xen: use vma_pages().

Replace explicit computation of vma page count by a call to
vma_pages().
Signed-off-by: Muhammad Falak R Wani <falakreyaz@gmail.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

drivers/xen/gntalloc.c

@@ -504,7 +504,7 @@ static int gntalloc_mmap(struct file *filp, struct vm_area_struct *vma)
 	struct gntalloc_file_private_data *priv = filp->private_data;
 	struct gntalloc_vma_private_data *vm_priv;
 	struct gntalloc_gref *gref;
-	int count = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
+	int count = vma_pages(vma);
 	int rv, i;
 
 	if (!(vma->vm_flags & VM_SHARED)) {

drivers/xen/gntdev.c

@@ -982,7 +982,7 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
 {
 	struct gntdev_priv *priv = flip->private_data;
 	int index = vma->vm_pgoff;
-	int count = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
+	int count = vma_pages(vma);
 	struct grant_map *map;
 	int i, err = -EINVAL;
 

drivers/xen/privcmd.c

@@ -582,7 +582,7 @@ static long privcmd_ioctl(struct file *file,
 static void privcmd_close(struct vm_area_struct *vma)
 {
 	struct page **pages = vma->vm_private_data;
-	int numpgs = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
+	int numpgs = vma_pages(vma);
 	int numgfns = (vma->vm_end - vma->vm_start) >> XEN_PAGE_SHIFT;
 	int rc;