Re: [PATCH kernel 05/15] powerpc/iommu: Stop using @current in mm_iommu_xxx

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 05/08/16 17:00, Michael Ellerman wrote:
> Alexey Kardashevskiy <aik@ozlabs.ru> writes:
> 
>> In some situations the userspace memory context may live longer than
>> the userspace process itself so if we need to do proper memory context
>> cleanup, we better cache @mm and use it later when the process is gone
>> (@current or @current->mm are NULL).
>>
>> This changes mm_iommu_xxx API to receive mm_struct instead of using one
>> from @current.
>>
>> This is needed by the following patch to do proper cleanup in time.
>> This depends on "powerpc/powernv/ioda: Fix endianness when reading TCEs"
>> to do proper cleanup via tce_iommu_clear() patch.
>>
>> To keep API consistent, this replaces mm_context_t with mm_struct;
>> we stick to mm_struct as mm_iommu_adjust_locked_vm() helper needs
>> access to &mm->mmap_sem.
>>
>> This should cause no behavioral change.
> 
> Is this a theoretical bug, or do we hit it in practice?

Actual bug.

> 
> In other words, should I merge this as a fix for 4.8, or can it wait for
> 4.9 with the rest of the series?

Assuming this does not have "rb" or "ab" from anyone familiar with IOMMU on
powernv, this has to wait :-/

> 
>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
>> ---
>>  arch/powerpc/include/asm/mmu_context.h | 20 +++++++------
>>  arch/powerpc/kernel/setup-common.c     |  2 +-
>>  arch/powerpc/mm/mmu_context_book3s64.c |  4 +--
>>  arch/powerpc/mm/mmu_context_iommu.c    | 54 ++++++++++++++--------------------
> 
>>  drivers/vfio/vfio_iommu_spapr_tce.c    | 41 ++++++++++++++++----------
> 
> I'd need an ACK from Alex for that part.



-- 
Alexey