KVM: X86: Allow userspace to define the microcode version

KVM: X86: Allow userspace to define the microcode version

Linux (among the others) has checks to make sure that certain features
aren't enabled on a certain family/model/stepping if the microcode version
isn't greater than or equal to a known good version.

By exposing the real microcode version, we're preventing buggy guests that
don't check that they are running virtualized (i.e., they should trust the
hypervisor) from disabling features that are effectively not buggy.

Suggested-by: Filippo Sironi <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Radim Krčmář <[email protected]>
Cc: Liran Alon <[email protected]>
Cc: Nadav Amit <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Tom Lendacky <[email protected]>
Signed-off-by: Wanpeng Li <[email protected]>
Reviewed-by: Paolo Bonzini <[email protected]>
Signed-off-by: Radim Krčmář <[email protected]>