We released a new hotfix for Hyper-V today.

This hotfix addresses an issue where virtual machines may crash (with a STOP 0×000000D1, DRIVER_IRQL_NOT_LESS_OR_EQUAL error) when it is being live migrated.  While this problem is relatively hard to encounter – I would encourage anyone who is using live migration to plan to deploy this hotfix in the near future, as you do not want to hit this accidentally.

You can download this fix directly from here: http://support.microsoft.com/kb/2636573

Alternatively, it is also being distributed through Windows Update.  Unfortunately it is only available as an optional update though – so you will need to explicitly select to install it on your servers. 

Either way, this hotfix does require that you reboot the physical server so you will need to plan the deployment of the fix appropriately for your environment.

Cheers,
Ben