Comment 3 for bug 1874647

The case with the module parameter in SEV needs a fix similar to
  https://libvirt.org/git/?p=libvirt.git;a=commit;h=b183a75319b90d0af5512be513743e1eab950612
as it can be re-loaded at any time.

Essentially the checks in virQEMUCapsLoadCache check qemu/kernel version and many other things.
They also check microcode version ...

I think the decision there can be two ways, either "on any reboot we need to refresh caps" which makes the code small but probably also wastes quite some refreshes that were not needed.
Or it could along all the versions that it checks also keep a full string of /proc/cmdline and compare it. If changed it needs to be refreshed.

I agree to Frank that this should be reported upstream.
No matter if you or I write a fix, it needs to go upstream then - so a bug tracker there can't hurt.
OTOH you can as well start right away with a RFC patch there if you have something prepared already - there is no "strict need" for an upstream bug, only if you hope someone there will fix it for you.

Since workarounds are available the prio is medium IMHO, eager to see what upstream thinks.

P.S. Even if you have no patch, it would be great if you (as the affected) would kick off the discussion upstream. Please provide a link here to the mailing list entry.