RE: [RFC PATCH v2 0/3] RDMA: add dma-buf support

["Xiong, Jianxin" <jianxin.xiong@intel.com>]

Added to cc-list:
Christian Koenig <christian.koenig@amd.com>
dri-devel@lists.freedesktop.org

> -----Original Message-----
> From: Xiong, Jianxin <jianxin.xiong@intel.com>
> Sent: Monday, June 29, 2020 10:32 AM
> To: linux-rdma@vger.kernel.org
> Cc: Xiong, Jianxin <jianxin.xiong@intel.com>; Doug Ledford <dledford@redhat.com>; Jason Gunthorpe <jgg@ziepe.ca>; Sumit Semwal
> <sumit.semwal@linaro.org>; Leon Romanovsky <leon@kernel.org>; Vetter, Daniel <daniel.vetter@intel.com>
> Subject: [RFC PATCH v2 0/3] RDMA: add dma-buf support
> 
> When enabled, an RDMA capable NIC can perform peer-to-peer transactions
> over PCIe to access the local memory located on another device. This can
> often lead to better performance than using a system memory buffer for
> RDMA and copying data between the buffer and device memory.
> 
> Current kernel RDMA stack uses get_user_pages() to pin the physical
> pages backing the user buffer and uses dma_map_sg_attrs() to get the
> dma addresses for memory access. This usually doesn't work for peer
> device memory due to the lack of associated page structures.
> 
> Several mechanisms exist today to facilitate device memory access.
> 
> ZONE_DEVICE is a new zone for device memory in the memory management
> subsystem. It allows pages from device memory being described with
> specialized page structures. As the result, calls like get_user_pages()
> can succeed, but what can be done with these page structures may be
> different from system memory. It is further specialized into multiple
> memory types, such as one type for PCI p2pmem/p2pdma and one type for
> HMM.
> 
> PCI p2pmem/p2pdma uses ZONE_DEVICE to represent device memory residing
> in a PCI BAR and provides a set of calls to publish, discover, allocate,
> and map such memory for peer-to-peer transactions. One feature of the
> API is that the buffer is allocated by the side that does the DMA
> transfer. This works well with the storage usage case, but is awkward
> with GPU-NIC communication, where typically the buffer is allocated by
> the GPU driver rather than the NIC driver.
> 
> Heterogeneous Memory Management (HMM) utilizes mmu_interval_notifier
> and ZONE_DEVICE to support shared virtual address space and page
> migration between system memory and device memory. HMM doesn't support
> pinning device memory because pages located on device must be able to
> migrate to system memory when accessed by CPU. Peer-to-peer access
> is possible if the peer can handle page fault. For RDMA, that means
> the NIC must support on-demand paging.
> 
> Dma-buf is a standard mechanism for sharing buffers among different
> device drivers. The buffer to be shared is exported by the owning
> driver and imported by the driver that wants to use it. The exporter
> provides a set of ops that the importer can call to pin and map the
> buffer. In addition, a file descriptor can be associated with a dma-
> buf object as the handle that can be passed to user space.
> 
> This patch series adds dma-buf importer role to the RDMA driver in
> attempt to support RDMA using device memory such as GPU VRAM. Dma-buf is
> chosen for a few reasons: first, the API is relatively simple and allows
> a lot of flexibility in implementing the buffer manipulation ops.
> Second, it doesn't require page structure. Third, dma-buf is already
> supported in many GPU drivers. However, we are aware that existing GPU
> drivers don't allow pinning device memory via the dma-buf interface.
> Pinning and mapping a dma-buf would cause the backing storage to migrate
> to system RAM. This is due to the lack of knowledge about whether the
> importer can perform peer-to-peer access and the lack of resource limit
> control measure for GPU. For the first part, the latest dma-buf driver
> has a peer-to-peer flag for the importer, but the flag is currently tied
> to dynamic mapping support, which requires on-demand paging support from
> the NIC to work. There are a few possible ways to address these issues,
> such as decoupling peer-to-peer flag from dynamic mapping, allowing more
> leeway for individual drivers to make the pinning decision and adding
> GPU resource limit control via cgroup. We would like to get comments on
> this patch series with the assumption that device memory pinning via
> dma-buf is supported by some GPU drivers, and at the same time welcome
> open discussions on how to address the aforementioned issues as well as
> GPU-NIC peer-to-peer access solutions in general.
> 
> This is the second version of the patch series. Here are the changes
> from the previous version:
> * The Kconfig option is removed. There is no dependence issue since
> dma-buf driver is always enabled.
> * The declaration of new data structure and functions is reorganized to
> minimize the visibility of the changes.
> * The new uverbs command now goes through ioctl() instead of write().
> * The rereg functionality is removed.
> * Instead of adding new device method for dma-buf specific registration,
> existing method is extended to accept an extra parameter.
> * The correct function is now used for address range checking.
> 
> This series is organized as follows. The first patch adds the common
> code for importing dma-buf from a file descriptor and pinning and
> mapping the dma-buf pages. Patch 2 extends the reg_user_mr() method
> of the ib_device structure to accept dma-buf file descriptor as an extra
> parameter. Vendor drivers are updated with the change. Patch 3 adds a
> new uverbs command for registering dma-buf based memory region.
> 
> Related user space RDMA library changes will be provided as a separate
> patch series.
> 
> Jianxin Xiong (3):
>   RDMA/umem: Support importing dma-buf as user memory region
>   RDMA/core: Expand the driver method 'reg_user_mr' to support dma-buf
>   RDMA/uverbs: Add uverbs command for dma-buf based MR registration
> 
>  drivers/infiniband/core/Makefile                |   2 +-
>  drivers/infiniband/core/umem.c                  |   4 +
>  drivers/infiniband/core/umem_dmabuf.c           | 105 ++++++++++++++++++++++
>  drivers/infiniband/core/umem_dmabuf.h           |  11 +++
>  drivers/infiniband/core/uverbs_cmd.c            |   2 +-
>  drivers/infiniband/core/uverbs_std_types_mr.c   | 112 ++++++++++++++++++++++++
>  drivers/infiniband/core/verbs.c                 |   2 +-
>  drivers/infiniband/hw/bnxt_re/ib_verbs.c        |   7 +-
>  drivers/infiniband/hw/bnxt_re/ib_verbs.h        |   2 +-
>  drivers/infiniband/hw/cxgb4/iw_cxgb4.h          |   3 +-
>  drivers/infiniband/hw/cxgb4/mem.c               |   8 +-
>  drivers/infiniband/hw/efa/efa.h                 |   2 +-
>  drivers/infiniband/hw/efa/efa_verbs.c           |   7 +-
>  drivers/infiniband/hw/hns/hns_roce_device.h     |   2 +-
>  drivers/infiniband/hw/hns/hns_roce_mr.c         |   7 +-
>  drivers/infiniband/hw/i40iw/i40iw_verbs.c       |   6 ++
>  drivers/infiniband/hw/mlx4/mlx4_ib.h            |   2 +-
>  drivers/infiniband/hw/mlx4/mr.c                 |   7 +-
>  drivers/infiniband/hw/mlx5/mlx5_ib.h            |   2 +-
>  drivers/infiniband/hw/mlx5/mr.c                 |  45 +++++++++-
>  drivers/infiniband/hw/mthca/mthca_provider.c    |   8 +-
>  drivers/infiniband/hw/ocrdma/ocrdma_verbs.c     |   9 +-
>  drivers/infiniband/hw/ocrdma/ocrdma_verbs.h     |   3 +-
>  drivers/infiniband/hw/qedr/verbs.c              |   8 +-
>  drivers/infiniband/hw/qedr/verbs.h              |   3 +-
>  drivers/infiniband/hw/usnic/usnic_ib_verbs.c    |   8 +-
>  drivers/infiniband/hw/usnic/usnic_ib_verbs.h    |   2 +-
>  drivers/infiniband/hw/vmw_pvrdma/pvrdma_mr.c    |   6 +-
>  drivers/infiniband/hw/vmw_pvrdma/pvrdma_verbs.h |   2 +-
>  drivers/infiniband/sw/rdmavt/mr.c               |   6 +-
>  drivers/infiniband/sw/rdmavt/mr.h               |   2 +-
>  drivers/infiniband/sw/rxe/rxe_verbs.c           |   6 ++
>  drivers/infiniband/sw/siw/siw_verbs.c           |   8 +-
>  drivers/infiniband/sw/siw/siw_verbs.h           |   3 +-
>  include/rdma/ib_umem.h                          |  14 ++-
>  include/rdma/ib_verbs.h                         |   4 +-
>  include/uapi/rdma/ib_user_ioctl_cmds.h          |  14 +++
>  37 files changed, 410 insertions(+), 34 deletions(-)
>  create mode 100644 drivers/infiniband/core/umem_dmabuf.c
>  create mode 100644 drivers/infiniband/core/umem_dmabuf.h
> 
> --
> 1.8.3.1

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