[PATCH v2 1/2] mm/gup: introduce pin_user_pages_unlocked

[John Hubbard]

Introduce pin_user_pages_unlocked(), which is nearly identical to the
get_user_pages_unlocked() that it wraps, except that it sets FOLL_PIN
and rejects FOLL_GET.

As with other pairs of get_user_pages*() and pin_user_pages() API calls,
it's prudent to assert that FOLL_PIN is *not* set in the
get_user_pages*() call, so add that as part of this.

Cc: Souptick Joarder <jrdr.li...@gmail.com>
Signed-off-by: John Hubbard <jhubb...@nvidia.com>
---
 include/linux/mm.h |  2 ++
 mm/gup.c           | 23 +++++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index f3fe7371855c..a84befdb54b2 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1713,6 +1713,8 @@ long get_user_pages_locked(unsigned long start, unsigned 
long nr_pages,
                    unsigned int gup_flags, struct page **pages, int *locked);
 long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
                    struct page **pages, unsigned int gup_flags);
+long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
+                   struct page **pages, unsigned int gup_flags);
 
 int get_user_pages_fast(unsigned long start, int nr_pages,
                        unsigned int gup_flags, struct page **pages);
diff --git a/mm/gup.c b/mm/gup.c
index 87a6a59fe667..8ae5d09adb6b 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2030,6 +2030,12 @@ long get_user_pages_unlocked(unsigned long start, 
unsigned long nr_pages,
         */
        if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM))
                return -EINVAL;
+       /*
+        * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
+        * never directly by the caller, so enforce that:
+        */
+       if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
+               return -EINVAL;
 
        down_read(&mm->mmap_sem);
        ret = __get_user_pages_locked(current, mm, start, nr_pages, pages, NULL,
@@ -2939,3 +2945,20 @@ long pin_user_pages(unsigned long start, unsigned long 
nr_pages,
                                     pages, vmas, gup_flags);
 }
 EXPORT_SYMBOL(pin_user_pages);
+
+/*
+ * pin_user_pages_unlocked() is the FOLL_PIN variant of
+ * get_user_pages_unlocked(). Behavior is the same, except that this one sets
+ * FOLL_PIN and rejects FOLL_GET.
+ */
+long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
+                            struct page **pages, unsigned int gup_flags)
+{
+       /* FOLL_GET and FOLL_PIN are mutually exclusive. */
+       if (WARN_ON_ONCE(gup_flags & FOLL_GET))
+               return -EINVAL;
+
+       gup_flags |= FOLL_PIN;
+       return get_user_pages_unlocked(start, nr_pages, pages, gup_flags);
+}
+EXPORT_SYMBOL(pin_user_pages_unlocked);
-- 
2.26.2