netdev - Rx issues with Linux Bridge and thunderbolt-net

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Date: Thu, 7 Dec 2023 12:57:08 -0700
From: Arjun Mehta <arjunmeht@...il.com>
To: netdev@...r.kernel.org
Subject: Rx issues with Linux Bridge and thunderbolt-net 

Hi there, I’d like to report what I believe to be a bug with either Linux Bridge (maybe and/or thunderbolt-net as well).

Problem: Rx on bridged Thunderbolt interface are blocked

Reported Behavior:
Tested on Proxmox host via iperf3, between B550 Vision D-P and MacBook Pro (2019 intel). On a direct interface, thunderbolt bridge Tx and Rx speeds are equal and full speed (in my case 9GB/s each). However, when a thunderbolt bridge is passed through via Linux Bridge to a VM or container (in my case a Proxmox LXC container or VM) the bridge achieves full Tx speeds, but Rx speeds are reporting limited to ~30kb/s

Expected:
The VM/CT should have the same general performance for Tx AND Rx as the host

Reproducing:
- Setup for the bridge was done by following this guide: https://gist.github.com/scyto/67fdc9a517faefa68f730f82d7fa3570
- Both devices on Thunderbolt interfaces have static IPs
- VM is given the same IP, but unique MAC address
- BIOS has Thunderbolt security mode set to “No security”

Further reading:
The problem is outlined more with screenshots and further details in this Reddit post: https://www.reddit.com/r/Proxmox/comments/17kq5st/slow_rx_speed_from_thunderbolt_3_port_to_vm_over/.

Please let me know if there is any further action I can do to help investigate or where else I can direct the bug/concern

Thanks!
Arjun