KVM: emulator: emulate XLAT

This is used by SGABIOS, KVM breaks with emulate_invalid_guest_state=1.
It is just a MOV in disguise, with a funny source address.
Reported-by: NJun'ichi Nomura <j-nomura@ce.jp.nec.com>
Cc: stable@vger.kernel.org # 3.9
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NGleb Natapov <gleb@redhat.com>

arch/x86/kvm/emulate.c

@@ -60,6 +60,7 @@
 #define OpGS              25ull  /* GS */
 #define OpMem8            26ull  /* 8-bit zero extended memory operand */
 #define OpImm64           27ull  /* Sign extended 16/32/64-bit immediate */
+#define OpXLat            28ull  /* memory at BX/EBX/RBX + zero-extended AL */
 
 #define OpBits             5  /* Width of operand field */
 #define OpMask             ((1ull << OpBits) - 1)
@@ -99,6 +100,7 @@
 #define SrcImmUByte (OpImmUByte << SrcShift)
 #define SrcImmU     (OpImmU << SrcShift)
 #define SrcSI       (OpSI << SrcShift)
+#define SrcXLat     (OpXLat << SrcShift)
 #define SrcImmFAddr (OpImmFAddr << SrcShift)
 #define SrcMemFAddr (OpMemFAddr << SrcShift)
 #define SrcAcc      (OpAcc << SrcShift)
@@ -3959,7 +3961,8 @@ static const struct opcode opcode_table[256] = {
 	G(Src2One | ByteOp, group2), G(Src2One, group2),
 	G(Src2CL | ByteOp, group2), G(Src2CL, group2),
 	I(DstAcc | SrcImmUByte | No64, em_aam),
-	I(DstAcc | SrcImmUByte | No64, em_aad), N, N,
+	I(DstAcc | SrcImmUByte | No64, em_aad), N,
+	I(DstAcc | SrcXLat | ByteOp, em_mov),
 	/* 0xD8 - 0xDF */
 	N, E(0, &escape_d9), N, E(0, &escape_db), N, E(0, &escape_dd), N, N,
 	/* 0xE0 - 0xE7 */
@@ -4221,6 +4224,16 @@ static int decode_operand(struct x86_emulate_ctxt *ctxt, struct operand *op,
 		op->val = 0;
 		op->count = 1;
 		break;
+	case OpXLat:
+		op->type = OP_MEM;
+		op->bytes = (ctxt->d & ByteOp) ? 1 : ctxt->op_bytes;
+		op->addr.mem.ea =
+			register_address(ctxt,
+				reg_read(ctxt, VCPU_REGS_RBX) +
+				(reg_read(ctxt, VCPU_REGS_RAX) & 0xff));
+		op->addr.mem.seg = seg_override(ctxt);
+		op->val = 0;
+		break;
 	case OpImmFAddr:
 		op->type = OP_IMM;
 		op->addr.mem.ea = ctxt->_eip;