Merge branch 'add-bpf_xdp_get_xfrm_state-kfunc'

Merge branch 'add-bpf_xdp_get_xfrm_state-kfunc'

Daniel Xu says:

====================
Add bpf_xdp_get_xfrm_state() kfunc

This patchset adds two kfunc helpers, bpf_xdp_get_xfrm_state() and
bpf_xdp_xfrm_state_release() that wrap xfrm_state_lookup() and
xfrm_state_put(). The intent is to support software RSS (via XDP) for
the ongoing/upcoming ipsec pcpu work [0]. Recent experiments performed
on (hopefully) reproducible AWS testbeds indicate that single tunnel
pcpu ipsec can reach line rate on 100G ENA nics.

Note this patchset only tests/shows generic xfrm_state access. The
"secret sauce" (if you can really even call it that) involves accessing
a soon-to-be-upstreamed pcpu_num field in xfrm_state. Early example is
available here [1].

[0]: https://datatracker.ietf.org/doc/draft-ietf-ipsecme-multi-sa-performance/03/
[1]: https://github.com/danobi/xdp-tools/blob/e89a1c617aba3b50d990f779357d6ce2863ecb27/xdp-bench/xdp_redirect_cpumap.bpf.c#L385-L406

Changes from v5:
* Improve kfunc doc comments
* Remove extraneous replay-window setting on selftest reverse path
* Squash two kfunc commits into one
* Rebase to bpf-next to pick up bitfield write patches
* Remove testing of opts.error in selftest prog

Changes from v4:
* Fixup commit message for selftest
* Set opts->error -ENOENT for !x
* Revert single file xfrm + bpf

Changes from v3:
* Place all xfrm bpf integrations in xfrm_bpf.c
* Avoid using nval as a temporary
* Rebase to bpf-next
* Remove extraneous __failure_unpriv annotation for verifier tests

Changes from v2:
* Fix/simplify BPF_CORE_WRITE_BITFIELD() algorithm
* Added verifier tests for bitfield writes
* Fix state leakage across test_tunnel subtests

Changes from v1:
* Move xfrm tunnel tests to test_progs
* Fix writing to opts->error when opts is invalid
* Use __bpf_kfunc_start_defs()
* Remove unused vxlanhdr definition
* Add and use BPF_CORE_WRITE_BITFIELD() macro
* Make series bisect clean

Changes from RFCv2:
* Rebased to ipsec-next
* Fix netns leak

Changes from RFCv1:
* Add Antony's commit tags
* Add KF_ACQUIRE and KF_RELEASE semantics
====================

Reviewed-by: Eyal Birger <eyal.birger@gmail.com>
Link: https://lore.kernel.org/r/cover.1702593901.git.dxu@dxuuu.xyz
Signed-off-by: Alexei Starovoitov <ast@kernel.org>