From: Jason Gunthorpe <jgg@xxxxxxxxxxxx> 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@xxxxxxxxxxxx/ I'm looking for some more acks, reviews and tests so this can move ahead to hmm.git. Detailed notes on the v2 changes are in each patch. The big changes: - mmget is held so long as the range is registered - the last patch 'Remove confusing comment and logic from hmm_release' is new Thanks everyone, Jason Jason Gunthorpe (11): 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 drivers/gpu/drm/nouveau/nouveau_svm.c | 2 +- include/linux/hmm.h | 49 +------ kernel/fork.c | 1 - mm/hmm.c | 204 ++++++++++---------------- 4 files changed, 87 insertions(+), 169 deletions(-) -- 2.21.0
