On 5/23/19 8:34 AM, Jason Gunthorpe wrote:
From: Jason Gunthorpe <jgg@xxxxxxxxxxxx> 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. I expect Jerome & Ralph will have some design notes so this is just RFC, and it still needs a matching edit to nouveau. It is only compile tested.
Thanks so much for doing this. Jerome has already absorbed these into his hmm-5.3 branch, along with Ralph's other fixes, so we can start testing, as well as reviewing, the whole set. We'll have feedback soon. thanks, -- John Hubbard NVIDIA
