migrate_pages.2: Document EFAULT and EINVAL errors

I encountered these errors while writing testcase for migrate_pages
syscall for LTP (Linux test project).

I checked stable kernel tree 3.5 to see which paths return these.
Both can be returned from get_nodes(), which is called from:
SYSCALL_DEFINE4(migrate_pages, pid_t, pid, unsigned long, maxnode,
                const unsigned long __user *, old_nodes,
                const unsigned long __user *, new_nodes)

The testcase does following:
EFAULT
a) old_nodes/new_nodes is area mmaped with PROT_NONE
b) old_nodes/new_nodes is area not mmapped in process address
   space, -1 or area that has been just munmmaped

EINVAL
a) maxnodes overflows kernel limit
b) new_nodes contain node, which has no memory or does not exist
   or is not returned for get_mempolicy(MPOL_F_MEMS_ALLOWED).

Signed-off-by: Jan Stancek <jstancek@redhat.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/migrate_pages.2

@@ -95,6 +95,30 @@ On error, it returns \-1, and sets
 to indicate the error.
 .SH ERRORS
 .TP
+.B EFAULT
+Part or all of the memory range specified by
+.IR old_nodes / new_nodes
+and
+.I maxnode
+points outside your accessible address space.
+.TP
+.B EINVAL
+The value specified by
+.I maxnode
+exceeds a kernel-imposed limit.
+.\" As at 3.5, this limit is "a page worth of bits", e.g.,
+.\" 8 * 4096 bits, assuming a 4kB page size.
+Or,
+.I old_nodes
+or
+.I new_nodes
+specifies one or more node IDs that are
+greater than the maximum supported node ID.
+Or, none of the node IDs specified by
+.I new_nodes
+are on-line and allowed by the process's current cpuset context,
+or none of the specified nodes contain memory.
+.TP
 .B EPERM
 Insufficient privilege
 .RB ( CAP_SYS_NICE )