NestCloud: Towards practical nested virtualization

This paper describes a nested virtualization solution, which allows virtual machine monitor (VMM) with virtual machine to run within another virtual machine with low overhead. Previous nested virtualization solutions on x86 platform are mainly based on emulation, which result in poor performance and poor usability. We propose and implement NestCloud, a practical high performance nested virtualization architecture, which fully employs the hardware virtualization extensions. Furthermore, three optimizations are provided to reduce the overhead of nested guests: (1) Guest Page Fault Bypassing, which permits nested guests to handle page faults without VM Exit; (2) Virtual EPT (Extended Page Table), which eliminates unnecessary page faults introduced by shadow page table in nested VMM; (3) PV VMCS, which provides more effective VMCS accessing for nested VMM. Experimental results show that the performance of NestCloud guest is close to single level guest in both CPU-intensive and memory-intensive benchmarks. The CPU overhead is 5.22% and the memory overhead is 5.69%, which makes the nested guest of NestCloud comparable with a conventional one.