in the akaros virtual machine code, we set up a simple 1:1 map and start linux at the 64-bit entry point, at which point it builds its own page tables. So entering a payload in long mode is certainly possible and IMHO ought to be the standard on amd64 -- not that anyone cares what I think anyway :-)Anyway, I'm going to be working on replacing ramstage with linux again, so I'm not as concerted with coreboot ramstage just now ;-)