Re: [PATCH hmm 00/15] Consolidate the mmu notifier interval_tree and locking

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

Am 15.10.19 um 20:12 schrieb Jason Gunthorpe:
> From: Jason Gunthorpe <jgg@mellanox.com>
>
> 8 of the mmu_notifier using drivers (i915_gem, radeon_mn, umem_odp, hfi1,
> scif_dma, vhost, gntdev, hmm) drivers are using a common pattern where
> they only use invalidate_range_start/end and immediately check the
> invalidating range against some driver data structure to tell if the
> driver is interested. Half of them use an interval_tree, the others are
> simple linear search lists.
>
> Of the ones I checked they largely seem to have various kinds of races,
> bugs and poor implementation. This is a result of the complexity in how
> the notifier interacts with get_user_pages(). It is extremely difficult to
> use it correctly.
>
> Consolidate all of this code together into the core mmu_notifier and
> provide a locking scheme similar to hmm_mirror that allows the user to
> safely use get_user_pages() and reliably know if the page list still
> matches the mm.

That sounds really good, but could you outline for a moment how that is 
archived?

Please keep in mind that the page reference get_user_pages() grabs is 
*NOT* sufficient to guarantee coherency here.

Regards,
Christian.

>
> This new arrangment plays nicely with the !blockable mode for
> OOM. Scanning the interval tree is done such that the intersection test
> will always succeed, and since there is no invalidate_range_end exposed to
> drivers the scheme safely allows multiple drivers to be subscribed.
>
> Four places are converted as an example of how the new API is used.
> Four are left for future patches:
>   - i915_gem has complex locking around destruction of a registration,
>     needs more study
>   - hfi1 (2nd user) needs access to the rbtree
>   - scif_dma has a complicated logic flow
>   - vhost's mmu notifiers are already being rewritten
>
> This is still being tested, but I figured to send it to start getting help
> from the xen, amd and hfi drivers which I cannot test here.
>
> It would be intended for the hmm tree.
>
> Jason Gunthorpe (15):
>    mm/mmu_notifier: define the header pre-processor parts even if
>      disabled
>    mm/mmu_notifier: add an interval tree notifier
>    mm/hmm: allow hmm_range to be used with a mmu_range_notifier or
>      hmm_mirror
>    mm/hmm: define the pre-processor related parts of hmm.h even if
>      disabled
>    RDMA/odp: Use mmu_range_notifier_insert()
>    RDMA/hfi1: Use mmu_range_notifier_inset for user_exp_rcv
>    drm/radeon: use mmu_range_notifier_insert
>    xen/gntdev: Use select for DMA_SHARED_BUFFER
>    xen/gntdev: use mmu_range_notifier_insert
>    nouveau: use mmu_notifier directly for invalidate_range_start
>    nouveau: use mmu_range_notifier instead of hmm_mirror
>    drm/amdgpu: Call find_vma under mmap_sem
>    drm/amdgpu: Use mmu_range_insert instead of hmm_mirror
>    drm/amdgpu: Use mmu_range_notifier instead of hmm_mirror
>    mm/hmm: remove hmm_mirror and related
>
>   Documentation/vm/hmm.rst                      | 105 +---
>   drivers/gpu/drm/amd/amdgpu/amdgpu.h           |   2 +
>   .../gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c  |   9 +-
>   drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c        |  14 +-
>   drivers/gpu/drm/amd/amdgpu/amdgpu_device.c    |   1 +
>   drivers/gpu/drm/amd/amdgpu/amdgpu_mn.c        | 445 ++------------
>   drivers/gpu/drm/amd/amdgpu/amdgpu_mn.h        |  53 --
>   drivers/gpu/drm/amd/amdgpu/amdgpu_object.h    |  13 +-
>   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c       | 111 ++--
>   drivers/gpu/drm/nouveau/nouveau_svm.c         | 229 +++++---
>   drivers/gpu/drm/radeon/radeon.h               |   9 +-
>   drivers/gpu/drm/radeon/radeon_mn.c            | 218 ++-----
>   drivers/infiniband/core/device.c              |   1 -
>   drivers/infiniband/core/umem_odp.c            | 288 +---------
>   drivers/infiniband/hw/hfi1/file_ops.c         |   2 +-
>   drivers/infiniband/hw/hfi1/hfi.h              |   2 +-
>   drivers/infiniband/hw/hfi1/user_exp_rcv.c     | 144 ++---
>   drivers/infiniband/hw/hfi1/user_exp_rcv.h     |   3 +-
>   drivers/infiniband/hw/mlx5/mlx5_ib.h          |   7 +-
>   drivers/infiniband/hw/mlx5/mr.c               |   3 +-
>   drivers/infiniband/hw/mlx5/odp.c              |  48 +-
>   drivers/xen/Kconfig                           |   3 +-
>   drivers/xen/gntdev-common.h                   |   8 +-
>   drivers/xen/gntdev.c                          | 179 ++----
>   include/linux/hmm.h                           | 195 +------
>   include/linux/mmu_notifier.h                  | 124 +++-
>   include/rdma/ib_umem_odp.h                    |  65 +--
>   include/rdma/ib_verbs.h                       |   2 -
>   kernel/fork.c                                 |   1 -
>   mm/Kconfig                                    |   2 +-
>   mm/hmm.c                                      | 275 +--------
>   mm/mmu_notifier.c                             | 542 +++++++++++++++++-
>   32 files changed, 1180 insertions(+), 1923 deletions(-)
>