IXIV VMM: A VMM on 2-Level Ring Architecture

Software defects in embedded systems becomes an especially serious issue as their increased software complexity makes it difficult to throughly validate and guarantee their correctness. One of the solutions to deal with such an issue at runtime is to exploit a virtual machine monitor (VMM). While most of the currently available VMMs are constructed to run on complex CPUs, no well-known VMM runs on embedded CPUs. This is because most embedded CPUs provide only 2-level protection rings that are not sufficient to accommodate a VMM along with an operating system (OS) kernel and its user processes. This paper proposes a method to support VMMs on processor architectures with the limited number of protection rings. We implemented a VMM by using the proposed method, and successfully execute Linux as a guest OS on it. The evaluation results show the performance of the guest Linux on the VMM is reasonably efficient.