[PATCH 11/13] mm: extend prefault helpers to fault in more than PAGE_SIZE

Daniel Vetter
2011-11-06T19:13:58Z

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

I've checked the callsites and they all already clamp size when
calling fault_in_pages_* to the same as for the subsequent
__copy_to|from_user and hence don't rely on the implicit clamping
to PAGE_SIZE.

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

Cc: linux-mm@kvack.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
include/linux/pagemap.h | 28 ++++++++++++++++++----------
1 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index cfaaa69..689527d 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -408,6 +408,7 @@ extern void add_page_wait_queue(struct page *page, wait_queue_t *waiter);
static inline int fault_in_pages_writeable(char __user *uaddr, int size)
{
int ret;
+ char __user *end = uaddr + size - 1;

if (unlikely(size == 0))
return 0;
@@ -416,17 +417,20 @@ static inline int fault_in_pages_writeable(char __user *uaddr, int size)
* Writing zeroes into userspace here is OK, because we know that if
* the zero gets there, we'll be overwriting it.
*/
- ret = __put_user(0, uaddr);
+ while (uaddr <= end) {
+ ret = __put_user(0, uaddr);
+ if (ret != 0)
+ return ret;
+ uaddr += PAGE_SIZE;
+ }
if (ret == 0) {
- char __user *end = uaddr + size - 1;
-
/*
* If the page was already mapped, this will get a cache miss
* for sure, so try to avoid doing it.
*/
- if (((unsigned long)uaddr & PAGE_MASK) !=
+ if (((unsigned long)uaddr & PAGE_MASK) ==
((unsigned long)end & PAGE_MASK))
- ret = __put_user(0, end);
+ ret = __put_user(0, end);
}
return ret;
}
@@ -435,17 +439,21 @@ static inline int fault_in_pages_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;

- ret = __get_user(c, uaddr);
+ while (uaddr <= end) {
+ ret = __get_user(c, uaddr);
+ if (ret != 0)
+ return ret;
+ uaddr += PAGE_SIZE;
+ }
if (ret == 0) {
- const char __user *end = uaddr + size - 1;
-
- if (((unsigned long)uaddr & PAGE_MASK) !=
+ if (((unsigned long)uaddr & PAGE_MASK) ==
((unsigned long)end & PAGE_MASK)) {
- ret = __get_user(c, end);
+ ret = __get_user(c, end);
(void)c;
}
}
--
1.7.6.4

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