KVM: x86 emulator: fix access registers for instructions with ModR/M byte and Mod = 3

The patch belows changes the access type to register from memory for
instructions that are declared as SrcMem or DstMem, but have a
ModR/M byte with Mod = 3.

It fixes (at least) the lmsw and smsw instructions on an AMD64 CPU,
which are needed for FreeBSD.
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>
Signed-off-by: NAvi Kivity <avi@qumranet.com>

drivers/kvm/x86_emulate.c

@@ -825,6 +825,14 @@ x86_emulate_memop(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
 		if (twobyte && b == 0x01 && modrm_reg == 7)
 			break;
 	      srcmem_common:
+		/*
+		 * For instructions with a ModR/M byte, switch to register
+		 * access if Mod = 3.
+		 */
+		if ((d & ModRM) && modrm_mod == 3) {
+			src.type = OP_REG;
+			break;
+		}
 		src.type = OP_MEM;
 		src.ptr = (unsigned long *)cr2;
 		src.val = 0;
@@ -893,6 +901,14 @@ x86_emulate_memop(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
 		dst.ptr = (unsigned long *)cr2;
 		dst.bytes = (d & ByteOp) ? 1 : op_bytes;
 		dst.val = 0;
+		/*
+		 * For instructions with a ModR/M byte, switch to register
+		 * access if Mod = 3.
+		 */
+		if ((d & ModRM) && modrm_mod == 3) {
+			dst.type = OP_REG;
+			break;
+		}
 		if (d & BitOp) {
 			unsigned long mask = ~(dst.bytes * 8 - 1);