search for: __alloc_xen_heap_pages

Hi all, Can some one tell me where phys_to_machine_mapping is being initialized for a domU having paging mode set to PG_translate. I see that, populate_physmap() after calling __alloc_xen_heap_pages only updates the machine_to_physmap but how is the mfn for the allocated page being updated/set for phys_to_machine_mapping?? I see that phys_to_machine_mapping is a #defined to RO_MPT_VIRT_START which inturn is defined as PML4_ADDR(256).. what is this?? i have completely lose track from here on...