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Subject[PATCH v2 1/2] mm/gup: introduce pin_user_pages_locked()
Date
Introduce pin_user_pages_locked(), which is nearly identical to
get_user_pages_locked() 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>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
include/linux/mm.h | 2 ++
mm/gup.c | 36 ++++++++++++++++++++++++++++++++++++
2 files changed, 38 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index b098939691ba..5e29ddcbb5fc 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1711,6 +1711,8 @@ long pin_user_pages(unsigned long start, unsigned long nr_pages,
struct vm_area_struct **vmas);
long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
unsigned int gup_flags, struct page **pages, int *locked);
+long pin_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,
diff --git a/mm/gup.c b/mm/gup.c
index 82ef0db1590a..06b891297a5c 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1993,6 +1993,12 @@ long get_user_pages_locked(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;

return __get_user_pages_locked(current, current->mm, start, nr_pages,
pages, NULL, locked,
@@ -2998,3 +3004,33 @@ long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
return get_user_pages_unlocked(start, nr_pages, pages, gup_flags);
}
EXPORT_SYMBOL(pin_user_pages_unlocked);
+
+/*
+ * pin_user_pages_locked() is the FOLL_PIN variant of get_user_pages_locked().
+ * Behavior is the same, except that this one sets FOLL_PIN and rejects
+ * FOLL_GET.
+ */
+long pin_user_pages_locked(unsigned long start, unsigned long nr_pages,
+ unsigned int gup_flags, struct page **pages,
+ int *locked)
+{
+ /*
+ * FIXME: Current FOLL_LONGTERM behavior is incompatible with
+ * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on
+ * vmas. As there are no users of this flag in this call we simply
+ * disallow this option for now.
+ */
+ if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM))
+ return -EINVAL;
+
+ /* 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_locked(current, current->mm, start, nr_pages,
+ pages, NULL, locked,
+ gup_flags | FOLL_TOUCH);
+}
+EXPORT_SYMBOL(pin_user_pages_locked);
+
--
2.26.2
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