xen/gntdev.c: convert to use vm_map_pages()

Convert to use vm_map_pages() to map range of kernel memory to user vma.

map->count is passed to vm_map_pages() and internal API verify map->count
against count ( count = vma_pages(vma)) for page array boundary overrun
condition.

Link: http://lkml.kernel.org/r/88e56e82d2db98705c2d842e9c9806c00b366d67.1552921225.git.jrdr.linux@gmail.comSigned-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Heiko Stuebner <heiko@sntech.de>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mauro Carvalho Chehab <mchehab@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Cc: Pawel Osciak <pawel@osciak.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Sandy Huang <hjc@rock-chips.com>
Cc: Stefan Richter <stefanr@s5r6.in-berlin.de>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Thierry Reding <treding@nvidia.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/xen/gntdev.c

@@ -1084,7 +1084,7 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
 	int index = vma->vm_pgoff;
 	int count = vma_pages(vma);
 	struct gntdev_grant_map *map;
-	int i, err = -EINVAL;
+	int err = -EINVAL;
 
 	if ((vma->vm_flags & VM_WRITE) && !(vma->vm_flags & VM_SHARED))
 		return -EINVAL;
@@ -1145,12 +1145,9 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
 		goto out_put_map;
 
 	if (!use_ptemod) {
-		for (i = 0; i < count; i++) {
-			err = vm_insert_page(vma, vma->vm_start + i*PAGE_SIZE,
-				map->pages[i]);
+		err = vm_map_pages(vma, map->pages, map->count);
 		if (err)
 			goto out_put_map;
-		}
 	} else {
 #ifdef CONFIG_X86
 		/*