Patent ID: 8316374

Claim:
A method for replacing a first hypervisor on a computer system with a second hypervisor, each hypervisor comprising virtualization software that is logically interposed and interfacing between one or more virtual machines (VMs) and hardware resources of a hardware platform, the virtualization software causing the one or more VMs to execute concurrently with one another and the virtualization software, the method comprising: without significant interruption of execution of any of the one or more VMs, hot-removing a first portion of the hardware resources from control by the first hypervisor, the hardware resources including CPU resources, memory resources, and I/O resources, the CPU resources including one or more CPUs, the memory resources including system memory, and the I/O resources including one or more I/O devices, the first portion of the CPU resources being sufficient to support execution of the second hypervisor; without significant interruption of execution of any of the one or more VMs, starting execution of the second hypervisor using the first portion of the hardware resources, the first and second hypervisors thereafter executing concurrently on the same hardware platform, the hot-removing of the first portion of the hardware resources and the starting of the execution of the second hypervisor comprising migrating ownership and control of the first portion of the hardware resources from the first hypervisor to the second hypervisor and modifying a hardware resource scheduling algorithm of the first hypervisor causing the first hypervisor to stop using the first portion of the hardware resources; separately migrating a plurality of additional portions of the hardware resources from the first hypervisor to the second hypervisor, at least one of the additional portions of the hardware resources including memory pages allocated to one of the one or more VMs, the separately migrating of the additional portions of the hardware resources comprising transferring ownership and control of the additional portions of the hardware resources from the first hypervisor to the second hypervisor, the separately migrating of the plurality of additional portions of the hardware resources continuing until all of the one or more VMs are migrated to the second hypervisor; migrating any remaining portions of the hardware resources under control of the first hypervisor to a control of the second hypervisor, causing the first hypervisor to inform device drivers to stop using the hardware resources previously controlled by the first hypervisor; and shutting down the first hypervisor.