AMD has at long last coughed up the stuff to the linux-firmware people
https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/...
The fam15h microcode update adds IBPB
* Indirect Branch Prediction Barrier (IBPB) * PRED_CMD MSR is available: YES * CPU indicates IBPB capability: YES (IBPB_SUPPORT feature bit)
The question is what about the other stuff? IBRS, STIBP? This is confusing due to zero documentation on these updates from amd...Why don't they have those in this update? Would it be possible to easily add the support flags without microcode for those who use libreboot?
Would it still be a good idea to add the lfence msr as rmarek mentioned?
As this is all above my pay-grade I would very much appreciate one of the experts to chime in.