Comment 4 for bug 1840745

Bionic as-is:
qemu-system-x86_64 -cpu ? | grep ssb
  avx512-4vnniw avx512-4fmaps md-clear spec-ctrl arch-capabilities ssbd
  wbnoinvd ibpb virt-ssbd
  rdctl-no ibrs-all rsba skip-l1dfl-vmentry ssb-no mds-no

Upgrade to proposed:
root@b-testkvm:~# apt install qemu-utils qemu-system-x86 qemu-system-common qemu-block-extra
Reading package lists... Done
Building dependency tree
Reading state information... Done
Suggested packages:
  samba vde2 sgabios ovmf debootstrap
The following packages will be upgraded:
  qemu-block-extra qemu-system-common qemu-system-x86 qemu-utils
4 upgraded, 0 newly installed, 0 to remove and 40 not upgraded.
Need to get 6782 kB of archives.
After this operation, 4096 B of additional disk space will be used.
Get:1 http://archive.ubuntu.com/ubuntu bionic-proposed/main amd64 qemu-utils amd64 1:2.11+dfsg-1ubuntu7.18 [866 kB]
Get:2 http://archive.ubuntu.com/ubuntu bionic-proposed/main amd64 qemu-system-common amd64 1:2.11+dfsg-1ubuntu7.18 [672 kB]
Get:3 http://archive.ubuntu.com/ubuntu bionic-proposed/main amd64 qemu-block-extra amd64 1:2.11+dfsg-1ubuntu7.18 [40.1 kB]
Get:4 http://archive.ubuntu.com/ubuntu bionic-proposed/main amd64 qemu-system-x86 amd64 1:2.11+dfsg-1ubuntu7.18 [5203 kB]
Fetched 6782 kB in 1s (8675 kB/s)
(Reading database ... 30081 files and directories currently installed.)
Preparing to unpack .../qemu-utils_1%3a2.11+dfsg-1ubuntu7.18_amd64.deb ...
Unpacking qemu-utils (1:2.11+dfsg-1ubuntu7.18) over (1:2.11+dfsg-1ubuntu7.17) ...
Preparing to unpack .../qemu-system-common_1%3a2.11+dfsg-1ubuntu7.18_amd64.deb ...
Unpacking qemu-system-common (1:2.11+dfsg-1ubuntu7.18) over (1:2.11+dfsg-1ubuntu7.17) ...
Preparing to unpack .../qemu-block-extra_1%3a2.11+dfsg-1ubuntu7.18_amd64.deb ...
Unpacking qemu-block-extra:amd64 (1:2.11+dfsg-1ubuntu7.18) over (1:2.11+dfsg-1ubuntu7.17) ...
Preparing to unpack .../qemu-system-x86_1%3a2.11+dfsg-1ubuntu7.18_amd64.deb ...
Unpacking qemu-system-x86 (1:2.11+dfsg-1ubuntu7.18) over (1:2.11+dfsg-1ubuntu7.17) ...
Setting up qemu-block-extra:amd64 (1:2.11+dfsg-1ubuntu7.18) ...
Setting up qemu-utils (1:2.11+dfsg-1ubuntu7.18) ...
Setting up qemu-system-common (1:2.11+dfsg-1ubuntu7.18) ...
Setting up qemu-system-x86 (1:2.11+dfsg-1ubuntu7.18) ...
Processing triggers for man-db (2.8.3-2ubuntu0.1) ...

With the new code:
root@b-testkvm:~# qemu-system-x86_64 -cpu ? | grep ssb
  avx512-4vnniw avx512-4fmaps md-clear spec-ctrl arch-capabilities ssbd
  wbnoinvd ibpb amd-ssbd virt-ssbd amd-no-ssb
  rdctl-no ibrs-all rsba skip-l1dfl-vmentry ssb-no mds-no

We see the new features amd-ssbd and amd-no-ssb
verified for qemu - libvirt isn't accepted in proposed yet.