xenpaging: remove confusing comment from p2m_mem_paging_populate

Currently there is no way to avoid the double check of the p2mt
because p2m_mem_paging_populate() is called from many places without
the p2m_lock held. Upcoming changes will move the function into
gfn_to_mfn(), so its interface could be changed and the extra
p2m_lock/get_entry can be removed.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Acked-by: Tim Deegan <tim@xen.org>
Committed-by: Tim Deegan <tim@xen.org>

xen/arch/x86/mm/p2m.c

@@ -792,8 +792,6 @@ void p2m_mem_paging_populate(struct domain *d, unsigned long gfn)
     req.type = MEM_EVENT_TYPE_PAGING;
 
     /* Fix p2m mapping */
-    /* XXX: It seems inefficient to have this here, as it's only needed
-     *      in one case (ept guest accessing paging out page) */
     p2m_lock(p2m);
     p2m->get_entry(p2m, gfn, &p2mt, &a, p2m_query, NULL);
     if ( p2mt == p2m_ram_paged )