nds32: MMU fault handling and page table management

This patch includes page fault handler, mmap and fixup implementations.

Signed-off-by: Vincent Chen <vincentc@andestech.com>
Signed-off-by: Greentime Hu <greentime@andestech.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>

arch/nds32/lib/copy_page.S

@@ -0,0 +1,37 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2005-2017 Andes Technology Corporation
+
+#include <linux/linkage.h>
+#include <asm/page.h>
+
+	.text
+ENTRY(copy_page)
+	pushm	$r2, $r10
+	movi	$r2, PAGE_SIZE >> 5
+.Lcopy_loop:
+	lmw.bim	$r3, [$r1], $r10
+	smw.bim	$r3, [$r0], $r10
+	subi45	$r2, #1
+	bnez38	$r2, .Lcopy_loop
+	popm	$r2, $r10
+	ret
+ENDPROC(copy_page)
+
+ENTRY(clear_page)
+	pushm	$r1, $r9
+	movi	$r1, PAGE_SIZE >> 5
+	movi55	$r2, #0
+	movi55	$r3, #0
+	movi55	$r4, #0
+	movi55	$r5, #0
+	movi55	$r6, #0
+	movi55	$r7, #0
+	movi55	$r8, #0
+	movi55	$r9, #0
+.Lclear_loop:
+	smw.bim	$r2, [$r0], $r9
+	subi45	$r1, #1
+	bnez38	$r1, .Lclear_loop
+	popm	$r1, $r9
+        ret
+ENDPROC(clear_page)

arch/nds32/mm/extable.c

@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2005-2017 Andes Technology Corporation
+
+#include <linux/extable.h>
+#include <linux/uaccess.h>
+
+int fixup_exception(struct pt_regs *regs)
+{
+	const struct exception_table_entry *fixup;
+
+	fixup = search_exception_tables(instruction_pointer(regs));
+	if (fixup)
+		regs->ipc = fixup->fixup;
+
+	return fixup != NULL;
+}