mm/mmap: use vms accounted pages in mmap_region()

Change from nr_pages variable to vms.nr_accounted for the charged pages
calculation.  This is necessary for a future patch.

This also avoids checking security_vm_enough_memory_mm() if the amount of
memory won't change.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Liam R. Howlett <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
Reviewed-by: Lorenzo Stoakes <[email protected]>
Reviewed-by: Suren Baghdasaryan <[email protected]>
Acked-by: Paul Moore <[email protected]>	[LSM]
Cc: Kees Cook <[email protected]>
Cc: Bert Karwatzki <[email protected]>
Cc: Jeff Xu <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Mark Brown <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: "Paul E. McKenney" <[email protected]>
Cc: Sidhartha Kumar <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

mm/mmap.c

@@ -1414,9 +1414,10 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 	 */
 	if (accountable_mapping(file, vm_flags)) {
 		charged = pglen;
-		charged -= nr_accounted;
-		if (security_vm_enough_memory_mm(mm, charged))
+		charged -= vms.nr_accounted;
+		if (charged && security_vm_enough_memory_mm(mm, charged))
 			goto abort_munmap;
+
 		vms.nr_accounted = 0;
 		vm_flags |= VM_ACCOUNT;
 	}