commit 9e8919ae upstream.

Return unhandlable error on inter-privilege level ret instruction.  This is
since the current emulation does not check the privilege level correctly when
loading the CS, and does not pop RSP/SS as needed.
Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>