for memory mapped i/o. Since you LIED to the kernel, you are getting results you do not like. The solution I settled on was to tell the kernel that people LIE to it and only use memory for I/O if both the BIOS and the USER agree that it's available. You have to find a way to tell the kernel the TRUTH, or you will never get the results you want.