[$] Preserving guest memory across kexec

The final session in the memory-management track at the 2022 Linux Storage,Filesystem, Memory-management and BPF Summit (LSFMM) was run remotelyby James Gowans and David Woodhouse. It was titled "user-space control ofmemory mappings", with a subtitle of "letting guest memory and statesurvive kexec". Some options were discussed, but the real work is clearlyyet to be done.