Understanding and Leveraging Virtualization Technology in Commodity Computing Systems

Commodity computing platforms are imperfect, requiring various enhancements for performance and security purposes. In the past decade, virtualization technology has emerged as a promising trend for commodity computing platforms, ushering many opportunities to optimize the allocation of hardware resources. However, many abstractions offered by virtualization not only make enhancements more challenging, but also complicate the proper understanding of virtualized systems. The current understanding and analysis of these abstractions are far from being satisfactory. This dissertation aims to tackle this problem from a holistic view, by systematically studying the system behaviors. The focus of our work lies in performance implication and security vulnerabilities of a virtualized system.;We start with the first abstraction---an intensive memory multiplexing for I/O of Virtual Machines (VMs)---and present a new technique, called Batmem, to effectively reduce the memory multiplexing overhead of VMs and emulated devices by optimizing the operations of the conventional emulated Memory Mapped I/O in hypervisors. Then we analyze another particular abstraction---a nested file system---and attempt to both quantify and understand the crucial aspects of performance in a variety of settings. Our investigation demonstrates that the choice of a file system at both the guest and hypervisor levels has significant impact upon I/O performance.;Finally, leveraging utilities to manage VM disk images, we present a new patch management framework, called Shadow Patching, to achieve effective software updates. This framework allows system administrators to still take the offline patching approach but retain most of the benefits of live patching by using commonly available virtualization techniques. to demonstrate the effectiveness of the approach, we conduct a series of experiments applying a wide variety of software patches. Our results show that our framework incurs only small overhead in running systems, but can significantly reduce maintenance window