My point was that very few need more than 48 bits of virtual address space. Having extra layer of lookup will reduce page walk performance. 52-bit physical & 5

My point was that very few need more than 48 bits of virtual address space. Having extra layer of lookup will reduce page walk performance. 52-bit physical & 57-bit virtual address space is a no brainer if you have more than 128 TB of RAM installed, of course. :-)