netdev - [PATCH net-next v2 7/8] selftests: drv-net: psp: add test for auto-adjusting TCP MSS

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Message-ID: <20250925211647.3450332-8-daniel.zahka@gmail.com>
Date: Thu, 25 Sep 2025 14:16:43 -0700
From: Daniel Zahka <daniel.zahka@...il.com>
To: Jakub Kicinski <kuba@...nel.org>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Shuah Khan <shuah@...nel.org>
Cc: Willem de Bruijn <willemb@...gle.com>,
	Breno Leitao <leitao@...ian.org>,
	Petr Machata <petrm@...dia.com>,
	Yuyang Huang <yuyanghuang@...gle.com>,
	Xiao Liang <shaw.leon@...il.com>,
	Carolina Jubran <cjubran@...dia.com>,
	Donald Hunter <donald.hunter@...il.com>,
	netdev@...r.kernel.org,
	linux-kselftest@...r.kernel.org
Subject: [PATCH net-next v2 7/8] selftests: drv-net: psp: add test for auto-adjusting TCP MSS

From: Jakub Kicinski <kuba@...nel.org>

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@...nel.org>
Signed-off-by: Daniel Zahka <daniel.zahka@...il.com>
---
 tools/testing/selftests/drivers/net/psp.py | 50 ++++++++++++++++++++++
 1 file changed, 50 insertions(+)

diff --git a/tools/testing/selftests/drivers/net/psp.py b/tools/testing/selftests/drivers/net/psp.py
index f9647371b791..3eed986e587e 100755
--- a/tools/testing/selftests/drivers/net/psp.py
+++ b/tools/testing/selftests/drivers/net/psp.py
@@ -383,6 +383,43 @@ def data_send_disconnect(cfg):
         s.close()
 
 
+def _data_mss_adjust(cfg, ipver):
+    # 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 """
 
@@ -421,6 +458,15 @@ def psp_ip_ver_test_builder(name, test_func, psp_ver, ipver):
     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:
     with NetDrvEpEnv(__file__) as cfg:
         cfg.pspnl = PSPFamily()
@@ -459,6 +505,10 @@ def main() -> None:
                     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")
+                ]
 
                 if cfg.psp_dev_id is not None:
                     ksft_run(cases=cases, globs=globals(),
-- 
2.47.3