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

[Jiri Pirko <jiri@resnulli.us>]

Wed, May 13, 2026 at 07:51:24PM +0200, jgg@ziepe.ca wrote:
>On Wed, May 13, 2026 at 01:38:07PM +0200, Jiri Pirko wrote:
>> Tue, May 12, 2026 at 08:29:27PM CEST, jgg@ziepe.ca wrote:
>> >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..
>> 
>> Agreed. I would like to fix this in a follow-up patchset which would
>> look more or less like this (Claude generated):
>
>That plan seems right to me, lets just get it sorted before anything
>starts using the new uverbs flow.

Well, this is existing code with CQ legacy umem attrs. But sure, will
address this right after this patchset is merged.

>
>Also please look on the Sashiko report, I saw some interesting things

I don't see any url anywhere. Where to find it?