Also fixes a couple of boundary cases.
Signed-off-by: NKeir Fraser <keir.fraser@citrix.com>
Signed-off-by: NIan Campbell <ian.campbell@citrix.com>
[ijc: forward ported from linux-2.6.18-xen.hg 988:c88a02a22a05]
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>