Wrote my son who works at AMD but in the Radeon division, but not the cpu side.
I asked, 'Are the fixes that Microsoft and Linux distros are sending out to fix the problems in the cpu's, just software fixes for the OS kernel and software interacting with the cpu, or will there be some 'firmware' fixes for the cpu itself that will be flashed somehow that will alter the function of the cpu ? If the chip gets changed, the recovery with a non-bootable computer seems pretty awkward. And scary.'
He answered, (and this isn't really much help to us), "I don't really know the answer, sorry. I suspect that Microsoft is just altering Windows code, and not CPU microcode, but who knows."
I assume that assumption is right, but my goodness, imagine if they 'fix' the chip and it goes wrong. Surely they wouldn't try to do that.