kho: remove finalize state and clients

Eliminate the `kho_finalize()` function and its associated state from the
KHO subsystem.  The transition to a radix tree for memory tracking makes
the explicit "finalize" state and its serialization step obsolete.

Remove the `kho_finalize()` and `kho_finalized()` APIs and their stub
implementations.  Update KHO client code and the debugfs interface to no
longer call or depend on the `kho_finalize()` mechanism.

Complete the move towards a stateless KHO, simplifying the overall design
by removing unnecessary state management.

Link: https://lkml.kernel.org/r/20260206021428.3386442-3-jasonmiu@google.com
Signed-off-by: Jason Miu <jasonmiu@google.com>
Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Changyuan Lyu <changyuanl@google.com>
Cc: David Matlack <dmatlack@google.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Pratyush Yadav <pratyush@kernel.org>
Cc: Ran Xiaokai <ran.xiaokai@zte.com.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 11 insertions, 42 deletions

diff --git a/Documentation/admin-guide/mm/kho.rst b/Documentation/admin-guide/mm/kho.rst
index 6dc18ed4b886..cb9a20f64920 100644
--- a/Documentation/admin-guide/mm/kho.rst
+++ b/Documentation/admin-guide/mm/kho.rst
@@ -28,20 +28,10 @@ per NUMA node scratch regions on boot.
 Perform a KHO kexec
 ===================
 
-First, before you perform a KHO kexec, you need to move the system into
-the :ref:`KHO finalization phase <kho-finalization-phase>` ::
-
-  $ echo 1 > /sys/kernel/debug/kho/out/finalize
-
-After this command, the KHO FDT is available in
-``/sys/kernel/debug/kho/out/fdt``. Other subsystems may also register
-their own preserved sub FDTs under
-``/sys/kernel/debug/kho/out/sub_fdts/``.
-
-Next, load the target payload and kexec into it. It is important that you
-use the ``-s`` parameter to use the in-kernel kexec file loader, as user
-space kexec tooling currently has no support for KHO with the user space
-based file loader ::
+To perform a KHO kexec, load the target payload and kexec into it. It
+is important that you use the ``-s`` parameter to use the in-kernel
+kexec file loader, as user space kexec tooling currently has no
+support for KHO with the user space based file loader ::
 
   # kexec -l /path/to/bzImage --initrd /path/to/initrd -s
   # kexec -e
@@ -52,40 +42,19 @@ For example, if you used ``reserve_mem`` command line parameter to create
 an early memory reservation, the new kernel will have that memory at the
 same physical address as the old kernel.
 
-Abort a KHO exec
-================
-
-You can move the system out of KHO finalization phase again by calling ::
-
-  $ echo 0 > /sys/kernel/debug/kho/out/active
-
-After this command, the KHO FDT is no longer available in
-``/sys/kernel/debug/kho/out/fdt``.
-
 debugfs Interfaces
 ==================
 
+These debugfs interfaces are available when the kernel is compiled with
+``CONFIG_KEXEC_HANDOVER_DEBUGFS`` enabled.
+
 Currently KHO creates the following debugfs interfaces. Notice that these
 interfaces may change in the future. They will be moved to sysfs once KHO is
 stabilized.
 
-``/sys/kernel/debug/kho/out/finalize``
-    Kexec HandOver (KHO) allows Linux to transition the state of
-    compatible drivers into the next kexec'ed kernel. To do so,
-    device drivers will instruct KHO to preserve memory regions,
-    which could contain serialized kernel state.
-    While the state is serialized, they are unable to perform
-    any modifications to state that was serialized, such as
-    handed over memory allocations.
-
-    When this file contains "1", the system is in the transition
-    state. When contains "0", it is not. To switch between the
-    two states, echo the respective number into this file.
-
 ``/sys/kernel/debug/kho/out/fdt``
-    When KHO state tree is finalized, the kernel exposes the
-    flattened device tree blob that carries its current KHO
-    state in this file. Kexec user space tooling can use this
+    The kernel exposes the flattened device tree blob that carries its
+    current KHO state in this file. Kexec user space tooling can use this
     as input file for the KHO payload image.
 
 ``/sys/kernel/debug/kho/out/scratch_len``
@@ -100,8 +69,8 @@ stabilized.
     it should place its payload images.
 
 ``/sys/kernel/debug/kho/out/sub_fdts/``
-    In the KHO finalization phase, KHO producers register their own
-    FDT blob under this directory.
+    KHO producers can register their own FDT or another binary blob under
+    this directory.
 
 ``/sys/kernel/debug/kho/in/fdt``
     When the kernel was booted with Kexec HandOver (KHO),