Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758149AbcC2VW3 (ORCPT ); Tue, 29 Mar 2016 17:22:29 -0400 Received: from g4t3425.houston.hp.com ([15.201.208.53]:14153 "EHLO g4t3425.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754422AbcC2VW2 (ORCPT ); Tue, 29 Mar 2016 17:22:28 -0400 Message-ID: <1459289681.6393.714.camel@hpe.com> Subject: Re: [Xen-devel] MTRR on Xen - BIOS use and implications for Linux From: Toshi Kani To: "Luis R. Rodriguez" , David Vrabel , Toshi Kani Cc: "xen-devel@lists.xensource.com" , Keir Fraser , Juergen Gross , X86 ML , Andrew Cooper , Stuart Hayes , "linux-kernel@vger.kernel.org" , Andy Lutomirski , Borislav Petkov , "H. Peter Anvin" , Paul McKenney , Yinghai Lu , Ingo Molnar , Prarit Bhargava Date: Tue, 29 Mar 2016 16:14:41 -0600 In-Reply-To: References: <56EA913F.1040403@citrix.com> <20160317185647.GR1990@wotan.suse.de> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.18.4 (3.18.4-1.fc23) Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1436 Lines: 31 On Tue, 2016-03-29 at 10:22 -0700, Luis R. Rodriguez wrote: > On Thu, Mar 17, 2016 at 11:56 AM, Luis R. Rodriguez > wrote: > > On Thu, Mar 17, 2016 at 11:13:03AM +0000, David Vrabel wrote: > > > 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, > > To be clear the requirement expressed here was needing at least to > implement get_mtrr() on the Linux Xen guest side, it'd call the > already implemented hypercall XENPF_read_memtype in turn. Toshi had > hinted this was perhaps needed on the Linux Xen guest side given that > the BIOS may have set up MTRRs on its own, so we needed the guest to > be able to get the right type for a particular range. More on that > below No, I did not say that. :-)  I said it because you mentioned that you wanted to disable MTRRs even though BIOS enabled MTRRs. My point is that the kernel should not change the MTRR setup.  That is:  - If BIOS enables MTRRs, then kernel needs to keep them enabled.  - If BIOS disables MTRRs, then the kernel needs to keep them disabled. Therefore, the kernel can keep MTRRs disabled on Xen guests. I think you repeated the same questions in this email, so please refer my previous reply for the rest. Thanks, -Toshi