From mboxrd@z Thu Jan 1 00:00:00 1970 From: George Dunlap Subject: Re: vMCE vs migration Date: Thu, 26 Jan 2012 16:54:56 +0000 Message-ID: <1327596896.24345.66.camel@elijah> References: <4F1D4DCD020000780006E593@nat28.tlf.novell.com> <4F1E9F45020000780006EA5E@nat28.tlf.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4F1E9F45020000780006EA5E@nat28.tlf.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Jan Beulich Cc: George Dunlap , "xen-devel@lists.xensource.com" , Ian Campbell List-Id: xen-devel@lists.xenproject.org On Tue, 2012-01-24 at 11:08 +0000, Jan Beulich wrote: > >>> On 24.01.12 at 11:29, George Dunlap wrote: > > On Mon, Jan 23, 2012 at 11:08 AM, Jan Beulich wrote: > >> x86's vMCE implementation lets a guest know of as many MCE reporting > >> banks as there are in the host. While a PV guest could be expected to > >> deal with this number changing (particularly decreasing) during migration > >> (not currently handled anywhere afaict), for HVM guests this is certainly > >> wrong. > >> > >> At least to me it isn't, however, clear how to properly handle this. The > >> easiest would appear to be to save and restore the number of banks > >> the guest was made believe it can access, making vmce_{rd,wr}msr() > >> silently tolerate accesses between the host and guest values. > > > > We ran into this in the XS 6.0 release as well. I think that the > > ideal thing to do would be to have a parameter that can be set at > > boot, to say how many vMCE banks a guest has, defaulting to the number > > of MCE banks on the host. This parameter would be preserved across > > migration. Ideally, a pool-aware toolstack like xapi would then set > > this value to be the value of the host in the pool with the largest > > number of banks, allowing a guest to access all the banks on any host > > to which it migrates. > > > > What do you think? > > That sounds like the way to go. So should we put this on IanC's to-do-be-done list? Are you going to put it on your to-do list? :-) -George