After system bootup, there is no totally reliable way to see
which CPUs are isolated, because the kernel may modify the
CPUs specified on the isolcpus= kernel command line option.

Export the CPU list that actually got isolated in sysfs,
specifically in the file /sys/devices/system/cpu/isolated

This can be used by system management tools like libvirt,
openstack, and others to ensure proper placement of tasks.
Suggested-by: NLi Zefan <lizefan@huawei.com>
Signed-off-by: NRik van Riel <riel@redhat.com>
Acked-by: NMike Galbraith <umgwanakikbuti@gmail.com>
Acked-by: NChris Metcalf <cmetcalf@ezchip.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>