On 22/05/2018 07:03, Taiidan@gmx.com wrote:
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?
What you mean with "add the support flags without microcode"?
A CPU either supports some instructions (like IBPB) because it actually does (i.e. the microcode tells it how to do that), or it does not.
I don't know if you can fake enable these support flags, but I don't think it is a good idea at all, at best it would just be a lie, at worst it could cause issues (crashing?) if the kernel calls an instruction that isn't available (I don't know how that is handled).
-Alberto