This fixes a bug in changeset 22526:7a5ee3800417, where the wrong

This fixes a bug in changeset 22526:7a5ee3800417, where the wrong
value is read when deciding whether to flush the VTd tables.  The
effect is minor: in situations where the p2m entry is changed but the
mfn is the same, the VTd tables will be unnecessarily flushed.

old_entry is left untouched in the second case, since having a present
old_entry will cause the an unnecessary check to be taken at the end
of the function.

Spotted-by: Zhang, Peng Fei <zpfalpc23@gmail.com>
Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>
Acked-by: Tim Deegan <Tim.Deegan@citrix.com>