mm/gup: introduce pin_user_pages_fast_only()

This is the FOLL_PIN equivalent of __get_user_pages_fast(), except with a
more descriptive name, and gup_flags instead of a boolean "write" in the
argument list.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@linux.ie>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: "Joonas Lahtinen" <joonas.lahtinen@linux.intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Souptick Joarder <jrdr.linux@gmail.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://lkml.kernel.org/r/20200519002124.2025955-4-jhubbard@nvidia.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/mm.h b/include/linux/mm.h
index e6b8847..6c236c5 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1827,6 +1827,8 @@ extern int mprotect_fixup(struct vm_area_struct *vma,
  */
 int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
                          struct page **pages);
+int pin_user_pages_fast_only(unsigned long start, int nr_pages,
+                            unsigned int gup_flags, struct page **pages);
 /*
  * per-process(per-mm_struct) statistics.
  */

diff --git a/mm/gup.c b/mm/gup.c
index 67b5e96..0702c1a 100644 (file)
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2917,6 +2917,42 @@ int pin_user_pages_fast(unsigned long start, int nr_pages,
 }
 EXPORT_SYMBOL_GPL(pin_user_pages_fast);
 
+/*
+ * This is the FOLL_PIN equivalent of __get_user_pages_fast(). Behavior is the
+ * same, except that this one sets FOLL_PIN instead of FOLL_GET.
+ *
+ * The API rules are the same, too: no negative values may be returned.
+ */
+int pin_user_pages_fast_only(unsigned long start, int nr_pages,
+                            unsigned int gup_flags, struct page **pages)
+{
+       int nr_pinned;
+
+       /*
+        * FOLL_GET and FOLL_PIN are mutually exclusive. Note that the API
+        * rules require returning 0, rather than -errno:
+        */
+       if (WARN_ON_ONCE(gup_flags & FOLL_GET))
+               return 0;
+       /*
+        * FOLL_FAST_ONLY is required in order to match the API description of
+        * this routine: no fall back to regular ("slow") GUP.
+        */
+       gup_flags |= (FOLL_PIN | FOLL_FAST_ONLY);
+       nr_pinned = internal_get_user_pages_fast(start, nr_pages, gup_flags,
+                                                pages);
+       /*
+        * This routine is not allowed to return negative values. However,
+        * internal_get_user_pages_fast() *can* return -errno. Therefore,
+        * correct for that here:
+        */
+       if (nr_pinned < 0)
+               nr_pinned = 0;
+
+       return nr_pinned;
+}
+EXPORT_SYMBOL_GPL(pin_user_pages_fast_only);
+
 /**
  * pin_user_pages_remote() - pin pages of a remote process (task != current)
  *