[PATCH 13/14] docs: xfrm: include mark in XFRM_MSG_MIGRATE_STATE EEXIST tuple

[Steffen Klassert <steffen.klassert@secunet.com>]

From: Antony Antony <antony.antony@secunet.com>

Document mark as part of the EEXIST tuple and update the SA lookup
description to match.

Fixes: c13c0cc6f52e ("xfrm: add documentation for XFRM_MSG_MIGRATE_STATE")
Signed-off-by: Antony Antony <antony.antony@secunet.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
---
 .../networking/xfrm/xfrm_migrate_state.rst    | 25 +++++++++++++------
 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/Documentation/networking/xfrm/xfrm_migrate_state.rst b/Documentation/networking/xfrm/xfrm_migrate_state.rst
index 9d53cb22b007..ca2c9e5aaf33 100644
--- a/Documentation/networking/xfrm/xfrm_migrate_state.rst
+++ b/Documentation/networking/xfrm/xfrm_migrate_state.rst
@@ -27,15 +27,20 @@ SA Identification
 =================
 
 The struct is defined in ``include/uapi/linux/xfrm.h``. The SA is looked
-up using ``xfrm_state_lookup()`` with ``id.spi``,
-``id.daddr``, ``id.proto``, ``id.family``, and
-``old_mark.v & old_mark.m`` as the mark key::
+up using ``xfrm_state_lookup_exact()`` with ``id.spi``, ``id.daddr``,
+``id.proto``, ``id.family``, and an exact match against ``old_mark.v``
+and ``old_mark.m``. Unlike the data path, which uses a masked
+comparison, this requires the SA's mark and mask to equal ``old_mark``
+exactly, so a broad-mask SA is never matched when a more specific one
+was intended. If no such SA exists, ``-ESRCH`` is returned.
+
+The layout is::
 
     struct xfrm_user_migrate_state {
         struct xfrm_usersa_id  id;       /* spi, daddr, proto, family */
         xfrm_address_t         new_daddr;
         xfrm_address_t         new_saddr;
-        struct xfrm_mark       old_mark; /* SA lookup: key = v & m */
+        struct xfrm_mark       old_mark; /* SA lookup key (exact v/m match) */
         struct xfrm_selector   new_sel;  /* new selector (see Flags) */
         __u32                  new_reqid;
         __u32                  flags;    /* XFRM_MIGRATE_STATE_* */
@@ -72,8 +77,8 @@ inherits the value from the existing SA (omit-to-inherit).
      - Description
    * - ``XFRMA_MARK``
      - Mark on the migrated SA (``struct xfrm_mark``). Absent inherits
-       ``old_mark``. To use no mark on the new SA, send ``XFRMA_MARK``
-       with ``{0, 0}``.
+       the mark of the existing SA. To use no mark on the new SA, send
+       ``XFRMA_MARK`` with ``{0, 0}``.
    * - ``XFRMA_ENCAP``
      - UDP encapsulation template; only ``UDP_ENCAP_ESPINUDP`` is supported.
        Set ``encap_type=0`` to remove encap.
@@ -259,8 +264,12 @@ Attributes in the notification
 Error Handling
 ==============
 
-If the target SA tuple (new daddr, SPI, proto, new family) is already
-occupied, the operation returns ``-EEXIST`` before the migration begins.
+If the target SA tuple (new daddr, SPI, proto, new family, mark) is
+already occupied, the operation returns ``-EEXIST`` before the migration
+begins. "Occupied" includes wildcard shadowing: an existing SA with a
+broader mask (e.g. mark 0/0) claims every mark value, so it blocks
+migrating to any more specific mark at the same tuple, not just an
+exact mark/mask duplicate.
 The old SA remains intact and the operation is safe to retry after
 resolving the conflict.
 
-- 
2.53.0