MIPS: Check TLB before handle_ri_rdhwr() for Loongson-3

Loongson-3's micro TLB (ITLB) is not strictly a subset of JTLB. That
means: when a JTLB entry is replaced by hardware, there may be an old
valid entry exists in ITLB. So, a TLB miss exception may occur while
handle_ri_rdhwr() is running because it try to access EPC's content.
However, handle_ri_rdhwr() doesn't clear EXL, which makes a TLB Refill
exception be treated as a TLB Invalid exception and tlbp may fail. In
this case, if FTLB (which is usually set-associative instead of set-
associative) is enabled, a tlbp failure will cause an invalid tlbwi,
which will hang the whole system.

This patch rename handle_ri_rdhwr_vivt to handle_ri_rdhwr_tlbp and use
it for Loongson-3. It try to solve the same problem described as below,
but more straightforwards.

https://patchwork.linux-mips.org/patch/12591/

I think Loongson-2 has the same problem, but it has no FTLB, so we just
keep it as is.

Signed-off-by: Huacai Chen <chenhc@lemote.com>
Cc: Rui Wang <wangr@lemote.com>
Cc: John Crispin <john@phrozen.org>
Cc: Steven J . Hill <Steven.Hill@caviumnetworks.com>
Cc: Fuxin Zhang <zhangfx@lemote.com>
Cc: Zhangjin Wu <wuzhangjin@gmail.com>
Cc: Huacai Chen <chenhc@lemote.com>
Cc: linux-mips@linux-mips.org
Cc: stable@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/15753/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/genex.S

@@ -519,7 +519,7 @@ NESTED(nmi_handler, PT_SIZE, sp)
 	BUILD_HANDLER reserved reserved sti verbose	/* others */
 
 	.align	5
-	LEAF(handle_ri_rdhwr_vivt)
+	LEAF(handle_ri_rdhwr_tlbp)
 	.set	push
 	.set	noat
 	.set	noreorder
@@ -538,7 +538,7 @@ NESTED(nmi_handler, PT_SIZE, sp)
 	.set	pop
 	bltz	k1, handle_ri	/* slow path */
 	/* fall thru */
-	END(handle_ri_rdhwr_vivt)
+	END(handle_ri_rdhwr_tlbp)
 
 	LEAF(handle_ri_rdhwr)
 	.set	push

arch/mips/kernel/traps.c

@@ -83,7 +83,7 @@ extern asmlinkage void handle_dbe(void);
 extern asmlinkage void handle_sys(void);
 extern asmlinkage void handle_bp(void);
 extern asmlinkage void handle_ri(void);
-extern asmlinkage void handle_ri_rdhwr_vivt(void);
+extern asmlinkage void handle_ri_rdhwr_tlbp(void);
 extern asmlinkage void handle_ri_rdhwr(void);
 extern asmlinkage void handle_cpu(void);
 extern asmlinkage void handle_ov(void);
@@ -2408,9 +2408,18 @@ void __init trap_init(void)
 
 	set_except_vector(EXCCODE_SYS, handle_sys);
 	set_except_vector(EXCCODE_BP, handle_bp);
-	set_except_vector(EXCCODE_RI, rdhwr_noopt ? handle_ri :
-			  (cpu_has_vtag_icache ?
-			   handle_ri_rdhwr_vivt : handle_ri_rdhwr));
+
+	if (rdhwr_noopt)
+		set_except_vector(EXCCODE_RI, handle_ri);
+	else {
+		if (cpu_has_vtag_icache)
+			set_except_vector(EXCCODE_RI, handle_ri_rdhwr_tlbp);
+		else if (current_cpu_type() == CPU_LOONGSON3)
+			set_except_vector(EXCCODE_RI, handle_ri_rdhwr_tlbp);
+		else
+			set_except_vector(EXCCODE_RI, handle_ri_rdhwr);
+	}
+
 	set_except_vector(EXCCODE_CPU, handle_cpu);
 	set_except_vector(EXCCODE_OV, handle_ov);
 	set_except_vector(EXCCODE_TR, handle_tr);