Why should we have self-unmapping code in parasite?
It looks like, we can drop this code using simple sys_unmap()
injection (like that I did for `criu exec` action and for cases where we
failed to insert parasite by some reason, but still need to unmap remotes).

It's an RFC, so just a suggestion - maybe I miss something you have in
mind - please, describe that/those things.

My motivation is:
- less code, defined commands for PIE, one BUG() less, one jump to PIE less
- I'm making one 64-bit parasite on x86 instead of two 32 and 64 bit.
  It works (branch 32-one-parasite) with long-jump in the beginning to
  64-bit code from 32-bit task.
  On parasite curing it sig-returns from 64-bit parasite to 32-bit task,
  this point we're trapping in CRIU. After that we command parasite to
  unmap itself, so it long-jumps again to parasite 64-bit code, unmaps,
  we caught task after sys_unmap and the task is with 64-bit CS.
  We can't set 32-bit registers after this - kernel checks that
  registers set is the same on PTRACE_SETREGSET:
> > static int ptrace_regset(struct task_struct *task, int req, unsigned int type,
> >                        struct iovec *kiov)
...
> >       if (!regset || (kiov->iov_len % regset->size) != 0)
> >               return -EINVAL;
  So, to return again to 32-bit task I need sigreturn() again or add
  long-jump with 32-bit CS.
  I've disable that for 32-bit testing with (in compel_cure_remote):
-       if (ctl->addr_cmd) {
+       if (ctl->addr_cmd && user_regs_native(&ctl->orig.regs)) {
  And it works. It also works for native tasks, so why should we keep it?

travis-ci: success for compel: kill self-unmap in parasite
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Pavel Emelyanov <xemul@virtuozzo.com>
Cc: Andrei Vagin <avagin@virtuozzo.com>
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Acked-by: Andrei Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>