Making a virtual machine monitor interruptible

This paper describes our approach to making the Gandalf Virtual Machine Monitor (VMM) interruptible. Gandalf is designed to be a lightweight VMM for use in embedded systems. Hardware interrupts are directly notified to its guest operating system (OS) kernel without the interventions of the VMM, and the VMM only processes the exceptions caused by the guest kernel. Since the VMM processes those exceptions with interrupts disabled, the detailed performance analysis using PMC (Performance Monitoring Counters) revealed that the time duration while the interrupts are disabled is rather long. By making Gandalf interruptible, we are able to make VMM based systems more suitable for embedded systems. We analyzed the requirements for making Gandalf interruptible, and designed and implemented mechanisms to achieve this. The experimental results show that making Gandalf interruptible significantly reduces a duration of execution time with interrupts disabled while it does not impact performance.