Re: [Xen-devel] vMCE vs migration

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

Jan


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