Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263269AbUDPP5X (ORCPT ); Fri, 16 Apr 2004 11:57:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263371AbUDPP5X (ORCPT ); Fri, 16 Apr 2004 11:57:23 -0400 Received: from chaos.analogic.com ([204.178.40.224]:1152 "EHLO chaos.analogic.com") by vger.kernel.org with ESMTP id S263269AbUDPPzY (ORCPT ); Fri, 16 Apr 2004 11:55:24 -0400 Date: Fri, 16 Apr 2004 11:55:28 -0400 (EDT) From: "Richard B. Johnson" X-X-Sender: root@chaos Reply-To: root@chaos.analogic.com To: Linux kernel Subject: Kernel writes to RAM it doesn't own on 2.4.24 Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1739 Lines: 45 Hello again, If I start a system that has 1 Gb of memory with mem=500m, the value of the kernel's num_physpages is 0x20000 as would be expected. If I multiply that by PAGE_SIZE, I get 0x20000000, also as expected. If I observe that memory region, I note that somebody has written something there! This is not good. The kernel touches RAM it doesn't own. I have booted the system with only the internal floppy controller and no other modules installed. I see the same thing. Script started on Fri Apr 16 11:33:39 2004 # monitor TMD Platinum(tm) Control System Version 2.0 Copyright(c) 1999-2003, Analogic Corporation Enter "help" for commands PLATINUM> dump=20000000 20000000 78 56 34 12 21 43 65 87-FF FF FF FF FF FF FF FF xV4.!Ce......... 20000010 FF FF FF FF FF FF FF FD-FF FF FF FF FF FF FF FF ................ 20000020 FF FF FF FF FF FE FF FF-FF FF FE FF FF FF FF FF ................ [SNIPPED...] My temporary work around for the kernel's destroying a precious DMA buffer is to start one page higher. However, whomever is writing to that RAM is likely writing other places it doesn't belong also. This could lead to some very interesting bugs. Note that the value written there is 0x12345678, twice, once in little endian and another in swap-nibble big endian, like a mirror. This is evil. Cheers, Dick Johnson Penguin : Linux version 2.4.24 on an i686 machine (5596.77 BogoMips). Note 96.31% of all statistics are fiction. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/