An Open-Source ARM Virtualization System

As ARM CPUs become increasingly common in mobile devices and servers, there is a growing demand for providing the benefits of virtualization for ARM-based devices. We present our experiences building the Linux ARM hypervisor, KVM/ARM, the first full system ARM virtualization solution that can run unmodified guest operating systems on ARM multicore hardware. KVM/ARM introduces split-mode virtualization, allowing a hypervisor to split its execution across CPU modes and be integrated into the Linux kernel. This allows KVM/ARM to leverage existing Linux hardware support and functionality to simplify hypervisor development and maintainability while utilizing recent ARM hardware virtualization extensions to run virtual machines with comparable performance to native execution. KVM/ARM has been successfully merged into the mainline Linux kernel, ensuring that it will gain wide adoption as the virtualization platform of choice for ARM. We provide the first measurements on real hardware of a complete hypervisor using ARM hardware virtualization support. Our results demonstrate that KVM/ARM has modest virtualization performance and power costs, and can achieve lower performance and power costs compared to x86-based Linux virtualization on multicore hardware.

Smartphones are increasingly ubiquitous, and many users carry multiple phones to accommodate work, personal, and geographic mobility needs. We present Cells, a virtualization architecture for enabling multiple virtual smartphones to run simultaneously on the same physical cellphone in an isolated, secure manner. Cells introduces a usage model of having one foreground virtual phone and multiple background virtual phones. This model enables a new device namespace mechanism and novel device proxies that integrate with lightweight operating system virtualization to multiplex phone hardware across multiple virtual phones while providing native hardware device performance. Cells virtual phone features include fully accelerated 3D graphics, complete power management features, and full telephony functionality with separately assignable telephone numbers and caller ID support. We have implemented a prototype of Cells that supports multiple Android virtual phones on the same phone. Our performance results demonstrate that Cells imposes only modest runtime and memory overhead, works seamlessly across multiple hardware devices including Google Nexus 1 and Nexus S phones, and transparently runs Android applications at native speed without any modifications.

As ARM CPUs grow in performance and ubiquity across phones, netbooks, and embedded computers, providing virtualization support for ARM-based devices is increasingly important. We present KVM/ARM, a KVM-based virtualization solution for ARM-based devices that can run virtual machines with nearly unmodified operating systems. Because ARM is not virtualizable, KVM/ARM uses lightweight paravirtualization, a script-based method to automatically modify the source code of an operating system kernel to allow it to run in a virtual machine. Lightweight paravirtualization is architecture specific, but operating system independent. It is minimally intrusive, completely automated, and requires no knowledge or understanding of the guest operating system kernel code. By leveraging KVM, which is an intrinsic part of the Linux kernel, KVM/ARM’s code base can be always kept in line with new kernel releases without additional maintenance costs, and can be easily included in most Linux distributions. We have implemented a KVM/ARM prototype based on the Linux kernel used in Google Android, and demonstrated its ability to successfully run nearly unmodified Linux guest operating systems.