Operating System Virtualization: Practice and Experience

Operating system (OS) virtualization can provide a number of important benefits, including transparent migration of applications, server consolidation, online OS maintenance, and enhanced system security. However, the construction of such a system presents a myriad of traps and pitfalls, even for the most cautious developer, that if overlooked may result in a weak, incomplete virtualization. We present a detailed discussion of key implementation issues in providing OS virtualization in a commodity OS, including system call interposition, virtualization state management, and race conditions. We discuss our experiences in implementing such functionality across two major versions of Linux (2.4 and 2.6) entirely in a loadable kernel module without any kernel modification. We present experimental results on both uniprocessor and multiprocessor systems that demonstrate the ability of our approach to provide fine-grain virtualization with very low overhead