This related RHEL article contains some information about the various mitigations they use (PTI, IBRS, IBPB, i.e. Page Table Isolation, Indirect Branch Restrict

This related RHEL article contains some information about the various mitigations they use (PTI, IBRS, IBPB, i.e. Page Table Isolation, Indirect Branch Restricted Speculation, and Indirect Branch Prediction Barriers) and their relation to the Intel and AMD microcode updates: https://access.redhat.com/articles/3311301 https://access.redhat.com/articles/3311301 It does not really answer all my questions about the microcode updates, but I have not seen any more comprehensive writeups yet.