Test TCP MSS getting auto-adjusted. PSP adds an encapsulation overhead
of 40B per packet, when used in transport mode without any
virtualization cookie or other optional PSP header fields. The kernel
should adjust the MSS for a connection after PSP tx state is reached.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Daniel Zahka <daniel.zahka@gmail.com>
---
 tools/testing/selftests/drivers/net/psp.py | 52 ++++++++++++++++++++++
 1 file changed, 52 insertions(+)

diff --git a/tools/testing/selftests/drivers/net/psp.py b/tools/testing/selftests/drivers/net/psp.py
index e8c80ebfa2f6..37953838abf8 100755
--- a/tools/testing/selftests/drivers/net/psp.py
+++ b/tools/testing/selftests/drivers/net/psp.py
@@ -431,6 +431,45 @@ from lib.py import bkg, rand_port, wait_port_listen
         s.close()
 
 
+def _data_mss_adjust(cfg, ipver):
+    _init_psp_dev(cfg)
+
+    # First figure out what the MSS would be without any adjustments
+    s = _make_clr_conn(cfg, ipver)
+    s.send(b"0123456789abcdef" * 1024)
+    _check_data_rx(cfg, 16 * 1024)
+    mss = s.getsockopt(socket.IPPROTO_TCP, socket.TCP_MAXSEG)
+    _close_conn(cfg, s)
+
+    s = _make_psp_conn(cfg, 0, ipver)
+    try:
+        rx_assoc = cfg.pspnl.rx_assoc({"version": 0,
+                                     "dev-id": cfg.psp_dev_id,
+                                     "sock-fd": s.fileno()})
+        rx = rx_assoc['rx-key']
+        tx = _spi_xchg(s, rx)
+
+        rxmss = s.getsockopt(socket.IPPROTO_TCP, socket.TCP_MAXSEG)
+        ksft_eq(mss, rxmss)
+
+        cfg.pspnl.tx_assoc({"dev-id": cfg.psp_dev_id,
+                          "version": 0,
+                          "tx-key": tx,
+                          "sock-fd": s.fileno()})
+
+        txmss = s.getsockopt(socket.IPPROTO_TCP, socket.TCP_MAXSEG)
+        ksft_eq(mss, txmss + 40)
+
+        data_len = _send_careful(cfg, s, 100)
+        _check_data_rx(cfg, data_len)
+        _check_data_outq(s, 0)
+
+        txmss = s.getsockopt(socket.IPPROTO_TCP, socket.TCP_MAXSEG)
+        ksft_eq(mss, txmss + 40)
+    finally:
+        _close_psp_conn(cfg, s)
+
+
 def data_stale_key(cfg):
     """ Test send on a double-rotated key """
     _init_psp_dev(cfg)
@@ -470,6 +509,15 @@ from lib.py import bkg, rand_port, wait_port_listen
     return test_case
 
 
+def ipver_test_builder(name, test_func, ipver):
+    """Build test cases for each IP version"""
+    def test_case(cfg):
+        cfg.require_ipver(ipver)
+        test_case.__name__ = f"{name}_ip{ipver}"
+        test_func(cfg, ipver)
+    return test_case
+
+
 def main() -> None:
     """ Ksft boiler plate main """
 
@@ -497,6 +545,10 @@ from lib.py import bkg, rand_port, wait_port_listen
                     for version in range(0, 4)
                     for ipver in ("4", "6")
                 ]
+                cases += [
+                    ipver_test_builder("data_mss_adjust", _data_mss_adjust, ipver)
+                    for ipver in ("4", "6")
+                ]
 
                 ksft_run(cases=cases, globs=globals(),
                          case_pfx={"dev_", "data_", "assoc_"},
-- 
2.51.0