From mboxrd@z Thu Jan 1 00:00:00 1970 From: George Dunlap Subject: Re: PVH and mtrr/PAT......... Date: Fri, 22 Nov 2013 12:16:42 +0000 Message-ID: <528F4B2A.1010109@eu.citrix.com> References: <20131119181139.5e794708@mantra.us.oracle.com> <528C83F00200007800104DB6@nat28.tlf.novell.com> <20131120142450.537a3a3d@mantra.us.oracle.com> <20131121154139.584a6d4a@mantra.us.oracle.com> <528F353D.4090004@eu.citrix.com> <528F496F0200007800105BFF@nat28.tlf.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta3.messagelabs.com ([195.245.230.39]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1VjpfQ-0006d8-Tb for xen-devel@lists.xenproject.org; Fri, 22 Nov 2013 12:17:01 +0000 In-Reply-To: <528F496F0200007800105BFF@nat28.tlf.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Jan Beulich Cc: xen-devel , Eddie Dong , Jun Nakajima , Tim Deegan List-Id: xen-devel@lists.xenproject.org On 22/11/13 11:09, Jan Beulich wrote: >>>> On 22.11.13 at 11:43, George Dunlap wrote: >> I'm not incredibly familiar with the PAT / MTRR stuff, either from a >> hardware level or a Xen level, so sorry if this is a dumb question. It >> sounds like you're saying, because we have virtual MTRRs that are >> already translated into EPT types, we should disable virtual MTRRs and >> use PAT instead. That doesn't make any kind of sense to me. (I didn't >> understand it when Jan said it either.) > The underlying observation is that MTRRs aren't really needed - > all they can do can be done with PAT. They pre-date PAT though, > hence hardware vendors can't easily drop them. But in a model > like PVH I just don't see the value of allowing their use, considering > that this adds unnecessary complexity. OK -- so when we move forward with the plan of "PVH mode is HVM mode with a couple of tweaks", you think that we should have an "enable virtual MTRR" flag, and disable this for PVH mode? -George