On Thu,  1 Mar 2012 20:22:59 +0100
Daniel Vetter [off-list ref] wrote:

drm/i915 wants to read/write more than one page in its fastpath
and hence needs to prefault more than PAGE_SIZE bytes.

Add new functions in filemap.h to make that possible.

Also kill a copy&pasted spurious space in both functions while at it.


...

+/* Multipage variants of the above prefault helpers, useful if more than
+ * PAGE_SIZE of date 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. */

Like this please:

/*
 * Multipage variants of the above prefault helpers, useful if more than
 * PAGE_SIZE of date 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.
 */

and s/date/data/

+static inline int fault_in_multipages_writeable(char __user *uaddr, int size)
+{
+	int ret;
+	const 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.
+	 */

Yeah, like that.

+	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;
+}

Please merge it via the DRI tree.

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