[WallWextra]

This could be done mostly transparently, with the encryption in the memory controller. Addresses and data are already scrambled with a (non-cryptographic) scrambling code for EMI reasons. Of course, a sufficiently fast hardware crypto core would be required.

EDIT: Also, I forgot that the last generation of consoles (and I assume the current) have transparent encryption of main memory.

[justincormack]

Indeed, there is discussion of encrypted memory on the controller in Risc-V at http://lowrisc.org