Comment 12 for bug 1809083

First I verified the test setup with 16.04 / 18.04 as is.
I did hit the expected error:
2019-02-25T14:47:41.407008Z qemu-system-ppc64: error while loading state for instance 0x0 of device 'cpu'
2019-02-25T14:47:41.407312Z qemu-system-ppc64: load of migration failed: Invalid argument

Then I upgraded to -proposed

$ sudo apt install qemu-kvm/bionic-proposed qemu-block-extra/bionic-proposed qemu-system-common/bionic-proposed qemu-system-ppc/bionic-proposed qemu-utils/bionic-proposed
Reading package lists... Done
Building dependency tree
Reading state information... Done
Selected version '1:2.11+dfsg-1ubuntu7.10' (Ubuntu:18.04/bionic-proposed [ppc64el]) for 'qemu-kvm'
Selected version '1:2.11+dfsg-1ubuntu7.10' (Ubuntu:18.04/bionic-proposed [ppc64el]) for 'qemu-block-extra'
Selected version '1:2.11+dfsg-1ubuntu7.10' (Ubuntu:18.04/bionic-proposed [ppc64el]) for 'qemu-system-common'
Selected version '1:2.11+dfsg-1ubuntu7.10' (Ubuntu:18.04/bionic-proposed [ppc64el]) for 'qemu-system-ppc'
Selected version '1:2.11+dfsg-1ubuntu7.10' (Ubuntu:18.04/bionic-proposed [ppc64el]) for 'qemu-utils'
Suggested packages:
  samba vde2 openbios-ppc openhackware debootstrap
The following packages will be upgraded:
  qemu-block-extra qemu-kvm qemu-system-common qemu-system-ppc qemu-utils
5 upgraded, 0 newly installed, 0 to remove and 18 not upgraded.
Need to get 8476 kB of archives.
After this operation, 0 B of additional disk space will be used.
Get:1 http://ports.ubuntu.com/ubuntu-ports bionic-proposed/main ppc64el qemu-utils ppc64el 1:2.11+dfsg-1ubuntu7.10 [787 kB]
Get:2 http://ports.ubuntu.com/ubuntu-ports bionic-proposed/main ppc64el qemu-system-common ppc64el 1:2.11+dfsg-1ubuntu7.10 [662 kB]
Get:3 http://ports.ubuntu.com/ubuntu-ports bionic-proposed/main ppc64el qemu-block-extra ppc64el 1:2.11+dfsg-1ubuntu7.10 [38.4 kB]
Get:4 http://ports.ubuntu.com/ubuntu-ports bionic-proposed/main ppc64el qemu-kvm ppc64el 1:2.11+dfsg-1ubuntu7.10 [12.9 kB]
Get:5 http://ports.ubuntu.com/ubuntu-ports bionic-proposed/main ppc64el qemu-system-ppc ppc64el 1:2.11+dfsg-1ubuntu7.10 [6976 kB]
Fetched 8476 kB in 4s (2067 kB/s)
(Reading database ... 68341 files and directories currently installed.)
Preparing to unpack .../qemu-utils_1%3a2.11+dfsg-1ubuntu7.10_ppc64el.deb ...
Unpacking qemu-utils (1:2.11+dfsg-1ubuntu7.10) over (1:2.11+dfsg-1ubuntu7.9) ...
Preparing to unpack .../qemu-system-common_1%3a2.11+dfsg-1ubuntu7.10_ppc64el.deb ...
Unpacking qemu-system-common (1:2.11+dfsg-1ubuntu7.10) over (1:2.11+dfsg-1ubuntu7.9) ...
Preparing to unpack .../qemu-block-extra_1%3a2.11+dfsg-1ubuntu7.10_ppc64el.deb ...
Unpacking qemu-block-extra:ppc64el (1:2.11+dfsg-1ubuntu7.10) over (1:2.11+dfsg-1ubuntu7.9) ...
Preparing to unpack .../qemu-kvm_1%3a2.11+dfsg-1ubuntu7.10_ppc64el.deb ...
Unpacking qemu-kvm (1:2.11+dfsg-1ubuntu7.10) over (1:2.11+dfsg-1ubuntu7.9) ...
Preparing to unpack .../qemu-system-ppc_1%3a2.11+dfsg-1ubuntu7.10_ppc64el.deb ...
Unpacking qemu-system-ppc (1:2.11+dfsg-1ubuntu7.10) over (1:2.11+dfsg-1ubuntu7.9) ...
Setting up qemu-block-extra:ppc64el (1:2.11+dfsg-1ubuntu7.10) ...
Setting up qemu-utils (1:2.11+dfsg-1ubuntu7.10) ...
Processing triggers for man-db (2.8.3-2ubuntu0.1) ...
Setting up qemu-system-common (1:2.11+dfsg-1ubuntu7.10) ...
Setting up qemu-system-ppc (1:2.11+dfsg-1ubuntu7.10) ...
Setting up qemu-kvm (1:2.11+dfsg-1ubuntu7.10) ...

Retrying the migration case.
Working fine now, from the log:
$ virsh migrate --live --verbose b-x qemu+ssh://10.245.71.179/system
Migration: [100 %]

Setting verified