High vCPU usage on windows 8.1 with GPU Passthrough renders VM unusable and cannot be reached by RDC or console.

As soon as a the GPU is set to passthrough using Xencenter, the whole VM boots but immediately runs at full vcpu usage across the assigned cores, renders the VM unusable as you cannot log in and cannot set which screen to display.

Disabling the gpu allows the VM to boot normally and act normally.

Appreciate that this IS not on the HCL list but probably applies to many configs.