x86/P2M: deal with partial success of p2m_set_entry()

x86/P2M: deal with partial success of p2m_set_entry()

M2P and PoD stats need to remain in sync with P2M; if an update succeeds
only partially, respective adjustments need to be made. If updates get
made before the call, they may also need undoing upon complete failure
(i.e. including the single-page case).

Log-dirty state would better also be kept in sync.

Note that the change to set_typed_p2m_entry() may not be strictly
necessary (due to the order restriction enforced near the top of the
function), but is being kept here to be on the safe side.

This is CVE-2021-28705 and CVE-2021-28709 / XSA-389.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>