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From:   John Hubbard <jhubbard@nvidia.com>
To:     Andrew Morton <akpm@linux-foundation.org>
CC:     LKML <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
        John Hubbard <jhubbard@nvidia.com>
Subject: [PATCH 2/2] mm/gup: frame_vector: convert get_user_pages() --> pin_user_pages()
Date:   Wed, 27 May 2020 15:32:43 -0700
Message-ID: <20200527223243.884385-3-jhubbard@nvidia.com>
In-Reply-To: <20200527223243.884385-1-jhubbard@nvidia.com>
References: <20200527223243.884385-1-jhubbard@nvidia.com>
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This code was using get_user_pages*(), and all of the callers so far
were in a "Case 2" scenario (DMA/RDMA), using the categorization
from [1]. That means that it's time to convert the get_user_pages*() +
put_page() calls to pin_user_pages*() + unpin_user_pages() calls.

There is some helpful background in [2]: basically, this is a small
part of fixing a long-standing disconnect between pinning pages, and
file systems' use of those pages.

[1] Documentation/core-api/pin_user_pages.rst

[2] "Explicit pinning of user-space pages":
    https://lwn.net/Articles/807108/

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 mm/frame_vector.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/mm/frame_vector.c b/mm/frame_vector.c
index c431ca81dad5..4107dbca0056 100644
--- a/mm/frame_vector.c
+++ b/mm/frame_vector.c
@@ -72,7 +72,7 @@ int get_vaddr_frames(unsigned long start, unsigned int nr=
_frames,
 	if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
 		vec->got_ref =3D true;
 		vec->is_pfns =3D false;
-		ret =3D get_user_pages_locked(start, nr_frames,
+		ret =3D pin_user_pages_locked(start, nr_frames,
 			gup_flags, (struct page **)(vec->ptrs), &locked);
 		goto out;
 	}
@@ -122,7 +122,6 @@ EXPORT_SYMBOL(get_vaddr_frames);
  */
 void put_vaddr_frames(struct frame_vector *vec)
 {
-	int i;
 	struct page **pages;
=20
 	if (!vec->got_ref)
@@ -135,8 +134,8 @@ void put_vaddr_frames(struct frame_vector *vec)
 	 */
 	if (WARN_ON(IS_ERR(pages)))
 		goto out;
-	for (i =3D 0; i < vec->nr_frames; i++)
-		put_page(pages[i]);
+
+	unpin_user_pages(pages, vec->nr_frames);
 	vec->got_ref =3D false;
 out:
 	vec->nr_frames =3D 0;
--=20
2.26.2