1. A method comprising: with a hypervisor, detecting that a guest system has executed a memory monitor command for a virtual processor; making a copy of data that is stored at a guest memory address associated with the memory monitor command; storing the copy at a hypervisor memory address; with the hypervisor, in response to detecting that the guest system has executed a wait command, executing a loop until the copy is different than the data stored in the guest memory address; and within the loop, causing the virtual processor to enter a halt state for a predetermined period of time.