net/tls: add kernel-driven resync mechanism for TX

TLS offload drivers keep track of TCP seq numbers to make sure
the packets are fed into the HW in order.

When packets get dropped on the way through the stack, the driver
will get out of sync and have to use fallback encryption, but unless
TCP seq number is resynced it will never match the packets correctly
(or even worse - use incorrect record sequence number after TCP seq
wraps).

Existing drivers (mlx5) feed the entire record on every out-of-order
event, allowing FW/HW to always be in sync.

This patch adds an alternative, more akin to the RX resync.  When
driver sees a frame which is past its expected sequence number the
stream must have gotten out of order (if the sequence number is
smaller than expected its likely a retransmission which doesn't
require resync).  Driver will ask the stack to perform TX sync
before it submits the next full record, and fall back to software
crypto until stack has performed the sync.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 34 insertions, 1 deletions

diff --git a/Documentation/networking/tls-offload.rst b/Documentation/networking/tls-offload.rst
index d134d63307e78..048e5ca44824b 100644
--- a/Documentation/networking/tls-offload.rst
+++ b/Documentation/networking/tls-offload.rst
@@ -206,7 +206,11 @@ TX
 
 Segments transmitted from an offloaded socket can get out of sync
 in similar ways to the receive side-retransmissions - local drops
-are possible, though network reorders are not.
+are possible, though network reorders are not. There are currently
+two mechanisms for dealing with out of order segments.
+
+Crypto state rebuilding
+~~~~~~~~~~~~~~~~~~~~~~~
 
 Whenever an out of order segment is transmitted the driver provides
 the device with enough information to perform cryptographic operations.
@@ -225,6 +229,35 @@ was just a retransmission. The former is simpler, and does not require
 retransmission detection therefore it is the recommended method until
 such time it is proven inefficient.
 
+Next record sync
+~~~~~~~~~~~~~~~~
+
+Whenever an out of order segment is detected the driver requests
+that the ``ktls`` software fallback code encrypt it. If the segment's
+sequence number is lower than expected the driver assumes retransmission
+and doesn't change device state. If the segment is in the future, it
+may imply a local drop, the driver asks the stack to sync the device
+to the next record state and falls back to software.
+
+Resync request is indicated with:
+
+.. code-block:: c
+
+  void tls_offload_tx_resync_request(struct sock *sk, u32 got_seq, u32 exp_seq)
+
+Until resync is complete driver should not access its expected TCP
+sequence number (as it will be updated from a different context).
+Following helper should be used to test if resync is complete:
+
+.. code-block:: c
+
+  bool tls_offload_tx_resync_pending(struct sock *sk)
+
+Next time ``ktls`` pushes a record it will first send its TCP sequence number
+and TLS record number to the driver. Stack will also make sure that
+the new record will start on a segment boundary (like it does when
+the connection is initially added).
+
 RX
 --