[PATCH] powerpc/64e: Don't place the stack beyond TASK_SIZE

[Michael Ellerman]

Scott Wood <oss at buserror.net> writes:

> Commit f4ea6dcb08ea ("powerpc/mm: Enable mappings above 128TB") increased
> the task size on book3s, and introduced a mechanism to dynamically
> control whether a task uses these larger addresses.  While the change to
> the task size itself was ifdef-protected to only apply on book3s, the
> change to STACK_TOP_USER64 was not.  On book3e, this had the effect of
> trying to use addresses up to 128TiB for the stack despite a 64TiB task
> size limit -- which broke 64-bit userspace producing the following errors:
>
> Starting init: /sbin/init exists but couldn't execute it (error -14)
> Starting init: /bin/sh exists but couldn't execute it (error -14)
> Kernel panic - not syncing: No working init found.  Try passing init= option to kernel. See Linux Documentation/admin-guide/init.rst for guidance.

For some reason I am not seeing this on my p5020ds?

I just checked, it's definitely booting:

  [    0.000000] Linux version 4.11.0-gcc5-g13e0988 (kerkins at alpine1-p1) (gcc version 5.2.1 20151001 (GCC) ) #1 SMP Mon May 8 05:33:22 AEST 2017
  [    0.000000] Using CoreNet Generic machine description
  ...
  [    3.216940] systemd[1]: Detected architecture ppc64.
  ...
  Debian GNU/Linux stretch/sid p5020ds ttyS0
  
  p5020ds login:


Anyway patch looks good, I'll pull it in with the rest of your tree.

cheers