kvm-info-nfd-plugin is an addon toolset for the kubernetes node feature discovery. It plugs in the user-specific features support, and add labels to the hosts to report if they support KVM HyperV enlightenments.

This is useful for kubevirt, which can use these labels to safely and efficiently schedule VMs on hyoerv-capable hosts.

Checking KVM support in kernels is hard. In general, things are supposed to just work, but bugs, backports and various issues may result in some kernel versions not work properly.

This project don't aim to perfectly represent the state of the Hyper-V support. That would be impractical. Instead, this project aim to provide a corse-grained labelling to whitelist or blacklist some kernel versions.

We believe this is a good compromise between maintenability and user experience.

The toolset features few NFD-compatible plugins:

• kvm-caps-info-nfd-plugin
• kvm-version-info-nfd-plugin

You can install all the plugins together, and they are supposed to coexist without issue (otherwise please report a bug), but you most likely want to install just either one.

Unless you know what are you doing, we recommend to install and run only kvm-caps-info-nfd-plugin, which add the labels that kubevirt >= 0.16.0 expects when it is configured to run with strict HyperV check. Please see the kubevirt documentation.

This plugin exposes per-feature, granular labels, for each feature exposed by libvirt >= 5.1 Example output

/kvm-info-cap-hyperv-base
/kvm-info-cap-hyperv-time
/kvm-info-cap-hyperv-vpindex
/kvm-info-cap-hyperv-tlbflush
/kvm-info-cap-hyperv-ipi
/kvm-info-cap-hyperv-synic
/kvm-info-cap-hyperv-synic2
/kvm-info-cap-hyperv-frequencies
/kvm-info-cap-hyperv-reset
/kvm-info-cap-hyperv-runtime
/kvm-info-cap-hyperv-synictimer
/kvm-info-cap-hyperv-reenlightenment

Using this plugin, KubeVirt >= 0.16.0 can do informed scheduled decisions on a per-feature basis.

QEMU exposes quite a lot of hyperv enlightenments. We choose to not expose all of them, to avoid a combinatorial explosion in the check matrix. Thus, kvm-info-nfd-plugin just exports two set of labels:

• hyperv: signals that the host is whitelisted, thus has no known gotchas, thus any enlightenment can be safely turned on
• hyperv-lev2: same as above but for L2 (nested hyperv) enlightenments. These are separated because enabling L2 enlightenments without running nested virtualization may cause a small performance loss.

To run the testsuite:

make tests

• add more functional tests