[PATCH v4 4/5] udmabuf: Pin the pages using pin_user_pages_fd() API (v3)

[Vivek Kasireddy]

Using pin_user_pages_fd() will ensure that the pages are pinned
correctly using FOLL_PIN. And, this also ensures that we don't
accidentally break features such as memory hotunplug as it would
not allow pinning pages in the movable zone.

Using this new API also simplifies the code as we no longer have
to deal with extracting individual pages from their mappings. As
a result, we can drop some of the local variables such as page,
hpage, mapping, etc.

v2:
- Adjust to the change in signature of pin_user_pages_fd() by
  passing in file * instead of fd.

v3:
- Limit the changes in this patch only to those that are required
  for using pin_user_pages_fd()
- Slightly improve the commit message

Cc: David Hildenbrand <david at redhat.com>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Mike Kravetz <mike.kravetz at oracle.com>
Cc: Hugh Dickins <hughd at google.com>
Cc: Peter Xu <peterx at redhat.com>
Cc: Jason Gunthorpe <jgg at nvidia.com>
Cc: Gerd Hoffmann <kraxel at redhat.com>
Cc: Dongwon Kim <dongwon.kim at intel.com>
Cc: Junxiao Chang <junxiao.chang at intel.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy at intel.com>
---
 drivers/dma-buf/udmabuf.c | 59 +++++++++++++++------------------------
 1 file changed, 22 insertions(+), 37 deletions(-)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index 1a41c4a069ea..883bd97e4076 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -156,7 +156,8 @@ static void release_udmabuf(struct dma_buf *buf)
 		put_sg_table(dev, ubuf->sg, DMA_BIDIRECTIONAL);
 
 	for (pg = 0; pg < ubuf->pagecount; pg++)
-		put_page(ubuf->pages[pg]);
+		unpin_user_page(ubuf->pages[pg]);
+
 	kfree(ubuf->subpgoff);
 	kfree(ubuf->pages);
 	kfree(ubuf);
@@ -217,14 +218,13 @@ static long udmabuf_create(struct miscdevice *device,
 {
 	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
 	struct file *memfd = NULL;
-	struct address_space *mapping = NULL;
 	struct udmabuf *ubuf;
 	struct dma_buf *buf;
-	pgoff_t pgoff, pgcnt, pgidx, pgbuf = 0, pglimit;
-	struct page *page, *hpage = NULL;
+	pgoff_t pgcnt, pgbuf = 0, pglimit, nr_pages;
 	pgoff_t mapidx, chunkoff, maxchunks;
 	struct hstate *hpstate;
-	int seals, ret = -EINVAL;
+	long ret = -EINVAL;
+	int seals;
 	u32 i, flags;
 
 	ubuf = kzalloc(sizeof(*ubuf), GFP_KERNEL);
@@ -258,8 +258,7 @@ static long udmabuf_create(struct miscdevice *device,
 		memfd = fget(list[i].memfd);
 		if (!memfd)
 			goto err;
-		mapping = memfd->f_mapping;
-		if (!shmem_mapping(mapping) && !is_file_hugepages(memfd))
+		if (!shmem_file(memfd) && !is_file_hugepages(memfd))
 			goto err;
 		seals = memfd_fcntl(memfd, F_GET_SEALS, 0);
 		if (seals == -EINVAL)
@@ -268,7 +267,7 @@ static long udmabuf_create(struct miscdevice *device,
 		if ((seals & SEALS_WANTED) != SEALS_WANTED ||
 		    (seals & SEALS_DENIED) != 0)
 			goto err;
-		pgoff = list[i].offset >> PAGE_SHIFT;
+		mapidx = list[i].offset >> PAGE_SHIFT;
 		pgcnt = list[i].size   >> PAGE_SHIFT;
 		if (is_file_hugepages(memfd)) {
 			if (!ubuf->subpgoff) {
@@ -286,41 +285,26 @@ static long udmabuf_create(struct miscdevice *device,
 				    ~huge_page_mask(hpstate)) >> PAGE_SHIFT;
 			maxchunks = huge_page_size(hpstate) >> PAGE_SHIFT;
 		}
-		for (pgidx = 0; pgidx < pgcnt; pgidx++) {
+
+		do {
+			nr_pages = shmem_file(memfd) ? pgcnt : 1;
+			ret = pin_user_pages_fd(memfd, mapidx, nr_pages,
+						ubuf->pages + pgbuf);
+			if (ret < 0)
+				goto err;
+
 			if (is_file_hugepages(memfd)) {
-				if (!hpage) {
-					hpage = find_get_page_flags(mapping, mapidx,
-								    FGP_ACCESSED);
-					if (!hpage) {
-						ret = -EINVAL;
-						goto err;
-					}
-				}
-				get_page(hpage);
-				ubuf->pages[pgbuf] = hpage;
-				ubuf->subpgoff[pgbuf++] = chunkoff << PAGE_SHIFT;
+				ubuf->subpgoff[pgbuf] = chunkoff << PAGE_SHIFT;
 				if (++chunkoff == maxchunks) {
-					put_page(hpage);
-					hpage = NULL;
 					chunkoff = 0;
 					mapidx++;
 				}
-			} else {
-				mapidx = pgoff + pgidx;
-				page = shmem_read_mapping_page(mapping, mapidx);
-				if (IS_ERR(page)) {
-					ret = PTR_ERR(page);
-					goto err;
-				}
-				ubuf->pages[pgbuf++] = page;
 			}
-		}
+			pgbuf += nr_pages;
+			pgcnt -= nr_pages;
+		} while (pgcnt > 0);
 		fput(memfd);
 		memfd = NULL;
-		if (hpage) {
-			put_page(hpage);
-			hpage = NULL;
-		}
 	}
 
 	exp_info.ops  = &udmabuf_ops;
@@ -341,8 +325,9 @@ static long udmabuf_create(struct miscdevice *device,
 	return dma_buf_fd(buf, flags);
 
 err:
-	while (pgbuf > 0)
-		put_page(ubuf->pages[--pgbuf]);
+	while (pgbuf-- > 0)
+		if (ubuf->pages[pgbuf])
+			unpin_user_page(ubuf->pages[pgbuf]);
 	if (memfd)
 		fput(memfd);
 	kfree(ubuf->subpgoff);
-- 
2.39.2