Hardware support for efficient virtualization

Virtual machines have been used since the 1960’s in creative ways. From multiplexing expensive mainframes to providing backwards compatibility for customers migrating to new hard-ware, virtualization has allowed users to maximize their usage of limited hardware resources. Despite virtual machines falling by the way-side in the 1980’s with the rise of the minicomputer, we are now seeing a revival of virtualization with virtual machines being used for security, isolation, and testing among others. With so many creative uses for virtualization, ensuring high performance for applications running in a virtual machine be-comes critical. In this paper, we survey current research to-wards this end, focusing on the hardware support which en-ables efficient virtualization. Both Intel and AMD have incor-porated explicit support for virtualization into their CPU de-signs. While this can simplify the design of a stand alone virtual machine monitor (VMM), techniques such as paravirtualization and hosted VMM’s are still quite effective in supporting virtual machines. We compare and contrast current approaches to efficient vir-tualization, drawing parallels to techniques developed by IBM over thirty years ago. In addition to virtualizing the CPU, we also examine techniques focused on virtualizing I/O and the memory management unit (MMU). Where relevant, we identify shortcomings in current research and provide our own thoughts on the future direction of the virtualization field.