EXO: Accelerating Storage Paravirtualization with eBPF

KVM is the dominant VM hypervisor on Linux, and relies on QEMU to realize the backends of the virtio family of devices such as virtio-blk. However, KVM/QEMU-based paravirtualization prolongs the guest I/O path with multiple context switches. As fast NVMe storage devices have been widely used, the software overhead is becomes non-negligible. This paper presents EXO, an extension of virtio-blk for efficient KVM/QEMU-based storage paravirtualization. The insight is that no matter how complex the QEMU backend’ processing is, to handle a guest I/O request, the host storage stack only needs to know the request’s guest-to-host address mapping. Therefore, we preserve the original slow I/O path of virtio-blk as a fallback, and leverage eBPF to introduce an in-kernel fast path that directly queries the address mapping without switching to the user-space backend processing. Extensive evaluation shows that compared to existing storage paravirtualization solutions, EXO achieves similar or even higher performance.