The reg-reg forms should cause #UD; they come into existence only with APX, where MOVBE also extends BSWAP (for the latter not being "eligible" to a REX2 prefix).
Signed-off-by: Jan Beulich <[email protected]> --- a/xen/arch/x86/x86_emulate/x86_emulate.c +++ b/xen/arch/x86/x86_emulate/x86_emulate.c @@ -6824,6 +6824,7 @@ x86_emulate( case X86EMUL_OPC(0x0f38, 0xf0): /* movbe m,r */ case X86EMUL_OPC(0x0f38, 0xf1): /* movbe r,m */ + generate_exception_if(ea.type != OP_MEM, X86_EXC_UD); vcpu_must_have(movbe); switch ( op_bytes ) {
