This updated microcode supersedes microcode provided by Red Hat with
the CVE-2017-5715 (“Spectre”) CPU branch injection vulnerability
mitigation.
Historically, Red Hat has provided updated microcode, developed by our
microprocessor partners, as a customer convenience. Red Hat had
temporarily suspended this practice while microcode stabilized. Red
Hat is once again providing an updated Intel microcode package
(microcode_ctl) and AMD microcode package (linux-firmware) to customers
in order to simplify deployment processes and minimize downtime.  We’ll
continue to update these microcode packages as necessary. Please
contact your hardware vendor to determine whether more recent
BIOS/firmware updates are recommended because additional improvements
may be available.
This kbase https://access.redhat.com/articles/3436091 includes a table
that maps Intel and AMD CPU processor code family names to updated
Intel and AMD microcode package versions.