Proposed libvirt package on Focal system with original unmodified kernel and driver:
$ uname -a
Linux node-laveran 5.4.0-81-generic #91-Ubuntu SMP Thu Jul 15 19:09:17 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

$ cat /sys/class/net/enp129s0f0/device/driver/module/version
5.0-0

$ lspci -nnvv | grep Mellanox
03:00.0 Ethernet controller [0200]: Mellanox Technologies MT27800 Family [ConnectX-5] [15b3:1017]
        Subsystem: Mellanox Technologies MT27800 Family [ConnectX-5] [15b3:0061]
03:00.1 Ethernet controller [0200]: Mellanox Technologies MT27800 Family [ConnectX-5] [15b3:1017]
        Subsystem: Mellanox Technologies MT27800 Family [ConnectX-5] [15b3:0061]
03:00.2 Ethernet controller [0200]: Mellanox Technologies MT27800 Family [ConnectX-5 Virtual Function] [15b3:1018]
        Subsystem: Mellanox Technologies MT27800 Family [ConnectX-5 Virtual Function] [15b3:0061]
...

# Note that in addition to libvirt from -proposed the system has a test
# package for the in-flight os-vif changes installed.
$ dpkg -l |grep libvirt
ii  libvirt-clients                      6.0.0-0ubuntu8.13                                    amd64        Programs for the libvirt library
ii  libvirt-daemon                       6.0.0-0ubuntu8.13                                    amd64        Virtualization daemon
ii  libvirt-daemon-driver-qemu           6.0.0-0ubuntu8.13                                    amd64        Virtualization daemon QEMU connection driver
ii  libvirt-daemon-driver-storage-rbd    6.0.0-0ubuntu8.13                                    amd64        Virtualization daemon RBD storage driver
ii  libvirt-daemon-system                6.0.0-0ubuntu8.13                                    amd64        Libvirt daemon configuration files
ii  libvirt-daemon-system-systemd        6.0.0-0ubuntu8.13                                    amd64        Libvirt daemon configuration files (systemd)
ii  libvirt0:amd64                       6.0.0-0ubuntu8.13                                    amd64        library for interfacing with different virtualization systems

$ sudo grep -A6 hostdev /etc/libvirt/qemu/instance-00000001.xml
    <interface type='hostdev' managed='yes'>
      <mac address='fa:16:3e:1a:59:22'/>
      <source>
        <address type='pci' domain='0x0000' bus='0x03' slot='0x0b' function='0x4'/>
      </source>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>

$ openstack server list --long
...
| c575e200-74cf-45bd-801e-712d3405f460 | fnord-node-laveran-1 | ACTIVE | None       | Running     | network=10.42.2.217                | ubuntu     | d9aa89af-9ad7-4770-83ba-194f03fec7dc | m1.large    | 96afbb8a-697f-4de8-aa76-b8604bc01180 | nova              | node-laveran.maas |            |
...

$ ssh -i id_rsa fnord-node-laveran-1 lspci
...
00:03.0 Ethernet controller: Mellanox Technologies MT27800 Family [ConnectX-5 Virtual Function]
...

<install OFED drivers, reboot and restart instances>

$ uname -a
Linux node-laveran 5.4.0-81-generic #91-Ubuntu SMP Thu Jul 15 19:09:17 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

$ cat /sys/class/net/enp129s0f0/device/driver/module/version
5.4-1.0.3

$ ssh -i id_rsa fnord-node-laveran-1 lspci
...
00:03.0 Ethernet controller: Mellanox Technologies MT27800 Family [ConnectX-5 Virtual Function]
...