upgrade:
  - |
    In the libvirt driver, the default value of the ``<cputune><shares>``
    element has been removed, and is now left to libvirt to decide. This is
    because allowed values are platform dependent, and the previous code was
    not guaranteed to be supported on all platforms. If any of your flavors are
    using the quota:cpu_shares extra spec, you may need to resize to a
    supported value before upgrading.

    To facilitate the transition to no Nova default for ``<cputune><shares>``,
    its value will be removed during live migration unless a value is set in
    the ``quota:cpu_shares`` extra spec. This can cause temporary CPU
    starvation for the live migrated instance if other instances on the
    destination host still have the old default ``<cputune><shares>`` value. To
    fix this, hard reboot, cold migrate, or live migrate the other instances.