[PATCH v10 1/6] RDMA/umem: Support importing dma-buf as user memory region

[Xiong, Jianxin]

> -----Original Message-----
> From: Jason Gunthorpe <jgg at ziepe.ca>
> Sent: Thursday, November 12, 2020 4:31 PM
> To: Xiong, Jianxin <jianxin.xiong at intel.com>
> Cc: linux-rdma at vger.kernel.org; dri-devel at lists.freedesktop.org; Doug Ledford <dledford at redhat.com>; Leon Romanovsky
> <leon at kernel.org>; Sumit Semwal <sumit.semwal at linaro.org>; Christian Koenig <christian.koenig at amd.com>; Vetter, Daniel
> <daniel.vetter at intel.com>
> Subject: Re: [PATCH v10 1/6] RDMA/umem: Support importing dma-buf as user memory region
> 
> On Tue, Nov 10, 2020 at 01:41:12PM -0800, Jianxin Xiong wrote:
> > +struct ib_umem *ib_umem_dmabuf_get(struct ib_device *device,
> > +				   unsigned long offset, size_t size,
> > +				   int fd, int access,
> > +				   const struct dma_buf_attach_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(offset, (unsigned long)size, &end))
> > +		return ERR_PTR(-EINVAL);
> > +
> > +	if (unlikely(PAGE_ALIGN(end) < PAGE_SIZE))
> > +		return ERR_PTR(-EINVAL);
> 
> This is weird, what does it do?

This sequence is modeled after the following code from ib_umem_init_odp():

                if (check_add_overflow(umem_odp->umem.address,
                                       (unsigned long)umem_odp->umem.length,
                                       &end))
                        return -EOVERFLOW;
                end = ALIGN(end, page_size);
                if (unlikely(end < page_size))
                        return -EOVERFLOW;

The weird part seems to be checking if 'end' is 0, but that should have been covered
by check_add_overflow() already.

> 
> > +
> > +	if (unlikely(!ops || !ops->move_notify))
> > +		return ERR_PTR(-EINVAL);
> > +
> > +	umem_dmabuf = kzalloc(sizeof(*umem_dmabuf), GFP_KERNEL);
> > +	if (!umem_dmabuf)
> > +		return ERR_PTR(-ENOMEM);
> > +
> > +	umem = &umem_dmabuf->umem;
> > +	umem->ibdev = device;
> > +	umem->length = size;
> > +	umem->address = offset;
> > +	umem->writable = ib_access_writable(access);
> > +	umem->is_dmabuf = 1;
> > +
> > +	if (unlikely(!ib_umem_num_pages(umem))) {
> > +		ret = -EINVAL;
> > +		goto out_free_umem;
> > +	}
> > +
> > +	dmabuf = dma_buf_get(fd);
> > +	if (IS_ERR(dmabuf)) {
> > +		ret = PTR_ERR(dmabuf);
> > +		goto out_free_umem;
> > +	}
> > +
> > +	if (dmabuf->size < offset + size) {
> > +		ret = -EINVAL;
> > +		goto out_release_dmabuf;
> 
> offset + size == end, already computed, in fact move this above the kzalloc
> 
> Jason