From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263517AbTJWJbJ (ORCPT ); Thu, 23 Oct 2003 05:31:09 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263519AbTJWJbE (ORCPT ); Thu, 23 Oct 2003 05:31:04 -0400 Received: from ecbull20.frec.bull.fr ([129.183.4.3]:13453 "EHLO ecbull20.frec.bull.fr") by vger.kernel.org with ESMTP id S263517AbTJWJa7 (ORCPT ); Thu, 23 Oct 2003 05:30:59 -0400 Message-ID: <3F97A009.1C12F466@nospam.org> Date: Thu, 23 Oct 2003 11:31:53 +0200 From: Zoltan Menyhart Organization: Bull S.A. X-Mailer: Mozilla 4.78 [en] (X11; U; AIX 4.3) X-Accept-Language: fr, en MIME-Version: 1.0 To: linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC] prevent "dd if=/dev/mem" crash References: <200310171610.36569.bjorn.helgaas@hp.com> <20031017155028.2e98b307.akpm@osdl.org> <20031019181756.GP1659@openzaurus.ucw.cz> <20031023083316.GB5272@sourcefrog.net> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Some machines may require special memory zones, e.g. for ia64 architectures you need to keep the "minimal state save" area for the Processor Abstraction Layer in un-cached memory. If you read the memory "in the usual way" then you access the memory through the HW caches. The ia64 architecture forbids to have both cached and un-cached access to the same memory location (by any of the CPUs, DMAs), otherwise you create a cache paradox => machine check. Think twice before even trying a "dd if=/dev/mem"... Zoltan Menyhart