Re: [PATCH v2 hmm 00/11] Various revisions from a locking/code review

["Kuehling, Felix" <Felix.Kuehling@amd.com>]

[+Philip]

Hi Jason,

I'm out of the office this week.

Hi Philip, can you give this a go? Not sure how much you've been 
following this patch series review. Message or call me on Skype to 
discuss any questions.

Thanks,
   Felix

On 2019-06-11 12:48, Jason Gunthorpe wrote:
> On Thu, Jun 06, 2019 at 03:44:27PM -0300, Jason Gunthorpe wrote:
>> From: Jason Gunthorpe <jgg@mellanox.com>
>>
>> For hmm.git:
>>
>> This patch series arised out of discussions with Jerome when looking at the
>> ODP changes, particularly informed by use after free races we have already
>> found and fixed in the ODP code (thanks to syzkaller) working with mmu
>> notifiers, and the discussion with Ralph on how to resolve the lifetime model.
>>
>> Overall this brings in a simplified locking scheme and easy to explain
>> lifetime model:
>>
>>   If a hmm_range is valid, then the hmm is valid, if a hmm is valid then the mm
>>   is allocated memory.
>>
>>   If the mm needs to still be alive (ie to lock the mmap_sem, find a vma, etc)
>>   then the mmget must be obtained via mmget_not_zero().
>>
>> Locking of mm->hmm is shifted to use the mmap_sem consistently for all
>> read/write and unlocked accesses are removed.
>>
>> The use unlocked reads on 'hmm->dead' are also eliminated in favour of using
>> standard mmget() locking to prevent the mm from being released. Many of the
>> debugging checks of !range->hmm and !hmm->mm are dropped in favour of poison -
>> which is much clearer as to the lifetime intent.
>>
>> The trailing patches are just some random cleanups I noticed when reviewing
>> this code.
>>
>> This v2 incorporates alot of the good off list changes & feedback Jerome had,
>> and all the on-list comments too. However, now that we have the shared git I
>> have kept the one line change to nouveau_svm.c rather than the compat
>> funtions.
>>
>> I believe we can resolve this merge in the DRM tree now and keep the core
>> mm/hmm.c clean. DRM maintainers, please correct me if I'm wrong.
>>
>> It is on top of hmm.git, and I have a git tree of this series to ease testing
>> here:
>>
>> https://github.com/jgunthorpe/linux/tree/hmm
>>
>> There are still some open locking issues, as I think this remains unaddressed:
>>
>> https://lore.kernel.org/linux-mm/20190527195829.GB18019@mellanox.com/
>>
>> I'm looking for some more acks, reviews and tests so this can move ahead to
>> hmm.git.
> AMD Folks, this is looking pretty good now, can you please give at
> least a Tested-by for the new driver code using this that I see in
> linux-next?
>
> Thanks,
> Jason