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From:   John Hubbard <jhubbard@nvidia.com>
To:     Andrew Morton <akpm@linux-foundation.org>
CC:     David Hildenbrand <david@redhat.com>,
        Pankaj Gupta <pankaj.gupta.linux@gmail.com>,
        Souptick Joarder <jrdr.linux@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
        John Hubbard <jhubbard@nvidia.com>
Subject: [PATCH v2 1/2] mm/gup: introduce pin_user_pages_locked()
Date:   Sun, 31 May 2020 16:41:30 -0700
Message-ID: <20200531234131.770697-2-jhubbard@nvidia.com>
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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 lon=
g 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, unsi=
gned 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;
=20
 	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, un=
signed 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_locke=
d().
+ * 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 |=3D 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);
+
--=20
2.26.2