Merge branch 'device-memory-tcp-tx'

Mina Almasry says:

====================
Device memory TCP TX

The TX path had been dropped from the Device Memory TCP patch series
post RFCv1 [1], to make that series slightly easier to review. This
series rebases the implementation of the TX path on top of the
net_iov/netmem framework agreed upon and merged. The motivation for
the feature is thoroughly described in the docs & cover letter of the
original proposal, so I don't repeat the lengthy descriptions here, but
they are available in [1].

Full outline on usage of the TX path is detailed in the documentation
included with this series.

Test example is available via the kselftest included in the series as well.

The series is relatively small, as the TX path for this feature largely
piggybacks on the existing MSG_ZEROCOPY implementation.

Patch Overview:
---------------

1. Documentation & tests to give high level overview of the feature
   being added.

1. Add netmem refcounting needed for the TX path.

2. Devmem TX netlink API.

3. Devmem TX net stack implementation.

4. Make dma-buf unbinding scheduled work to handle TX cases where it gets
   freed from contexts where we can't sleep.

5. Add devmem TX documentation.

6. Add scaffolding enabling driver support for netmem_tx. Add helpers, driver
feature flag, and docs to enable drivers to declare netmem_tx support.

7. Guard netmem_tx against being enabled against drivers that don't
   support it.

8. Add devmem_tx selftests. Add TX path to ncdevmem and add a test to
   devmem.py.

Testing:
--------

Testing is very similar to devmem TCP RX path. The ncdevmem test used
for the RX path is now augemented with client functionality to test TX
path.

* Test Setup:

Kernel: net-next with this RFC and memory provider API cherry-picked
locally.

Hardware: Google Cloud A3 VMs.

NIC: GVE with header split & RSS & flow steering support.

Performance results are not included with this version, unfortunately.
I'm having issues running the dma-buf exporter driver against the
upstream kernel on my test setup. The issues are specific to that
dma-buf exporter and do not affect this patch series. I plan to follow
up this series with perf fixes if the tests point to issues once they're
up and running.

Special thanks to Stan who took a stab at rebasing the TX implementation
on top of the netmem/net_iov framework merged. Parts of his proposal [2]
that are reused as-is are forked off into their own patches to give full
credit.

[1] https://lore.kernel.org/netdev/20240909054318.1809580-1-almasrymina@google.com/
[2] https://lore.kernel.org/netdev/20240913150913.1280238-2-sdf@fomichev.me/T/#m066dd407fbed108828e2c40ae50e3f4376ef57fd

Cc: sdf@fomichev.me
Cc: asml.silence@gmail.com
Cc: dw@davidwei.uk
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Victor Nogueira <victor@mojatatu.com>
Cc: Pedro Tammela <pctammela@mojatatu.com>
Cc: Samiullah Khawaja <skhawaja@google.com>
Cc: Kuniyuki Iwashima <kuniyu@amazon.com>

v14: https://lore.kernel.org/netdev/20250429032645.363766-1-almasrymina@google.com/
v13: https://lore.kernel.org/netdev/20250425204743.617260-1-almasrymina@google.com/
v12: https://lore.kernel.org/netdev/20250423031117.907681-1-almasrymina@google.com/
v11: https://lore.kernel.org/netdev/20250423031117.907681-1-almasrymina@google.com/
v10: https://lore.kernel.org/netdev/20250417231540.2780723-1-almasrymina@google.com/
v9: https://lore.kernel.org/netdev/20250415224756.152002-1-almasrymina@google.com/
v8: https://lore.kernel.org/netdev/20250308214045.1160445-1-almasrymina@google.com/
v7: https://lore.kernel.org/netdev/20250227041209.2031104-1-almasrymina@google.com/
v6: https://lore.kernel.org/netdev/20250222191517.743530-1-almasrymina@google.com/
v5: https://lore.kernel.org/netdev/20250220020914.895431-1-almasrymina@google.com/
v4: https://lore.kernel.org/netdev/20250203223916.1064540-1-almasrymina@google.com/
v3: https://patchwork.kernel.org/project/netdevbpf/list/?series=929401&state=*
RFC v2: https://patchwork.kernel.org/project/netdevbpf/list/?series=920056&state=*
====================

Link: https://patch.msgid.link/20250508004830.4100853-1-almasrymina@google.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

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