> -----Original Message-----
> From: Jason Gunthorpe <jgg@xxxxxxxx>
> Sent: Monday, November 09, 2020 12:53 PM
> To: Xiong, Jianxin <jianxin.xiong@xxxxxxxxx>
> Cc: linux-rdma@xxxxxxxxxxxxxxx; dri-devel@xxxxxxxxxxxxxxxxxxxxx; Doug Ledford <dledford@xxxxxxxxxx>; Leon Romanovsky
> <leon@xxxxxxxxxx>; Sumit Semwal <sumit.semwal@xxxxxxxxxx>; Christian Koenig <christian.koenig@xxxxxxx>; Vetter, Daniel
> <daniel.vetter@xxxxxxxxx>
> Subject: Re: [PATCH v9 4/5] RDMA/mlx5: Support dma-buf based userspace memory region
>
> On Mon, Nov 09, 2020 at 11:23:00AM -0800, Jianxin Xiong wrote:
> > @@ -1291,8 +1303,11 @@ static struct mlx5_ib_mr *reg_create(struct ib_mr *ibmr, struct ib_pd *pd,
> > int err;
> > bool pg_cap = !!(MLX5_CAP_GEN(dev->mdev, pg));
> >
> > - page_size =
> > - mlx5_umem_find_best_pgsz(umem, mkc, log_page_size, 0, iova);
> > + if (umem->is_dmabuf)
> > + page_size = ib_umem_find_best_pgsz(umem, PAGE_SIZE, iova);
> > + else
> > + page_size = mlx5_umem_find_best_pgsz(umem, mkc, log_page_size,
> > + 0, iova);
>
> Any place touching the sgl has to also hold the resv lock, and sgl might be NULL since an invalidation could come in at any time, eg before
> we get here.
>
> You can avoid those problems by ingoring the SGL and hard wiring PAGE_SIZE here
>
> > +static int pagefault_dmabuf_mr(struct mlx5_ib_mr *mr, size_t bcnt,
> > + u32 *bytes_mapped, u32 flags) {
> > + struct ib_umem_dmabuf *umem_dmabuf = to_ib_umem_dmabuf(mr->umem);
> > + u32 xlt_flags = 0;
> > + int err;
> > +
> > + if (flags & MLX5_PF_FLAGS_ENABLE)
> > + xlt_flags |= MLX5_IB_UPD_XLT_ENABLE;
> > +
> > + dma_resv_lock(umem_dmabuf->attach->dmabuf->resv, NULL);
> > + err = ib_umem_dmabuf_map_pages(umem_dmabuf);
> > + if (!err)
> > + err = mlx5_ib_update_mr_pas(mr, xlt_flags);
>
> This still has to call mlx5_umem_find_best_pgsz() each time the sgl changes to ensure it is still Ok. Just checking that
>
> mlx5_umem_find_best_pgsz() > PAGE_SIZE
>
> and then throwing away the value is OK
ib_umem_find_best_pgsz() is already called inside ib_umem_dmabuf_map_pages(). Do we
still need to call mlx5_umem_find_best_pgsz() here?
>
> Jason
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