On Sun, Oct 04, 2020 at 12:12:28PM -0700, Jianxin Xiong wrote:
Dma-buf is a standard cross-driver buffer sharing mechanism that can be used to support peer-to-peer access from RDMA devices.
Device memory exported via dma-buf is associated with a file descriptor. This is passed to the user space as a property associated with the buffer allocation. When the buffer is registered as a memory region, the file descriptor is passed to the RDMA driver along with other parameters.
Implement the common code for importing dma-buf object and mapping dma-buf pages.
Signed-off-by: Jianxin Xiong jianxin.xiong@intel.com Reviewed-by: Sean Hefty sean.hefty@intel.com Acked-by: Michael J. Ruhl michael.j.ruhl@intel.com
drivers/infiniband/core/Makefile | 2 +- drivers/infiniband/core/umem.c | 4 + drivers/infiniband/core/umem_dmabuf.c | 291 ++++++++++++++++++++++++++++++++++ drivers/infiniband/core/umem_dmabuf.h | 14 ++ drivers/infiniband/core/umem_odp.c | 12 ++ include/rdma/ib_umem.h | 19 ++- 6 files changed, 340 insertions(+), 2 deletions(-) create mode 100644 drivers/infiniband/core/umem_dmabuf.c create mode 100644 drivers/infiniband/core/umem_dmabuf.h
I think this is using ODP too literally, dmabuf isn't going to need fine grained page faults, and I'm not sure this locking scheme is OK - ODP is horrifically complicated.
If this is the approach then I think we should make dmabuf its own stand alone API, reg_user_mr_dmabuf()
The implementation in mlx5 will be much more understandable, it would just do dma_buf_dynamic_attach() and program the XLT exactly the same as a normal umem.
The move_notify() simply zap's the XLT and triggers a work to reload it after the move. Locking is provided by the dma_resv_lock. Only a small disruption to the page fault handler is needed.
- dma_resv_lock(umem_dmabuf->attach->dmabuf->resv, NULL);
- sgt = dma_buf_map_attachment(umem_dmabuf->attach,
DMA_BIDIRECTIONAL);- dma_resv_unlock(umem_dmabuf->attach->dmabuf->resv);
This doesn't look right, this lock has to be held up until the HW is prorgammed
The use of atomic looks probably wrong as well.
- k = 0;
- total_pages = ib_umem_odp_num_pages(umem_odp);
- for_each_sg(umem->sg_head.sgl, sg, umem->sg_head.nents, j) {
addr = sg_dma_address(sg);pages = sg_dma_len(sg) >> page_shift;while (pages > 0 && k < total_pages) {umem_odp->dma_list[k++] = addr | access_mask;umem_odp->npages++;addr += page_size;pages--;
This isn't fragmenting the sg into a page list properly, won't work for unaligned things
And really we don't need the dma_list for this case, with a fixed whole mapping DMA SGL a normal umem sgl is OK and the normal umem XLT programming in mlx5 is fine.
Jason