The POWER9 processor core supports a 64-bit effective address (EA), 68-bit virtual address (VA), and a 56-bit host real (physical) address (RA)

68-bit addresses!?

In HPT mode, the effective address space is 64 bits (0:63), the virtual address space is implemented as 68 bits (10:77) of the 78-bit architected maximum virtual address space, and the real address space is 51 bits (13:63).

I don’t really understand what this means.