ARMvisor: System Virtualization for ARM

In recent years, system virtualization technology has gradually shifted its focus from data centers to embed-ded systems for enhancing security, simplifying the pro-cess of application porting as well as increasing sys-tem robustness and reliability. In traditional servers, which are mostly based on x86 or PowerPC processors, Kernel-based Virtual Machine (KVM) is a commonly adopted virtual machine monitor. However, there are no such KVM implementations available for the ARM ar-chitecture which dominates modern embedded systems. In order to understand the challenges of system virtual-ization for embedded systems, we have implemented a hypervisor, called ARMvisor, which is based on KVM for the ARM architecture. In a typical hypervisor, there are three major compo-nents: CPU virtualization, memory virtualization, and I/O virtualization. For CPU virtualization, ARMvisor uses traditional “trap and emulate ” to deal with sensi-tive instructions. Since there is no hardware support for virtualization in ARM architecture V6 and earlier, we have to patch the guest OS to force critical instruc-tions to trap. For memory virtualization, the functional-ity of the MMU, which translates a guest virtual address to host physical address, is emulated. In ARMvisor, a shadow page table is dynamically allocated to avoid the inefficiency and inflexibility of static allocation for the guest OSes. In addition, ARMvisor uses R-Map to take care of protecting the memory space of the guest OS. For I/O virtualization, ARMvisor relies on QEMU to emulate I/O devices. We have implemented KVM on ARM-based Linux kernel for all three components in ARMvisor. At this time, we can successfully run a guest Ubuntu system on an Ubuntu host OS with ARMvisor on the ARM-based TI BeagleBoard.