Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752439AbbFLAwa (ORCPT ); Thu, 11 Jun 2015 20:52:30 -0400 Received: from cantor2.suse.de ([195.135.220.15]:59327 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750915AbbFLAw0 (ORCPT ); Thu, 11 Jun 2015 20:52:26 -0400 Date: Fri, 12 Jun 2015 02:52:21 +0200 From: "Luis R. Rodriguez" To: Toshi Kani Cc: "Luis R. Rodriguez" , Tomi Valkeinen , Borislav Petkov , Bjorn Helgaas , Jej B , Ville =?iso-8859-1?Q?Syrj=E4l=E4?= , Ville =?iso-8859-1?Q?Syrj=E4l=E4?= , Andrew Morton , "linux-kernel@vger.kernel.org" , linux-media@vger.kernel.org, linux-fbdev , "linux-pci@vger.kernel.org" , Andy Lutomirski , X86 ML , Juergen Gross , Dave Airlie , xen-devel@lists.xenproject.org, Julia Lawall Subject: Re: RIP MTRR - status update for upcoming v4.2 Message-ID: <20150612005221.GD23057@wotan.suse.de> References: <1434064996.11808.64.camel@misato.fc.hp.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1434064996.11808.64.camel@misato.fc.hp.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2139 Lines: 49 On Thu, Jun 11, 2015 at 05:23:16PM -0600, Toshi Kani wrote: > On Thu, 2015-06-11 at 13:36 -0700, Luis R. Rodriguez wrote: > : > > Pending RIP MTRR patches > > ==================== > > > > There are a few pending series so I wanted to provide a status update > > on those series. > > > > mtrr: bury MTRR - unexport mtrr_add() and mtrr_del() > > > > This is the nail on the MTRR coffin, it will prevent future direct > > access to MTRR code. This will not be posted until all of the below > > patches are in and merged. A possible next step here might be to > > consider separating PAT code from MTRR code and making PAT a first > > class citizen, enabling distributions to disable MTRR code in the > > future. I thought this was possible but for some reason I recently > > thought that there was one possible issue to make this happen. I > > suppose we won't know unless we try, unless of course someone already > > knows, Toshi? > > There are two usages on MTRRs: > 1) MTRR entries set by firmware > 2) MTRR entries set by OS drivers > > We can obsolete 2), but we have no control over 1). As UEFI firmwares > also set this up, this usage will continue to stay. So, we should not > get rid of the MTRR code that looks up the MTRR entries, while we have > no need to modify them. > > Such MTRR entries provide safe guard to /dev/mem, which allows > privileged user to access a range that may require UC mapping while > the /dev/mem driver blindly maps it with WB. MTRRs converts WB to UC in > such a case. > > UEFI memory table has memory attribute, which describes cache types > supported in physical memory ranges. However, this information gets > lost when it it is converted to e820 table. Is there no way to modify CPU capability bits upon boot and kick UEFI to re-evaluate ? In such UEFI cases what happens for instance when Xen is used which does not support MTRR? Luis -- 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/