KVM: x86 emulator: Add std and cld instructions (opcodes 0xfc-0xfd)

This adds the std and cld instructions to the emulator.

Encountered while running the BIOS with invalid guest
state emulation enabled.
Signed-off-by: Mohammed Gamal <m.gamal005@gmail.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

arch/x86/kvm/x86_emulate.c

@@ -187,7 +187,7 @@ static u16 opcode_table[256] = {
 	ImplicitOps, ImplicitOps, Group | Group3_Byte, Group | Group3,
 	/* 0xF8 - 0xFF */
 	ImplicitOps, 0, ImplicitOps, ImplicitOps,
-	0, 0, Group | Group4, Group | Group5,
+	ImplicitOps, ImplicitOps, Group | Group4, Group | Group5,
 };
 
 static u16 twobyte_table[256] = {
@@ -1762,6 +1762,14 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
 		ctxt->eflags |= X86_EFLAGS_IF;
 		c->dst.type = OP_NONE;	/* Disable writeback. */
 		break;
+	case 0xfc: /* cld */
+		ctxt->eflags &= ~EFLG_DF;
+		c->dst.type = OP_NONE;	/* Disable writeback. */
+		break;
+	case 0xfd: /* std */
+		ctxt->eflags |= EFLG_DF;
+		c->dst.type = OP_NONE;	/* Disable writeback. */
+		break;
 	case 0xfe ... 0xff:	/* Grp4/Grp5 */
 		rc = emulate_grp45(ctxt, ops);
 		if (rc != 0)