Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030362AbcCQLNJ (ORCPT ); Thu, 17 Mar 2016 07:13:09 -0400 Received: from smtp.citrix.com ([66.165.176.89]:8543 "EHLO SMTP.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030339AbcCQLNH (ORCPT ); Thu, 17 Mar 2016 07:13:07 -0400 X-IronPort-AV: E=Sophos;i="5.24,349,1454976000"; d="scan'208";a="339850117" Subject: Re: [Xen-devel] MTRR on Xen - BIOS use and implications for Linux To: "Luis R. Rodriguez" , "xen-devel@lists.xensource.com" , Keir Fraser References: CC: Juergen Gross , X86 ML , Toshi Kani , Andrew Cooper , Stuart Hayes , "linux-kernel@vger.kernel.org" , Andy Lutomirski , Borislav Petkov , "H. Peter Anvin" , "Paul McKenney" , Yinghai Lu , "Ingo Molnar" From: David Vrabel Message-ID: <56EA913F.1040403@citrix.com> Date: Thu, 17 Mar 2016 11:13:03 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Icedove/38.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-DLP: MIA1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 697 Lines: 17 tl;dr? Somewhere in here are some actual questions which I will attempt to answer. Please try and be more concise in future. On 16/03/16 20:08, Luis R. Rodriguez wrote: > Toshi noted a while ago as well that if BIOS/firmware enables MTRR but > the kernel does not have it enabled one issue might have been any > MTRRs set up by the BIOS and ensuring the mapping is respected, in > particular UC settings, this concern is raised above. Another issue > though is that the kernel would be "unable to verify if a large page > mapping is aligned with MTRRs" [3] This is not a relevant concern for Xen guests: PV guests do not support superpage mappings and HVM guests never see real MTRRs. David