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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,

  • hardware emulation via /dev/kvm will not be attempted. qemu will be used for software emulation instead.
  • in-kernel virtio-net backend emulation via /dev/vhost-net will not be attempted. QEMU userland virtio NIC emulation will be used for virtio-net interface instead.

Configuration

Enabling software emulation is a cluster-wide setting, and is activated using a ConfigMap in the kubevirt namespace. It can be enabled with the following command:

cluster/kubectl.sh --namespace kubevirt create configmap kubevirt-config \
    --from-literal debug.useEmulation=true

If the kubevirt/kubevirt-config ConfigMap already exists, the above entry can be added using:

cluster/kubectl.sh --namespace kubevirt edit configmap kubevirt-config

In this case, add the debug.useEmulation: "true" setting to data:

apiVersion: v1
kind: ConfigMap
metadata:
  name: kubevirt-config
  namespace: kubevirt
data:
  debug.useEmulation: "true"

NOTE: The values of ConfigMap.data are strings. Yaml requires the use of quotes around "true" to distinguish the value from a boolean.