Re: [Xen-devel] vMCE vs migration

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 26.01.12 at 17:54, George Dunlap <george.dunlap@xxxxxxxxxx> wrote:
> On Tue, 2012-01-24 at 11:08 +0000, Jan Beulich wrote:
>> >>> On 24.01.12 at 11:29, George Dunlap <George.Dunlap@xxxxxxxxxxxxx> wrote:
>> > On Mon, Jan 23, 2012 at 11:08 AM, Jan Beulich <JBeulich@xxxxxxxx> 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?

Would certainly be desirable to get fixed.

> Are you going to put it on your to-do list? :-)

I'll first check with Intel whether the engineers who wrote that code
could make an attempt.

Jan


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