> -----Original Message-----
> From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Sent: Friday, October 16, 2020 5:28 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 v5 1/5] RDMA/umem: Support importing dma-buf as user memory region
>
> On Thu, Oct 15, 2020 at 03:02:45PM -0700, Jianxin Xiong wrote:
> > +struct ib_umem *ib_umem_dmabuf_get(struct ib_device *device,
> > + unsigned long addr, size_t size,
> > + int dmabuf_fd, int access,
> > + const struct ib_umem_dmabuf_ops *ops) {
> > + struct dma_buf *dmabuf;
> > + struct ib_umem_dmabuf *umem_dmabuf;
> > + struct ib_umem *umem;
> > + unsigned long end;
> > + long ret;
> > +
> > + if (check_add_overflow(addr, (unsigned long)size, &end))
> > + return ERR_PTR(-EINVAL);
> > +
> > + if (unlikely(PAGE_ALIGN(end) < PAGE_SIZE))
> > + return ERR_PTR(-EINVAL);
> > +
> > + if (unlikely(!ops || !ops->invalidate || !ops->update))
> > + return ERR_PTR(-EINVAL);
> > +
> > + umem_dmabuf = kzalloc(sizeof(*umem_dmabuf), GFP_KERNEL);
> > + if (!umem_dmabuf)
> > + return ERR_PTR(-ENOMEM);
> > +
> > + umem_dmabuf->ops = ops;
> > + INIT_WORK(&umem_dmabuf->work, ib_umem_dmabuf_work);
> > +
> > + umem = &umem_dmabuf->umem;
> > + umem->ibdev = device;
> > + umem->length = size;
> > + umem->address = addr;
>
> addr here is offset within the dma buf, but this code does nothing with it.
>
The current code assumes 0 offset, and 'addr' is the nominal starting address of the
buffer. If this is to be changed to offset, then yes, some more handling is needed
as you mentioned below.
> dma_buf_map_attachment gives a complete SGL for the entire DMA buf, but offset/length select a subset.
>
> You need to edit the sgls to make them properly span the sub-range and follow the peculiar rules for how SGLs in ib_umem's have to be
> constructed.
>
> Who validates that the total dma length of the SGL is exactly equal to length? That is really important too.
>
> Also, dma_buf_map_attachment() does not do the correct dma mapping for RDMA, eg it does not use ib_dma_map(). This is not a problem
> for mlx5 but it is troublesome to put in the core code.
ib_dma_map() uses dma_map_single(), GPU drivers use dma_map_resource() for
dma_buf_map_attachment(). They belong to the same family, but take different
address type (kernel address vs MMIO physical address). Could you elaborate what
the problem could be for non-mlx5 HCAs?
>
> Jason
