rapidio: convert get_user_pages() --> pin_user_pages()

This code was using get_user_pages_fast(), in a "Case 2" scenario
(DMA/RDMA), using the categorization from [1].  That means that it's time
to convert the get_user_pages_fast() + put_page() calls to
pin_user_pages_fast() + 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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Matt Porter <mporter@kernel.crashing.org>
Cc: Alexandre Bounine <alex.bou9@gmail.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Link: http://lkml.kernel.org/r/20200517235620.205225-3-jhubbard@nvidia.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/rapidio/devices/rio_mport_cdev.c

@@ -572,14 +572,12 @@ static void dma_req_free(struct kref *ref)
 	struct mport_dma_req *req = container_of(ref, struct mport_dma_req,
 			refcount);
 	struct mport_cdev_priv *priv = req->priv;
-	unsigned int i;
 
 	dma_unmap_sg(req->dmach->device->dev,
 		     req->sgt.sgl, req->sgt.nents, req->dir);
 	sg_free_table(&req->sgt);
 	if (req->page_list) {
-		for (i = 0; i < req->nr_pages; i++)
-			put_page(req->page_list[i]);
+		unpin_user_pages(req->page_list, req->nr_pages);
 		kfree(req->page_list);
 	}
 
@@ -815,7 +813,7 @@ rio_dma_transfer(struct file *filp, u32 transfer_mode,
 	struct mport_dma_req *req;
 	struct mport_dev *md = priv->md;
 	struct dma_chan *chan;
-	int i, ret;
+	int ret;
 	int nents;
 
 	if (xfer->length == 0)
@@ -862,7 +860,7 @@ rio_dma_transfer(struct file *filp, u32 transfer_mode,
 			goto err_req;
 		}
 
-		pinned = get_user_pages_fast(
+		pinned = pin_user_pages_fast(
 				(unsigned long)xfer->loc_addr & PAGE_MASK,
 				nr_pages,
 				dir == DMA_FROM_DEVICE ? FOLL_WRITE : 0,
@@ -870,7 +868,7 @@ rio_dma_transfer(struct file *filp, u32 transfer_mode,
 
 		if (pinned != nr_pages) {
 			if (pinned < 0) {
-				rmcd_error("get_user_pages_unlocked err=%ld",
+				rmcd_error("pin_user_pages_fast err=%ld",
 					   pinned);
 				nr_pages = 0;
 			} else
@@ -951,8 +949,7 @@ rio_dma_transfer(struct file *filp, u32 transfer_mode,
 
 err_pg:
 	if (!req->page_list) {
-		for (i = 0; i < nr_pages; i++)
-			put_page(page_list[i]);
+		unpin_user_pages(page_list, nr_pages);
 		kfree(page_list);
 	}
 err_req: