Operating System Support for Virtual Machines

A virtual-machine monitor (VMM) is a useful technique for adding functionality below existing operating system and application software. One class of VMMs (called Type II VMMs) builds on the abstractions provided by a host operating system. Type II VMMs are elegant and convenient, but their performance is currently an order of magnitude slower than that achieved when running outside a virtual machine (a standalone system). In this paper, we examine the reasons for this large overhead for Type II VMMs. We find that a few simple extensions to a host operating system can make it a much faster platform for running a VMM. Taking advantage of these extensions reduces virtualization overhead for a Type II VMM to 14-35% overhead, even for workloads that exercise the virtual machine intensively.