mm: extend prefault helpers to fault in more than PAGE_SIZE
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.
v2: As suggested by Andrew Morton, add a multipage parameter to both
functions to avoid the additional branch for the pagemap.c hotpath.
My gcc 4.6 here seems to dtrt and indeed reap these branches where not
needed.
v3: Becaus I couldn't find a way around adding a uaddr += PAGE_SIZE to
the filemap.c hotpaths (that the compiler couldn't remove again),
let's go with separate new functions for the multipage use-case.
v4: Adjust comment to CodingStlye and fix spelling.
Acked-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index cfaaa69..c93a9a9 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -426,7 +426,7 @@
*/
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 @@
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;
+ 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.
+ */
+ 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,