powerpc checkpoint/restart kernel support

Patches 1-3 fix general issues and can be applied immediately.

Patches 4-8 implement the checkpoint and restart syscalls and
architecture callbacks.

Patch 9 implements the clone_with_pids syscall, but I think the shape
of that interface is yet to be finalized, so I guess it's FYI for now.

Simple single task checkpoint and restart work, as does
clone_with_pids, apparently.  Multiple task restart fails; the
coordinator task appears to be receiving a signal during
wait_all_tasks_finish() -> wait_for_completion_interruptible() for
some reason I am still trying to tracking down.

Nathan Lynch (9):
  checkpoint: fix integer-pointer conversion warnings
  fix trivial build breaks in compat code
  futex.h: fix compat builds
  powerpc: reserve checkpoint arch identifiers
  powerpc: provide APIs for validating and updating DABR
  powerpc: checkpoint/restart implementation
  powerpc: wire up checkpoint and restart syscalls
  powerpc: enable checkpoint support in Kconfig
  powerpc: clone_with_pids implementation

 arch/powerpc/Kconfig                      |    3 +
 arch/powerpc/include/asm/Kbuild           |    1 +
 arch/powerpc/include/asm/checkpoint_hdr.h |   22 ++
 arch/powerpc/include/asm/ptrace.h         |    7 +
 arch/powerpc/include/asm/syscalls.h       |    4 +
 arch/powerpc/include/asm/systbl.h         |    3 +
 arch/powerpc/include/asm/unistd.h         |    5 +-
 arch/powerpc/kernel/entry_32.S            |    8 +
 arch/powerpc/kernel/entry_64.S            |    5 +
 arch/powerpc/kernel/process.c             |   18 +
 arch/powerpc/kernel/ptrace.c              |   88 ++++--
 arch/powerpc/mm/Makefile                  |    1 +
 arch/powerpc/mm/checkpoint.c              |  531 +++++++++++++++++++++++++++++
 checkpoint/process.c                      |   14 +-
 include/linux/checkpoint_hdr.h            |    2 +
 include/linux/futex.h                     |    4 +
 16 files changed, 679 insertions(+), 37 deletions(-)
 create mode 100644 arch/powerpc/include/asm/checkpoint_hdr.h
 create mode 100644 arch/powerpc/mm/checkpoint.c