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 physical core enabled to operate in a single thread (ST) mode and a multithreading (MT) mode, wherein the single physical core includes multiple physical threads, and wherein the machine is 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 single physical core, wherein the guest entity includes all or a part of a guest VM, and wherein the issuing of the start-VE instruction is performed by a host running on one of the multiple physical threads on the single physical core in the ST mode; and executing the start-VE instruction by the machine, wherein the executing of the start-VE instruction by the machine comprises: mapping each of the multiple logical threads to a corresponding one of the multiple physical threads; initializing each of the multiple mapped physical threads with a state of a corresponding logical thread; and starting execution of the guest entity on the single physical core in the MT mode.