From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: [PATCH 3/4 V3] X86: MPX IA32_BNDCFGS msr handle Date: Wed, 27 Nov 2013 14:51:16 +0000 Message-ID: <529606E4.5000003@citrix.com> References: <5295FA3B.8080602@citrix.com> <52960227.9080701@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: "Liu, Jinsong" Cc: "xen-devel@lists.xen.org" , "keir@xen.org" , "haoxudong.hao@gmail.com" , Jan Beulich , "Ian.Campbell@citrix.com" List-Id: xen-devel@lists.xenproject.org On 27/11/13 14:37, Liu, Jinsong wrote: > Andrew Cooper wrote: >> On 27/11/13 14:27, Liu, Jinsong wrote: >>> Andrew Cooper wrote: >>>> On 27/11/13 13:50, Liu, Jinsong wrote: >>>>> From 291adaf4ad6174c5641a7239c1801373e92e9975 Mon Sep 17 00:00:00 >>>>> 2001 From: Liu Jinsong >>>>> Date: Thu, 28 Nov 2013 05:26:06 +0800 >>>>> Subject: [PATCH 3/4 V3] X86: MPX IA32_BNDCFGS msr handle >>>>> >>>>> When MPX supported, a new guest-state field for IA32_BNDCFGS >>>>> is added to the VMCS. In addition, two new controls are added: >>>>> - a VM-exit control called "clear BNDCFGS" >>>>> - a VM-entry control called "load BNDCFGS." >>>>> VM exits always save IA32_BNDCFGS into BNDCFGS field of VMCS. >>>>> >>>>> Signed-off-by: Xudong Hao >>>>> Reviewed-by: Liu Jinsong >>>>> >>>>> Unlikely, but in case VMX support is not available, not expose >>>>> MPX to hvm guest. >>>> You are still missing the point. >>>> >>>> I as the administrator choose to prevent an HVM guest from using >>>> MPX. Perhaps I want to create a heterogeneous pool. >>>> >>>> Therefore, the bit is disabled in the domains cpuid policy, despite >>>> being available on the hardware. >>>> >>>> ~Andrew >>>> >>> Could you tell me the reason why choose to prevent HVM from using >>> MPX? >>> >>> Thanks, >>> Jinsong >> For exactly the case I gave - a VM in a heterogeneous pool where one >> server supports MPX and the other is lacking the MPX feature. >> >> ~Andrew >> > I didn't see the point of your case to prevent HVM MPX feature. > Could you elaborate more of your concern? > > Thanks, > Jinsong It is very common to have pools of servers made of different generations of CPU. E.g. Ivy Bridge and Haswell. To safely migrate a VM, the feature set the VM can see must be the common subset of the two. ~Andrew