mm/gup: Provide callback to check if __GUP_fast() is allowed for the range

This is a preparation patch for the transition of x86 to the generic GUP_fast()
implementation.

On x86, get_user_pages_fast() does a couple of sanity checks to see if we can
call __get_user_pages_fast() for the range.

This kind of wrapping protection should be useful for the generic code too.

Signed-off-by: Kirill A. Shutemov <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Aneesh Kumar K . V <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Dann Frazier <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Steve Capper <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
[ Small readability edits. ]
Signed-off-by: Ingo Molnar <[email protected]>

diff --git a/mm/gup.c b/mm/gup.c
index e3d1e80424f495a944132aaf635e412b5a35db10..527ec2c6cca3b758eeb9a5e353b4075146fe8634 100644 (file)
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1614,6 +1614,21 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
        return nr;
 }
 
+#ifndef gup_fast_permitted
+/*
+ * Check if it's allowed to use __get_user_pages_fast() for the range, or
+ * we need to fall back to the slow version:
+ */
+bool gup_fast_permitted(unsigned long start, int nr_pages, int write)
+{
+       unsigned long len, end;
+
+       len = (unsigned long) nr_pages << PAGE_SHIFT;
+       end = start + len;
+       return end >= start;
+}
+#endif
+
 /**
  * get_user_pages_fast() - pin user pages in memory
  * @start:     starting user address
@@ -1633,11 +1648,14 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
                        struct page **pages)
 {
-       int nr, ret;
+       int nr = 0, ret = 0;
 
        start &= PAGE_MASK;
-       nr = __get_user_pages_fast(start, nr_pages, write, pages);
-       ret = nr;
+
+       if (gup_fast_permitted(start, nr_pages, write)) {
+               nr = __get_user_pages_fast(start, nr_pages, write, pages);
+               ret = nr;
+       }
 
        if (nr < nr_pages) {
                /* Try to get the remaining pages with get_user_pages */