arm64: User access library functions

This patch add support for various user access functions. These
functions use the standard LDR/STR instructions and not the LDRT/STRT
variants in order to allow kernel addresses (after set_fs(KERNEL_DS)).

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Olof Johansson <olof@lixom.net>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>

arch/arm64/lib/copy_from_user.S

@@ -0,0 +1,66 @@
+/*
+ * Copyright (C) 2012 ARM Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/linkage.h>
+#include <asm/assembler.h>
+
+/*
+ * Copy from user space to a kernel buffer (alignment handled by the hardware)
+ *
+ * Parameters:
+ *	x0 - to
+ *	x1 - from
+ *	x2 - n
+ * Returns:
+ *	x0 - bytes not copied
+ */
+ENTRY(__copy_from_user)
+	add	x4, x1, x2			// upper user buffer boundary
+	subs	x2, x2, #8
+	b.mi	2f
+1:
+USER(9f, ldr	x3, [x1], #8	)
+	subs	x2, x2, #8
+	str	x3, [x0], #8
+	b.pl	1b
+2:	adds	x2, x2, #4
+	b.mi	3f
+USER(9f, ldr	w3, [x1], #4	)
+	sub	x2, x2, #4
+	str	w3, [x0], #4
+3:	adds	x2, x2, #2
+	b.mi	4f
+USER(9f, ldrh	w3, [x1], #2	)
+	sub	x2, x2, #2
+	strh	w3, [x0], #2
+4:	adds	x2, x2, #1
+	b.mi	5f
+USER(9f, ldrb	w3, [x1]	)
+	strb	w3, [x0]
+5:	mov	x0, #0
+	ret
+ENDPROC(__copy_from_user)
+
+	.section .fixup,"ax"
+	.align	2
+9:	sub	x2, x4, x1
+	mov	x3, x2
+10:	strb	wzr, [x0], #1			// zero remaining buffer space
+	subs	x3, x3, #1
+	b.ne	10b
+	mov	x0, x2				// bytes not copied
+	ret
+	.previous