I/o paravirtualization at the device file boundary

Abstract

Paravirtualization is an important I/O virtualization technology since it uniquely provides all of the following benefits: the ability to share the device between multiple VMs, support for legacy devices without virtualization hardware, and high performance. However, existing paravirtualization solutions have one main limitation: they only support one I/O device class, and would require significant engineering effort to support new device classes and features. In this paper, we present Paradice, a solution that vastly simplifies I/O paravirtualization by using a common paravirtualization boundary for various I/O device classes: Unix device files. Using this boundary, the paravirtual drivers simply act as a class-agnostic indirection layer between the application and the actual device driver. We address two fundamental challenges: supporting cross-VM driver memory operations without changes to applications or device drivers and providing fault and device data isolation between guest VMs despite device driver bugs. We implement Paradice for x86, the Xen hypervisor, and the Linux and FreeBSD OSes. Our implementation paravirtualizes various GPUs, input devices, cameras, an audio device, and an Ethernet card for the netmap framework with ~7700 LoC, of which only ~900 are device class-specific. Our measurements show that Paradice achieves performance close to native for different devices and applications including netmap, 3D HD games, and OpenCL applications.