Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758862Ab1FQJaz (ORCPT ); Fri, 17 Jun 2011 05:30:55 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:50771 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758833Ab1FQJaw (ORCPT ); Fri, 17 Jun 2011 05:30:52 -0400 Date: Fri, 17 Jun 2011 11:30:32 +0200 From: Ingo Molnar To: Petr Tesarik Cc: Andrew Morton , Fenghua Yu , "H. Peter Anvin" , Ingo Molnar , Paul Mundt , Russell King , Thomas Gleixner , Tony Luck , x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org, linux-kernel@vger.kernel.org, Arjan van de Ven , Dave Jones , Linus Torvalds Subject: Re: [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary physical addresses Message-ID: <20110617093032.GA19235@elte.hu> References: <201106171038.25988.ptesarik@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201106171038.25988.ptesarik@suse.cz> User-Agent: Mutt/1.5.20 (2009-08-17) X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.3.1 -2.0 BAYES_00 BODY: Bayes spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1549 Lines: 42 * Petr Tesarik wrote: > This patch series enhances /dev/mem, so that read and write is > possible at any address. The patchset includes actual > implementation for x86. This series lacks a description of why this is desired. My strong opinion is that it's not desired at all: /dev/mem never worked beyond 4G addresses so by today it has become largely obsolete and is on the way out really. I'm aware of these current /dev/mem uses: - Xorg maps below 4G non-RAM addresses and the video BIOS - It used to have some debugging role but these days kexec and kgdb has largely taken over that role - partly due to the 4G limit. - there's some really horrible out-of-tree drivers that do mmap()s via /dev/mem, those should be fixed if they want to move beyond 4G: their char device should be mmap()able. - all distro kernel's i'm aware of use CONFIG_STRICT_DEVMEM=y, which restricts /dev/mem to non-RAM pages of physical memory. [ With the sad inclusion of the first 1MB, which Xorg needs. ] Are you aware of any legitimate usecases? Frankly, i dont think we ever *want* to 'fix' /dev/mem to support addresses beyond 4G and grow messy userspace (and kernelspace) that somehow relies on that. Thank goodness that we never supported it ... Thanks, Ingo -- 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/