psp: Add support for dev-assoc/disassoc

From: Wei Wang <weibunny@fb.com>

The main purpose of this feature is to associate virtual devices like
veth or netkit with a real PSP device, so we could provide PSP
functionality to the application running with virtual devices.

A typical deployment that works with this feature is as follows:
     Host Namespace:
     psp_dev_local  ←──physically linked──→ psp_dev_peer
	  (PSP device)
	       │
	       │ BPF on psp_dev_local ingress: bpf_redirect_peer() to nk_guest
	       │
	  nk_host / veth_host
	       │
	       │ BPF on nk_host ingress: bpf_redirect_neigh() to psp_dev_local
	       │
      Guest Namespace (netns):
	       │
	  nk_guest / veth_guest
	  ★ PSP application run here

      Remote Namespace (_netns):
	  psp_dev_peer
	  ★ PSP server application runs here

Note:
The general requirement for this feature to work:
For PSP to work correctly, the egress device at validate_xmit_skb()
time must have psp_dev matching the association's psd. Any device
stacking or traffic redirection that changes the egress device will
cause either:
1. TX validation failure (SKB_DROP_REASON_PSP_OUTPUT) - fail-safe
2. RX policy failure after tx-assoc - packets without PSP extension
   are rejected by receiver expecting encrypted traffic

Here are a few examples that this feature would not work:
- Bonding with load balancing in round-robin, XOR, 802.3ad mode across
  multiple PSP devices, or mixed PSP and non-PSP devices
- Bonding with active-backup mode might work without PSP migration for
  failover case.
- ipvlan/macvlan in bridge mode would not work given packets are
  loopbacked locally without going through the PSP device.

Changes since v7:
- Refactor in patch 1 to have a common helper for
  psp_device_get_locked_admin() and psp_device_get_locked()
- Take psd->lock in psp_assoc_device_get_locked() before
  psp_dev_check_access() in patch 2
- Use cmpxchg() for assoc_dev->psp_dev assignment when doing dev-assoc
  in patch 2
- Check for err for register_netdevice_notifier() in patch 3
- Call psp_attach_netdev_notifier() in pre_doit handler for dev-assoc to
  avoid releasing of psd->lock in patch 3

Changes since v6:
- Remove the unused remote_addr, nk_guest_addr and import cmd in patch 5

Changes since v5:
- Remove module_exit() in patch 3

Changes since v4:
- Address compilation warning in patch 3
- Removed the call to psp_nl_has_listeners_any_ns() and check listeners
  when looping through netns in psp_nl_notify_dev() in patch 2. This
  makes sure we only send notification to netns that has listeners.

Changes since v3:
- Make nsid optional for dev-assoc/dev-disassoc operation, and use
  the ns user is in when it's not specified. Also added a test for this.
- Fix psp_nl_notify_dev() to compute the correct nsid relative to the
  listener's netns.
- Only register the new netdev event for psp dev cleanup upon the first
  successful dev-assoc operation.
- Change the following in selftest:
  - Add CONFIG_NETKIT to driver/net's config
  - Fall back to NetDrvEpEnv and run basic test cases if NetDrvContEnv
    does not load
  - Use ksft_variants instead of psp_ip_ver_test_builder

Changes since v2:
- Change the newly added parameter to psp_device_get_and_lock() to
  admin in patch 1. Introduce 2 device check functions:
  - psp_device_get_locked_admin() for dev-set and key-rotate
  - psp_device_get_locked() for all other operations
  Flip the logic for checking the dev_assoc_list accordingly in patch 2.
- Move psp_nl_notify_dev() before removing the dev from assoc_dev_list
  in psp_nl_dev_disassoc_doit() and correct the typo in commit msg in
  patch 2.
- Remove the threading and subprocess and some comment updates in patch 5. 

Changes since v1:
- Update the first 4 patches to reflect the latest changes in
  https://lore.kernel.org/netdev/20260302053315.1919859-1-d...
- Update patch 9 to add a param to NetDrvContEnv to control the loading
  of the tx forwarding bpf program

Wei Wang (5):
  psp: add admin/non-admin version of psp_device_get_locked
  psp: add new netlink cmd for dev-assoc and dev-disassoc
  psp: add a new netdev event for dev unregister
  selftests/net: Add bpf skb forwarding program
  selftest/net: psp: Add test for dev-assoc/disassoc

 Documentation/netlink/specs/psp.yaml          |  71 ++-
 include/net/psp/types.h                       |  15 +
 include/uapi/linux/psp.h                      |  13 +
 net/psp/psp-nl-gen.c                          |  36 +-
 net/psp/psp-nl-gen.h                          |   7 +
 net/psp/psp.h                                 |   3 +-
 net/psp/psp_main.c                            |  96 +++-
 net/psp/psp_nl.c                              | 352 ++++++++++++-
 tools/testing/selftests/drivers/net/config    |   1 +
 .../drivers/net/hw/nk_redirect.bpf.c          |  60 +++
 .../selftests/drivers/net/lib/py/env.py       |  54 +-
 tools/testing/selftests/drivers/net/psp.py    | 492 ++++++++++++++++--
 12 files changed, 1140 insertions(+), 60 deletions(-)
 create mode 100644 tools/testing/selftests/drivers/net/hw/nk_redirect.bpf.c

-- 
2.52.0