1. A computer system for dispatching a multithreaded guest virtual machine (VM), the computer system comprising: a configuration comprising a machine that includes a single core enabled to operate in a single thread (ST) mode and a multithreading (MT) mode, the core including physical threads; the machine configured to perform a method comprising: issuing a start-virtual-execution (start-VE) instruction to dispatch a guest entity comprising multiple logical threads on the core, the guest entity including all or a part of a guest VM, and the issuing by a host running on one of the physical threads on the core in the ST mode, the executing of the start-VE instruction by the machine comprising: mapping each of the logical threads to a corresponding one of the physical threads; initializing each of the mapped physical threads with a state of the corresponding logical thread; and starting execution of the guest entity on the core in MT mode.