Re: [PATCH v2] RDMA/rtrs: client: Fix clt_path::max_pages_per_mr calculation

[Michael Gur <michaelgur@nvidia.com>]

On 12/24/2025 11:50 AM, Honggang LI wrote:
> If device max_mr_size bits in the range [mr_page_shift+31:mr_page_shift]
> are zero, the `min3` function will set clt_path::max_pages_per_mr to
> zero.
>
> `alloc_path_reqs` will pass zero, which is invalid, as the third parameter
> to `ib_alloc_mr`.
>
> v1 -> v2:
> Correct the commit message and set max_pages_per_mr to U32_MAX
> as Michael Gur suggested.
> Fixes: 6a98d71daea1 ("RDMA/rtrs: client: main functionality")
> Signed-off-by: Honggang LI <honggangli@163.com>
> ---
>   drivers/infiniband/ulp/rtrs/rtrs-clt.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/drivers/infiniband/ulp/rtrs/rtrs-clt.c b/drivers/infiniband/ulp/rtrs/rtrs-clt.c
> index 71387811b281..e477d2c0ff35 100644
> --- a/drivers/infiniband/ulp/rtrs/rtrs-clt.c
> +++ b/drivers/infiniband/ulp/rtrs/rtrs-clt.c
> @@ -1464,6 +1464,8 @@ static void query_fast_reg_mode(struct rtrs_clt_path *clt_path)
>   	mr_page_shift      = max(12, ffs(ib_dev->attrs.page_size_cap) - 1);
>   	max_pages_per_mr   = ib_dev->attrs.max_mr_size;
>   	do_div(max_pages_per_mr, (1ull << mr_page_shift));
> +	if ((u32)max_pages_per_mr == 0)
> +		max_pages_per_mr = U32_MAX;
>   	clt_path->max_pages_per_mr =
>   		min3(clt_path->max_pages_per_mr, (u32)max_pages_per_mr,
>   		     ib_dev->attrs.max_fast_reg_page_list_len);

Checking after casting means you'll also assign U32_MAX when it's zero 
before the casting.
For that to happen in this case we'd need to have a device with 
max_mr_size smaller than it's lowest supported page_size.
I think it's safe to assume these are not valid device attributes, so 
we're safe here.

Reviewed-by: Michael Gur <michaelgur@nvidia.com>