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Date:   Sun, 13 Dec 2020 16:39:29 +0200
From:   Tariq Toukan <>
To:     "David S. Miller" <>,
        Jakub Kicinski <>
Cc:, Saeed Mahameed <>,
        Moshe Shemesh <>,
        Boris Pismenny <>,
        Tariq Toukan <>,
        Tariq Toukan <>
Subject: [PATCH net V3] net: Disable NETIF_F_HW_TLS_TX when HW_CSUM is disabled

With NETIF_F_HW_TLS_TX packets are encrypted in HW. This cannot be
logically done when HW_CSUM offload is off.

Fixes: 2342a8512a1e ("net: Add TLS TX offload features")
Signed-off-by: Tariq Toukan <>
Reviewed-by: Boris Pismenny <>
 Documentation/networking/tls-offload.rst | 8 +++++++-
 net/core/dev.c                           | 5 +++++
 2 files changed, 12 insertions(+), 1 deletion(-)


Please queue to -stable >= v4.18.

- Describe expected behavior for already opened connections.

- Documented the change in tls-offload.rst.

diff --git a/Documentation/networking/tls-offload.rst b/Documentation/networking/tls-offload.rst
index 37773da2bee5..0f55c6d540f9 100644
--- a/Documentation/networking/tls-offload.rst
+++ b/Documentation/networking/tls-offload.rst
@@ -524,7 +524,13 @@ on TCP retransmissions to handle corner cases is not acceptable.
 TLS device features
-Drivers should ignore the changes to TLS the device feature flags.
+Drivers should ignore the changes to the TLS device feature flags.
 These flags will be acted upon accordingly by the core ``ktls`` code.
 TLS device feature flags only control adding of new TLS connection
 offloads, old connections will remain active after flags are cleared.
+TLS encryption cannot be offloaded to devices without checksum calculation
+offload. Hence, TLS TX device feature flag requires NETIF_F_HW_CSUM being set.
+Disabling the latter implies clearing the former. Disabling TX checksum offload
+should not affect old connections, and drivers should make sure checksum
+calculation does not break for them.
diff --git a/net/core/dev.c b/net/core/dev.c
index 38412e70f761..bd06c270ad57 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -9602,6 +9602,11 @@ static netdev_features_t netdev_fix_features(struct net_device *dev,
+	if ((features & NETIF_F_HW_TLS_TX) && !(features & NETIF_F_HW_CSUM)) {
+		netdev_dbg(dev, "Dropping TLS TX HW offload feature since no CSUM feature.\n");
+		features &= ~NETIF_F_HW_TLS_TX;
+	}
 	return features;

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