Re: [PATCH rdma-next v4 11/16] RDMA/mlx4: Use ib_umem_get_cq_buf() for user CQ buffer

[Jason Gunthorpe <jgg@ziepe.ca>]

On Thu, May 07, 2026 at 02:52:26PM +0200, Jiri Pirko wrote:
> +	cq->umem = ib_umem_get_cq_buf(&dev->ib_dev, udata, entries * cqe_size,
> +				      IB_ACCESS_LOCAL_WRITE);
> +	if (IS_ERR(cq->umem)) {
> +		err = PTR_ERR(cq->umem);
>  		goto err_cq;
>  	}
> +	if (cq->umem) {
> +		if (dev->dev->caps.flags2 & MLX4_DEV_CAP_FLAG2_SW_CQ_INIT) {
> +			err = -EOPNOTSUPP;
> +			goto err_umem;

Huh. this is getting pretty hacky.. The driver wants to memset the
user buf to 0xcc for some reason, and it already has a nice flow that
if that fails it tells the FW it fails and presumably is Ok.

The issue is it passes buf_addr around insead of having made an
ib_umem_memset() (which can reject dmabuf).

Looks easy enough, change sg_zero_buffer() to sg_fill_buffer() to
accept the 0xcc, ib_umem_memset() trivially calls it, remove the
buf_addr from the call chain, directly use the umem in the
mlx4_init_user_cqes(), remove the if above, use the
ib_umem_get_cq_buf_or_va() in the driver..

Leaving it like this just means the driver won't work with the new
uAPI with normal VA which is not desirable..

Jason