libvirt users - Mar 2014 - virsh attach-disk live guest problem

Hypervisor= ubuntu 12.04.2
guest = ubuntu 12.04.4

used virt-manager to create a new storage file in qcow2 format on hypervisor and
then attach it to the guest.

In virt-man I can see the disk is attached.
trying virsh attach-disk I get a failure saying disk already attached
virsh dump xml shows the disk at vdb as it should be

but
on the guest, fdisk -l shows no vdb and its not in /proc

I found one reference to apparmor saying add /proc rw to hypervisor's
apparmor libvirt conf

But I see some release notes that might be about avoiding this ( sounds
insecure)

so... Do I have to stop and restart the guest, change apparmor or what?

-- 
John Fisher

I see that adding
modprobe acpiphp and  pci_hotplug
may solve the problem for Debian distros.

-- 
John Fisher