commit dd598091 upstream.

The KVM emulator code assumes that the guest virtual address space (in 64-bit)
is 48-bits wide.  Since we are about to add more code that makes the same
assumption, this patch adds an assertion to make sure guest virtual address
space is indeed 48-bits wide.
Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Bruce Rogers <brogers@suse.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>