So, in any case we may not be able to disable machine-check
exceptions
(MCEs) only within the context of kexec'ed kernel. Let me know if I've
missed something here.
You can disable signalling in the main machine check register,
then you won't get any machine check interrupts. No need to mess
with any CPU specific banks.
See the old mce tree that
kernel.org ate for a patch that just did that
during the kcore copy.
-Andi