On 19/09/2018 18:57, Sebastian Andrzej Siewior wrote: > On 2018-09-19 07:55:51 [+0200], Paolo Bonzini wrote: >> A kthread can do use_mm/unuse_mm. > > indeed. The FPU struct for the kernel thread isn't valid / does not > contain the expected PKRU value. So loading the pkru value from the > struct FPU does not work as expected. We could set it to 0 for a kernel > thread so we don't end up with a random value. > If we want to get this usecase working then we would have to move pkru > value from FPU to mm_struct and consider it in use_mm(). Do we want > this? As a start, I think keeping it in the FPU struct but loading it unconditionally will work. kthreads will not obey PKU but it will be better already. I honestly don't know if PKRU should be per-mm, I don't know mm very well despite my brilliant observation above. :) Paolo
