A processing core comprising instruction execution logic circuitry and register space. The register space to be loaded from a VMCS, commensurate with a VM entry, with information indicating whether a service provided by the processing core on behalf of the VMM is enabled. The instruction execution logic to, in response to guest software invoking an instruction: refer to the register space to confirm that the service has been enabled, and, refer to second register space or memory space to fetch input parameters for said service written by said guest software.