Enable Hyper-V Windows 2012 will uses only one Dual CPU from two

Hello,

i have a Server with two Dual Intel XEON CPU. When enable the Hyper-V role then the Server works only with one CPU. The device Manager says there are 4 CPU but the Task Manager Shows only 2. I know the both CPU are the same model, but the stepping is different. When Hyper is disabled then it works correct with the 2 Dual CPU and the Taskmanager Show 4.

Can anybody help me.