1. A method comprising: enabling access to a plurality of state registers during execution of a guest virtual machine at a data processing device, the plurality of state registers storing state information for the guest virtual machine; responsive to a world switch from execution of the guest virtual machine to execution of a virtual machine manager, preventing virtual machine manager access to the plurality of state registers, and enabling virtual machine manager access to a control block during execution of a virtual machine manager at the data processing device, and storing to the control block only that state information of the plurality of state registers identified as modified during execution of the guest virtual machine, the control block comprising at least one of a plurality of shadow registers corresponding to the plurality of state registers, and a block of a memory coupled to the data processing device; and responsive to a world switch from execution of the virtual machine manager to execution of the guest virtual machine, loading to the plurality of state registers only that state information of the control block identified as modified during execution of the virtual machine manager.