x86/PoD: handle intermediate page orders in p2m_pod_cache_add()

x86/PoD: handle intermediate page orders in p2m_pod_cache_add()

p2m_pod_decrease_reservation() may pass pages to the function which
aren't 4k, 2M, or 1G. Handle all intermediate orders as well, to avoid
hitting the BUG() at the switch() statement's "default" case.

This is CVE-2021-28708 / part of XSA-388.

Fixes: 3c352011c0d3 ("x86/PoD: shorten certain operations on higher order ranges")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
master commit: 8ec13f68e0b026863d23e7f44f252d06478bc809
master date: 2021-11-22 12:27:30 +0000