>>chei0a+(OP)
"System management mode" is a tremendous wart and should be removed wholesale, with Intel adopting a more ARM-style trusted boot chain with explicit cooperation from the OS or hypervisor. And while you're at it, kill UEFI and install a pony for me.
(Seriously, SMM serves either bizarre ILO features that high-end vendors like but are rarely used, or security agencies looking for a layer to hide in.)