Comment 8 for bug 1944619

this is where we detach the interfaces

https://github.com/openstack/nova/blob/66574018b517f14dc26e581d0ddaa7788806f83e/nova/virt/libvirt/driver.py#L9602-L9625

in _live_migration_operation then we start the migration here
https://github.com/openstack/nova/blob/66574018b517f14dc26e581d0ddaa7788806f83e/nova/virt/libvirt/driver.py#L9662-L9667

in _rollback_live_migration we do correctly revert the pci allcoations
https://github.com/openstack/nova/blob/master/nova/compute/manager.py#L9083-L9093

and we call back into the driver to its revert

https://github.com/openstack/nova/blob/master/nova/compute/manager.py#L9115-L9116

and that reattached the interface to the vms
https://github.com/openstack/nova/blob/66574018b517f14dc26e581d0ddaa7788806f83e/nova/virt/libvirt/driver.py#L10127-L10137

unless you have correctly configured network manager in the guest to retrigger on the hotplug of the interface the guest wont have network connectivty restored until it reboots and the on boot network configurtion scripts run.

we have specifcaly catered for this rollback case in the code
https://github.com/openstack/nova/blob/66574018b517f14dc26e581d0ddaa7788806f83e/nova/virt/libvirt/driver.py#L10110-L10125
so i am not seeing anythign that woudl point to a nova bug currently.

the libvirt error simply looks like you had instance that were affected by https://bugs.launchpad.net/nova/+bug/1851545 which will only be noticed if you try to start new instance on host ver the vms are not using the pci device that is claimed in the database.