Kernel 4.15 lost set_robust_list support on POWER 9

[Benjamin Herrenschmidt]

On Mon, 2018-02-05 at 19:14 -0200, Mauricio Faria de Oliveira wrote:
> Nick, Michael,

+Aneesh.

> On 02/05/2018 10:48 AM, Florian Weimer wrote:
> > 7041  set_robust_list(0x7fff93dc3980, 24) = -1 ENOSYS (Function not 
> > implemented)
> 
> The regression was introduced by commit 371b8044 ("powerpc/64s: 
> Initialize ISAv3 MMU registers before setting partition table").
> 
> The problem is Radix MMU specific (does not occur with 'disable_radix'),
> and does not occur with that code reverted (ie do not set PIDR to zero).
> 
> Do you see any reasons why?
> (wondering if at all related to access_ok() in include/asm/uaccess.h)
> 
> with:
> 
>      # strace -e set_robust_list -f ./test
>      set_robust_list(0x7fffa4b03910, 24)     = -1 ENOSYS (Function not 
> implemented)
>      +++ exited with 1 +++
> 
>      # uname -r
>      4.15.0
> 
> without:
> 
>      # strace -e set_robust_list -f ./test
>      set_robust_list(0x7fff889c3910, 24)     = 0
>      +++ exited with 0 +++
> 
>      # uname -r
>      4.15.0.nopidr