Have 2 Dell R900 ( Intel x7350 ) and 4 Dell R720 ( Intel E5-2650-V2) hosts. Tried to migrate VM's off of R900's ( get errors KB1003212, KB 1034926 ) so that won't work. Have checked settings and BIOS (2.2.2 and 2.2.3 on R720's and all looks ok. Assume the only way to get off R900's is to shutdown VM's and cold migrate them and then restart them on the new hosts. Is there anything else I should try first??
The CPU feature set is assigned to a VM when it is powered on. So if there's a feature available at this time that's not available on a target host, you unfortunately need to shut down the VM in order to be able to migrate it.
You should double check the CPU families for EVC Compatibility on the Matrix
Also as stated, the CPU features are set when the CPU powers on so if you enable EVC when the VMs are on you will need to shut them down, not a reboot shutdown and power on via the vSphere Client, so they create new world objects. This will all the VMs to pickup the new masking from the EVC configuration.