DO NOT USE THIS! This is the ancient /dev/cpu/microcode interface
which was used by userspace tools like iucode_tool and microcode.ctl.
It is inadequate because it runs too late to be able to properly
load microcode on a machine and it needs special tools. Instead, you
should've switched to the early loading method with the initrd or
builtin microcode by now: Documentation/x86/microcode.rst