Re: [PATCH v4 hmm 00/12]

[Jason Gunthorpe <jgg@mellanox.com>]

On Mon, Jun 24, 2019 at 06:00:58PM -0300, Jason Gunthorpe wrote:
> From: Jason Gunthorpe <jgg@mellanox.com>
> 
> 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().
> 
> The use of 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.
> 
> I'll apply this in the next few days - the only patch that doesn't have enough
> Reviewed-bys is 'mm/hmm: Remove confusing comment and logic from hmm_release',
> which had alot of questions, I still think it is good. If people really don't
> like it I'll drop it.
> 
> Thanks to everyone who took time to look at this!
> 
> Jason Gunthorpe (12):
>   mm/hmm: fix use after free with struct hmm in the mmu notifiers
>   mm/hmm: Use hmm_mirror not mm as an argument for hmm_range_register
>   mm/hmm: Hold a mmgrab from hmm to mm
>   mm/hmm: Simplify hmm_get_or_create and make it reliable
>   mm/hmm: Remove duplicate condition test before wait_event_timeout
>   mm/hmm: Do not use list*_rcu() for hmm->ranges
>   mm/hmm: Hold on to the mmget for the lifetime of the range
>   mm/hmm: Use lockdep instead of comments
>   mm/hmm: Remove racy protection against double-unregistration
>   mm/hmm: Poison hmm_range during unregister
>   mm/hmm: Remove confusing comment and logic from hmm_release
>   mm/hmm: Fix error flows in hmm_invalidate_range_start

I think we are done now, so applied to hmm.git, thank you to everyone.

I expect some conflicts in linux-next with the AMD DRM driver, we need
to decide how to handle them.

Jason
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