From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752398Ab1GVQQ7 (ORCPT ); Fri, 22 Jul 2011 12:16:59 -0400 Received: from terminus.zytor.com ([198.137.202.10]:51334 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751578Ab1GVQQ6 (ORCPT ); Fri, 22 Jul 2011 12:16:58 -0400 Message-ID: <4E29A20C.70402@zytor.com> Date: Fri, 22 Jul 2011 09:15:08 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.18) Gecko/20110621 Fedora/3.1.11-1.fc15 Thunderbird/3.1.11 MIME-Version: 1.0 To: Michal Hocko CC: Venki Pallipadi , x86@kernel.org, linux-kernel@vger.kernel.org, Ingo Molnar Subject: Re: [PATCH] x86, PAT: honor CONFIG_STRICT_DEVMEM if pat is disable] References: <20110722091151.GA4004@tiehlicka.suse.cz> In-Reply-To: <20110722091151.GA4004@tiehlicka.suse.cz> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/22/2011 02:11 AM, Michal Hocko wrote: > Hi, > I have just come across a strange behavior of /dev/[k]mem when PAT is > configured while STRICT_DEVMEM is disabled. > One would expect that /dev/kmem would allow to access also the > system RAM in that configuration but that is not obviously true as pat > code defines range_is_allowed to protect from accessing that memory. > > AFAICS this behavior was introduced in 0124cecf (x86, PAT: disable > /dev/mem mmap RAM with PAT) which says that it disables [k]mem with PAT > because it is safer. There is no explanation why it allows to access > that memory if CONFIG_NONPROMISC_DEVMEM (CONFIG_STRICT_DEVMEM now). > > The thing is even more complicated by the fact that the access is > allowed when nopat kernel parameter is specified because > range_is_allowed just does't call devmem_is_allowed in that case. > > While I do agree that the feature is not safe in general we should honor > STRICT_DEVMEM setting in some way IMO. > > What do you think about the following fix? I have tried to preserve > "disabled for PAT" by default behavior. The reason it is disabled for PAT is that it is very hard to track maps of that memory that are created by mapping /dev/[k]mem, since those maps don't have a defined PAT type and really should be transparently tracking the consensus caching type; this is a facility that *could* be created but has no other user. -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf.