arm64: uaccess: Add the uaccess_flushcache.c file

The uaccess_flushcache.c file was inadvertently dropped by the
maintainer in a previous commit. Add it back.

Fixes: 5d7bdeb1 ("arm64: uaccess: Implement *_flushcache variants")
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/lib/uaccess_flushcache.c

+/*
+ * Copyright (C) 2017 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/uaccess.h>
+#include <asm/barrier.h>
+#include <asm/cacheflush.h>
+
+void memcpy_flushcache(void *dst, const void *src, size_t cnt)
+{
+	/*
+	 * We assume this should not be called with @dst pointing to
+	 * non-cacheable memory, such that we don't need an explicit
+	 * barrier to order the cache maintenance against the memcpy.
+	 */
+	memcpy(dst, src, cnt);
+	__clean_dcache_area_pop(dst, cnt);
+}
+EXPORT_SYMBOL_GPL(memcpy_flushcache);
+
+void memcpy_page_flushcache(char *to, struct page *page, size_t offset,
+			    size_t len)
+{
+	memcpy_flushcache(to, page_address(page) + offset, len);
+}
+
+unsigned long __copy_user_flushcache(void *to, const void __user *from,
+				     unsigned long n)
+{
+	unsigned long rc = __arch_copy_from_user(to, from, n);
+
+	/* See above */
+	__clean_dcache_area_pop(to, n - rc);
+	return rc;
+}