1. A method, comprising: detecting, by a hypervisor being executed by a processing device of a host computer system, a transition to a first execution mode by a guest operating system (OS) running on the host computer system, wherein the first execution mode is characterized by at least one of: a first physical address size or a first general purpose register size; and responsive to detecting the transition to the first execution mode, enabling a virtual machine (VM) function to be executed by the guest OS in the first execution mode.