1. In a computing system comprised of a virtualization software layer supporting execution of a virtual machine that includes a guest operating system (OS), a method for executing the virtual machine comprising: converting load and store instructions issued by the guest OS running in a privileged mode into corresponding load and store instructions that execute in a user mode rather than in the privileged mode; marking page tables entries that are accessible by the guest OS as protected, thereby resulting in a trap to the virtualization software layer when a processor of the computing system encounters a load or store instruction that executes in the user mode and corresponds to accessing a marked page table entry; and upon the trap, inspecting at least one validity bit in the marked page table entry to determine whether the marked page table entry includes a mapping of a virtual address reference utilized by a process in the virtual machine to a machine address reference of the computer system.