Comment 1 for bug 2052473

is there anything sepcial about the vm you are migrating in terms of what is requested by the flavour.

we have post-copy enabled by default in our downstream OpenStack distribution.

there are some feature that are not supported with it like live migrating a paused VM, and it generally does not work unless you tune some variables in the kernel.

namely you need to set vm.unprivileged_userfaultfd=1 in sysctl

https://github.com/openstack-k8s-operators/edpm-ansible/blob/main/roles/edpm_kernel/vars/main.yml#L105C3-L106

https://github.com/openstack/tripleo-heat-templates/blob/1393d39be367db3acb02508e0e858395a4e4fefa/deployment/nova/nova-compute-container-puppet.yaml#L1631-L1638

if you can provide an example fo the guest XML we may be able to spot any feature that might not be supported although i don't know of any other then pause that would break it. we have a bug for pause
https://bugs.launchpad.net/nova/+bug/1946752

that is fixed back to zed https://review.opendev.org/q/topic:%22bug/1671011%22 but it was only done a month ago so that may not be in a packaged release yet.