vhostnet

vhost_net is a Linux kernel module that provides the vhost backend for virtio-net devices used by KVM and QEMU virtualization. It accelerates the virtual network data path by handling virtio-net protocol processing in the host kernel rather than in the QEMU process, reducing user-kernel context switches and data copying and typically improving throughput and latency for virtual machines.

Operation and scope: When a VM exposes a virtio-net device, the host can connect it to the vhost_net backend. The kernel-side vhost_net processes the virtio rings and forwards traffic to the host networking stack, usually via the host’s bridge or TAP-based networking setup. This pathway allows guest traffic to traverse the host’s network interfaces with lower overhead than a fully user-space path.

System integration: vhost_net is part of the mainline Linux kernel and is used automatically by modern virtualization stacks when available and enabled. It can be loaded or unloaded via standard kernel module tools. It is designed to work alongside other vhost backends (such as vhost-blk and vhost-user) and with common host-networking configurations, including bridges and macvtap devices.

Performance and considerations: In supported configurations, vhost_net provides measurable performance benefits, including higher throughput and reduced CPU usage. It preserves the abstract virtio-net interface for the guest, while changing only the data path in the host. Potential considerations include compatibility with certain host networking layouts or features, and, as with any kernel-space component, standard security and stability considerations apply.

See also: virtio, vhost, vhost-user, KVM, QEMU, vhost-blk.