selftests: drv-net-hw: Add a test for symmetric RSS hash

Add a selftest that verifies symmetric RSS hash is working as intended.
The test runs iterations of traffic, swapping the src/dst UDP ports, and
verifies that the same RX queue is receiving the traffic in both cases.

Reviewed-by: Nimrod Oren <noren@nvidia.com>
Signed-off-by: Gal Pressman <gal@nvidia.com>
Link: https://patch.msgid.link/20250224174416.499070-5-gal@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/drivers/net/hw/rss_input_xfrm.py

@@ -0,0 +1,87 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+
+import multiprocessing
+import socket
+from lib.py import ksft_run, ksft_exit, ksft_eq, ksft_ge, cmd, fd_read_timeout
+from lib.py import NetDrvEpEnv
+from lib.py import EthtoolFamily, NetdevFamily
+from lib.py import KsftSkipEx, KsftFailEx
+from lib.py import rand_port
+
+
+def traffic(cfg, local_port, remote_port, ipver):
+    af_inet = socket.AF_INET if ipver == "4" else socket.AF_INET6
+    sock = socket.socket(af_inet, socket.SOCK_DGRAM)
+    sock.bind(("", local_port))
+    sock.connect((cfg.remote_addr_v[ipver], remote_port))
+    tgt = f"{ipver}:[{cfg.addr_v[ipver]}]:{local_port},sourceport={remote_port}"
+    cmd("echo a | socat - UDP" + tgt, host=cfg.remote)
+    fd_read_timeout(sock.fileno(), 5)
+    return sock.getsockopt(socket.SOL_SOCKET, socket.SO_INCOMING_CPU)
+
+
+def test_rss_input_xfrm(cfg, ipver):
+    """
+    Test symmetric input_xfrm.
+    If symmetric RSS hash is configured, send traffic twice, swapping the
+    src/dst UDP ports, and verify that the same queue is receiving the traffic
+    in both cases (IPs are constant).
+    """
+
+    if multiprocessing.cpu_count() < 2:
+        raise KsftSkipEx("Need at least two CPUs to test symmetric RSS hash")
+
+    input_xfrm = cfg.ethnl.rss_get(
+        {'header': {'dev-name': cfg.ifname}}).get('input_xfrm')
+
+    # Check for symmetric xor/or-xor
+    if not input_xfrm or (input_xfrm != 1 and input_xfrm != 2):
+        raise KsftSkipEx("Symmetric RSS hash not requested")
+
+    cpus = set()
+    successful = 0
+    for _ in range(100):
+        try:
+            port1 = rand_port(socket.SOCK_DGRAM)
+            port2 = rand_port(socket.SOCK_DGRAM)
+            cpu1 = traffic(cfg, port1, port2, ipver)
+            cpu2 = traffic(cfg, port2, port1, ipver)
+            cpus.update([cpu1, cpu2])
+            ksft_eq(
+                cpu1, cpu2, comment=f"Received traffic on different cpus with ports ({port1 = }, {port2 = }) while symmetric hash is configured")
+
+            successful += 1
+            if successful == 10:
+                break
+        except:
+            continue
+    else:
+        raise KsftFailEx("Failed to run traffic")
+
+    ksft_ge(len(cpus), 2,
+            comment=f"Received traffic on less than two cpus {cpus = }")
+
+
+def test_rss_input_xfrm_ipv4(cfg):
+    cfg.require_ipver("4")
+    test_rss_input_xfrm(cfg, "4")
+
+
+def test_rss_input_xfrm_ipv6(cfg):
+    cfg.require_ipver("6")
+    test_rss_input_xfrm(cfg, "6")
+
+
+def main() -> None:
+    with NetDrvEpEnv(__file__, nsim_test=False) as cfg:
+        cfg.ethnl = EthtoolFamily()
+        cfg.netdevnl = NetdevFamily()
+
+        ksft_run([test_rss_input_xfrm_ipv4, test_rss_input_xfrm_ipv6],
+                 args=(cfg, ))
+    ksft_exit()
+
+
+if __name__ == "__main__":
+    main()