Comment 39 for bug 1853200

A while back Marc checked the case and realize that backporting the qemu changes without anything in libvirt would make no sense - comment #21.
Now the things in libvirt exist, which is a step forward.

This still will be no transparent solution, people will have to switch types if they can't run the old types. And it appears that if one is willing to change the cpu-model, he could also add feature-disable hle/rtm with the same effort.

The special case is for situations in which people can select cpu-models but not define custom features - for those backporting these would help to mitigate the impact of the CVE related TSX/TAA kernel changes that started all of this.

I'd suggest to let this mature in focal for a few days, see if people or tests run into issues. And then ask Marc to re-evaluate again.
I'll add qemu/libvirt backport tasks and assign them to Ubuntu security - so that they can comment on what the think (now with the libvirt changes existing).