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

[Michael Ellerman]

Scott Wood <oss at buserror.net> writes:

> On Tue, 2017-05-09 at 00:09 +1000, Michael Ellerman wrote:
>> 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.
>
> Are you using a 64-bit userspace?

Ah of course. It's debian so it's mostly 32-bit. I'd forgotten 32-bit
userspace was a thing! :)

I'll fix my tests to run some 64-bit binaries.

cheers