1 files changed, 62 insertions, 2 deletions

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index cfaaa6949b8..efa26b4da8d 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -426,7 +426,7 @@ static inline int fault_in_pages_writeable(char __user *uaddr, int size)
 		 */
 		if (((unsigned long)uaddr & PAGE_MASK) !=
 				((unsigned long)end & PAGE_MASK))
-		 	ret = __put_user(0, end);
+			ret = __put_user(0, end);
 	}
 	return ret;
 }
@@ -445,13 +445,73 @@ static inline int fault_in_pages_readable(const char __user *uaddr, int size)
 
 		if (((unsigned long)uaddr & PAGE_MASK) !=
 				((unsigned long)end & PAGE_MASK)) {
-		 	ret = __get_user(c, end);
+			ret = __get_user(c, end);
 			(void)c;
 		}
 	}
 	return ret;
 }
 
+/*
+ * Multipage variants of the above prefault helpers, useful if more than
+ * PAGE_SIZE of data needs to be prefaulted. These are separate from the above
+ * functions (which only handle up to PAGE_SIZE) to avoid clobbering the
+ * filemap.c hotpaths.
+ */
+static inline int fault_in_multipages_writeable(char __user *uaddr, int size)
+{
+	int ret;
+	char __user *end = uaddr + size - 1;
+
+	if (unlikely(size == 0))
+		return 0;
+
+	/*
+	 * Writing zeroes into userspace here is OK, because we know that if
+	 * the zero gets there, we'll be overwriting it.
+	 */
+	while (uaddr <= end) {
+		ret = __put_user(0, uaddr);
+		if (ret != 0)
+			return ret;
+		uaddr += PAGE_SIZE;
+	}
+
+	/* Check whether the range spilled into the next page. */
+	if (((unsigned long)uaddr & PAGE_MASK) ==
+			((unsigned long)end & PAGE_MASK))
+		ret = __put_user(0, end);
+
+	return ret;
+}
+
+static inline int fault_in_multipages_readable(const char __user *uaddr,
+					       int size)
+{
+	volatile char c;
+	int ret;
+	const char __user *end = uaddr + size - 1;
+
+	if (unlikely(size == 0))
+		return 0;
+
+	while (uaddr <= end) {
+		ret = __get_user(c, uaddr);
+		if (ret != 0)
+			return ret;
+		uaddr += PAGE_SIZE;
+	}
+
+	/* Check whether the range spilled into the next page. */
+	if (((unsigned long)uaddr & PAGE_MASK) ==
+			((unsigned long)end & PAGE_MASK)) {
+		ret = __get_user(c, end);
+		(void)c;
+	}
+
+	return ret;
+}
+
 int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
 				pgoff_t index, gfp_t gfp_mask);
 int add_to_page_cache_lru(struct page *page, struct address_space *mapping,