KVM: x86 emulator: introduce Op3264 for mov cr and mov dr instructions

The operands for these instructions are 32 bits or 64 bits, depending on
long mode, and ignoring REX prefixes, or the operand size prefix.
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/emulate.c

@@ -83,6 +83,7 @@
 #define Group       (1<<14)     /* Bits 3:5 of modrm byte extend opcode */
 #define GroupDual   (1<<15)     /* Alternate decoding of mod == 3 */
 /* Misc flags */
+#define Op3264      (1<<24) /* Operand is 64b in long mode, 32b otherwise */
 #define Undefined   (1<<25) /* No Such Instruction */
 #define Lock        (1<<26) /* lock prefix is allowed for the instruction */
 #define Priv        (1<<27) /* instruction generates #GP if current CPL != 0 */
@@ -2406,6 +2407,13 @@ x86_decode_insn(struct x86_emulate_ctxt *ctxt)
 	if (mode == X86EMUL_MODE_PROT64 && (c->d & Stack))
 		c->op_bytes = 8;
 
+	if (c->d & Op3264) {
+		if (mode == X86EMUL_MODE_PROT64)
+			c->op_bytes = 8;
+		else
+			c->op_bytes = 4;
+	}
+
 	/* ModRM and SIB bytes. */
 	if (c->d & ModRM) {
 		rc = decode_modrm(ctxt, ops);