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

This code was using get_user_pages*(), 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/

Cc: Frank Haverkamp <haver@linux.ibm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Link: https://lore.kernel.org/r/20200518015237.1568940-1-jhubbard@nvidia.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/genwqe/card_utils.c

@@ -514,30 +514,6 @@ int genwqe_free_sync_sgl(struct genwqe_dev *cd, struct genwqe_sgl *sgl)
 	return rc;
 }
 
-/**
- * genwqe_free_user_pages() - Give pinned pages back
- *
- * Documentation of get_user_pages is in mm/gup.c:
- *
- * If the page is written to, set_page_dirty (or set_page_dirty_lock,
- * as appropriate) must be called after the page is finished with, and
- * before put_page is called.
- */
-static int genwqe_free_user_pages(struct page **page_list,
-			unsigned int nr_pages, int dirty)
-{
-	unsigned int i;
-
-	for (i = 0; i < nr_pages; i++) {
-		if (page_list[i] != NULL) {
-			if (dirty)
-				set_page_dirty_lock(page_list[i]);
-			put_page(page_list[i]);
-		}
-	}
-	return 0;
-}
-
 /**
  * genwqe_user_vmap() - Map user-space memory to virtual kernel memory
  * @cd:         pointer to genwqe device
@@ -597,18 +573,18 @@ int genwqe_user_vmap(struct genwqe_dev *cd, struct dma_mapping *m, void *uaddr,
 	m->dma_list = (dma_addr_t *)(m->page_list + m->nr_pages);
 
 	/* pin user pages in memory */
-	rc = get_user_pages_fast(data & PAGE_MASK, /* page aligned addr */
+	rc = pin_user_pages_fast(data & PAGE_MASK, /* page aligned addr */
 				 m->nr_pages,
 				 m->write ? FOLL_WRITE : 0,	/* readable/writable */
 				 m->page_list);	/* ptrs to pages */
 	if (rc < 0)
-		goto fail_get_user_pages;
+		goto fail_pin_user_pages;
 
-	/* assumption: get_user_pages can be killed by signals. */
+	/* assumption: pin_user_pages can be killed by signals. */
 	if (rc < m->nr_pages) {
-		genwqe_free_user_pages(m->page_list, rc, m->write);
+		unpin_user_pages_dirty_lock(m->page_list, rc, m->write);
 		rc = -EFAULT;
-		goto fail_get_user_pages;
+		goto fail_pin_user_pages;
 	}
 
 	rc = genwqe_map_pages(cd, m->page_list, m->nr_pages, m->dma_list);
@@ -618,9 +594,9 @@ int genwqe_user_vmap(struct genwqe_dev *cd, struct dma_mapping *m, void *uaddr,
 	return 0;
 
  fail_free_user_pages:
-	genwqe_free_user_pages(m->page_list, m->nr_pages, m->write);
+	unpin_user_pages_dirty_lock(m->page_list, m->nr_pages, m->write);
 
- fail_get_user_pages:
+ fail_pin_user_pages:
 	kfree(m->page_list);
 	m->page_list = NULL;
 	m->dma_list = NULL;
@@ -650,8 +626,8 @@ int genwqe_user_vunmap(struct genwqe_dev *cd, struct dma_mapping *m)
 		genwqe_unmap_pages(cd, m->dma_list, m->nr_pages);
 
 	if (m->page_list) {
-		genwqe_free_user_pages(m->page_list, m->nr_pages, m->write);
-
+		unpin_user_pages_dirty_lock(m->page_list, m->nr_pages,
+					    m->write);
 		kfree(m->page_list);
 		m->page_list = NULL;
 		m->dma_list = NULL;