[$] 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 remotely
by James Gowans and David Woodhouse. It was titled "user-space control of
memory mappings", with a subtitle of "letting guest memory and state
survive kexec". Some options were discussed, but the real work is clearly
yet to be done.