[PATCH v3 hmm 00/12] mm/hmm: Various revisions from a locking/code review

Jason Gunthorpe jgg at ziepe.ca
Fri Jun 14 00:44:38 UTC 2019

From: Jason Gunthorpe <jgg at 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 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 would like to run some testing with the ODP patch, but haven't
yet. Otherwise I think this is reviewed enough, and if there is nothing more
say I hope to apply it next week.

I plan to continue to work on the idea with CH to move more of this mirror
code into mmu notifiers and other places, but this will take some time and

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: 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: Do not use list*_rcu() for hmm->ranges
  mm/hmm: Remove confusing comment and logic from hmm_release
  mm/hmm: Fix error flows in hmm_invalidate_range_start

 drivers/gpu/drm/nouveau/nouveau_svm.c |   2 +-
 include/linux/hmm.h                   |  52 +----
 kernel/fork.c                         |   1 -
 mm/hmm.c                              | 286 ++++++++++++--------------
 4 files changed, 140 insertions(+), 201 deletions(-)


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