Have you ever searched RDMA or smb-direct work in ISSUE of cifsd-team github?

cifsd-team#542
cifsd-team#604
and more... in ISSUE of cifsd-team github.

If so, could you please give some guidance on hardware, distro, specific steps, settings etc. used?

You should add "server multi channel support = yes" parameter in [global] section of your ksmbd.conf
and build ksmbd.ko after turning CONFIG_SMB_SERVER_SMBDIRECT config on.
The smb-direct(RDMA) feature is that the server responds from the client request. So please refer to your client settings or guide.

If it still doesn't work, please let me know.

Thank you for the input.

Yes, I had a look at various posts but still could not get it to work. Another one I found interesting but also without success: https://forum.level1techs.com/t/how-can-i-help-with-the-new-truenas-100g-testing/179052/8

As to my ksmbd.conf, it already has/had "server multi channel support = yes".
My kernel was build with CONFIG_SMB_SERVER_SMBDIRECT enabled, at least according to /boot/config-6.11.0-9-generic.

On the windows client I tracked RDMA activity with Perfmon. It apparently tries to establish RDMA connections, but they fail.

The only time I see any smb_direct messages in dmesg is immediately after start of the service:
[ +7.774154] ksmbd: selected SMB3_11 dialect idx = 3
[ +0.000009] ksmbd: selected SMB3_11 dialect idx = 3
[ +0.000179] ksmbd: smb_direct: ib device added: name rocep33s0f0
[ +0.000002] ksmbd: smb_direct: ib device added: name rocep33s0f1
[ +0.000354] ksmbd: smb_direct: init RDMA listener. cm_id=0000000084cd3fdd

The only time I see any smb_direct messages in dmesg is immediately after start of the service:

Is there any error messages from ksmbd: smb_direct: ? This message("ksmbd: smb_direct: init RDMA listener. cm_id=0000000084cd3fdd") is the last one ?