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software-emulation.md

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Software Emulation

By default KubeVirt uses the /dev/kvm device to enable hardware emulation. This is almost always desirable, however there are a few exceptions where this approach is problematic. For instance, running KubeVirt on a cluster where the nodes do not support hardware emulation. In the same way, by default KubeVirt requires presence of /dev/vhost-net in case that at least one network interface model is virtio (note: if the NIC model is not explicitly specified, by default virtio is chosen).

If useEmulation is enabled,

  • qemu will be used for software emulation, in case that hardware emulation via /dev/kvm is unavailable.
  • QEMU userland virtio NIC emulation will be used for virtio-net interfaces, in case that in-kernel virtio-net backend emulation via /dev/vhost-net is unavailable.

If useEmulation is disabled, and a required hardware emulation device is unavailable (/dev/kvm, or /dev/vhost-net for a VirtualMachine which uses virtio for at least one interface), the VirtualMachine will fail to start and an error will be reported.

Note that software emulation, when enabled, is only used as a fallback when hardware emulation is not available. Hardware emulation is always attempted first, regardless of the value of the useEmulation.

Configuration

Enabling software emulation is a cluster-wide setting, and is activated by editing the KubeVirt CR as follows:

kubevirtci/cluster-up/kubectl.sh --namespace kubevirt edit kubevirt kubevirt

Add the following snippet to the spec:

spec:
  configuration:
    developerConfiguration:
      useEmulation: true