It's worth noting that KVM doesn't allow remapping the APIC base address at all: https://github.com/torvalds/linux/blob/49d7c6559bf2ab4f1d56b...
(If KVM allowed moving the APIC, then you could use this to escalate privileges from guest kernel mode to /guest/ SMM, and KVM is adding guest SMM soon, but that's a much less interesting attack IMO.)