From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761101AbYCUUEn (ORCPT ); Fri, 21 Mar 2008 16:04:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754163AbYCUUEe (ORCPT ); Fri, 21 Mar 2008 16:04:34 -0400 Received: from terminus.zytor.com ([198.137.202.10]:47421 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754047AbYCUUEe (ORCPT ); Fri, 21 Mar 2008 16:04:34 -0400 Message-ID: <47E413B4.5050503@zytor.com> Date: Fri, 21 Mar 2008 12:59:48 -0700 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.12 (X11/20080226) MIME-Version: 1.0 To: Venki Pallipadi CC: ak@muc.de, ebiederm@xmission.com, rdreier@cisco.com, torvalds@linux-foundation.org, gregkh@suse.de, airlied@skynet.ie, davej@redhat.com, mingo@elte.hu, tglx@linutronix.de, akpm@linux-foundation.org, arjan@infradead.org, jesse.barnes@intel.com, linux-kernel@vger.kernel.org, suresh.b.siddha@intel.com Subject: Re: [patch 00/13] x86: PAT support updated - v3 References: <20080319000012.439150000@intel.com> <47E3B84C.6070808@zytor.com> <20080321191921.GA23347@linux-os.sc.intel.com> In-Reply-To: <20080321191921.GA23347@linux-os.sc.intel.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Venki Pallipadi wrote: > On Fri, Mar 21, 2008 at 06:29:48AM -0700, H. Peter Anvin wrote: >> venkatesh.pallipadi@intel.com wrote: >>> * UC_MINUS in PAT to provide backward compatibility to /dem/mem mmap users. >> I have to say I think this looks like a good patchset. However, I'd >> like a bit more clarification with regards to the above point? >> > > X seems to use (in that order) > - mmap the range through /dev/mem > - Set MTRR for the range to WC > > I see this happening on one of my test systems with relatively new xorg. > > In this case, when mmap does the reserve for this range, if we give UC mapping > then we will effectively negate the MTRR WC setting with the range being mapped > UC. To accomodate this special use case, we give /dev/mem mmap (only when there > are no other already existing mappings) a UC_MINUS attribute. With that, > if and when X sets MTRR the range will become WC and until that time it will be > UC. We ensure that all page table mappings use UC_MINUS for that range. > > Long term, we want X to switch to /proc/ of /sys interfaces. But, we can also > provide backward compatibility for existing X usage like above. > Makes total sense. Eventually I think we want to do /proc/mtrr emulation, but for now, this is probably the best option. -hpa