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Subject[PATCH v2 1/2] mm/gup: introduce pin_user_pages_unlocked
Date
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.linux@gmail.com>
Signed-off-by: John Hubbard <jhubbard@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
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