MIPS: R5900: Verify that the TLB refill handler does not overflow

The R5900 TLB refill handler is limited to 32 instructions (0x80 bytes,
which is 0x80000080 - 0x80000000) according to the TX79 manual[1]:

        Table 5-2. Exception Vectors for Level 1 exceptions

             Exceptions      |      Vector Address
                             |   BEV = 0  |   BEV = 1
        ---------------------+------------+-----------
        TLB Refill (EXL = 0) | 0x80000000 | 0xBFC00200
        TLB Refill (EXL = 1) | 0x80000180 | 0xBFC00380
        Interrupt            | 0x80000200 | 0xBFC00400
        Others               | 0x80000180 | 0xBFC00380
        ---------------------+------------+-----------

        Table 5-3. Exception Vectors for Level 2 exceptions

             Exceptions      |      Vector Address
                             |   DEV = 0  |   DEV = 1
        ---------------------+------------+-----------
        Reset, NMI           | 0xBFC00000 | 0xBFC00000
        Performance Counter  | 0x80000080 | 0xBFC00280
        Debug, SIO           | 0x80000100 | 0xBFC00300
        ---------------------+------------+-----------

Reference:

[1] "TX System RISC TX79 Core Architecture" manual, revision 2.0,
    Toshiba Corporation, p. 5-7, https://wiki.qemu.org/File:C790.pdf

Signed-off-by: Fredrik Noring <[email protected]>

arch/mips/mm/tlbex.c

@@ -1399,6 +1399,10 @@ static void build_r4000_tlb_refill_handler(void)
 	 * unused.
 	 */
 	switch (boot_cpu_type()) {
+	case CPU_R5900:
+		if ((p - tlb_handler) > 32)
+			panic("TLB refill handler space exceeded");
+		/* Fallthrough */
 	default:
 		if (sizeof(long) == 4) {
 	case CPU_LOONGSON2: