Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752486Ab1FTCmv (ORCPT ); Sun, 19 Jun 2011 22:42:51 -0400 Received: from mail-iy0-f174.google.com ([209.85.210.174]:43896 "EHLO mail-iy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750878Ab1FTCms convert rfc822-to-8bit (ORCPT ); Sun, 19 Jun 2011 22:42:48 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=tOkl6kn9wgNVvK2iM4MlYL7s4qzuRIudZMq0D4EM/9LqMf4nQaYuMT2Bgvl8O85afF hosriWZj84LswSyNUFSGQn1s9X0siwN8+j5YMJtp2/d+kAzaZAyuynRx9su1Pxyz9iaP Vp0Grbes7MrGa+VodECNZt8dTVbyU5rOoVz14= MIME-Version: 1.0 In-Reply-To: <201106171155.32062.ptesarik@suse.cz> References: <201106171038.25988.ptesarik@suse.cz> <20110617093032.GA19235@elte.hu> <201106171155.32062.ptesarik@suse.cz> Date: Mon, 20 Jun 2011 10:42:47 +0800 Message-ID: Subject: Re: [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary physical addresses From: =?UTF-8?Q?Am=C3=A9rico_Wang?= To: Petr Tesarik Cc: Ingo Molnar , 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 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1900 Lines: 42 On Fri, Jun 17, 2011 at 5:55 PM, Petr Tesarik wrote: > Dne Pá 17. června 2011 11:30:32 Ingo Molnar napsal(a): >> * 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. > > Hi Ingo, > >> 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. > > It is still used as a "memory source" by Dave Anderson's crash utility for > live examination of a running system. Redhat has "overcome" the /dev/mem > deficiencies by writing an out-of-tree re-implementation of /dev/mem, which > uses /dev/crash instead. As it is an "unnecessary duplication of an existing > driver", this method was rejected by the project manager here at SUSE. > > The suggested alternative was to enhance (or fix) the existing driver. Without > this patch series there is no way to access high memory. In conjunction with > CONFIG_HIGHPTE, it makes the crash utility near to useless on anything with > high memory, because crash can no longer translate virtual to physical > addresses. > How about /proc/kcore? AFAIK, it can access highmem, but Dave didn't consider it for some reason. -- 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/