Integrate the LUO with the KHO framework to enable passing LUO state
across a kexec reboot.

This patch implements the lifecycle integration with KHO:

1. Incoming State: During early boot (`early_initcall`), LUO checks if
   KHO is active. If so, it retrieves the "LUO" subtree, verifies the
   "luo-v1" compatibility string, and reads the `liveupdate-number` to
   track the update count.

2. Outgoing State: During late initialization (`late_initcall`), LUO
   allocates a new FDT for the next kernel, populates it with the basic
   header (compatible string and incremented update number), and
   registers it with KHO (`kho_add_subtree`).

3. Finalization: The `liveupdate_reboot()` notifier is updated to invoke
   `kho_finalize()`. This ensures that all memory segments marked for
   preservation are properly serialized before the kexec jump.

LUO now depends on `CONFIG_KEXEC_HANDOVER`.

Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
---
 include/linux/kho/abi/luo.h      |  54 +++++++++++
 kernel/liveupdate/luo_core.c     | 154 ++++++++++++++++++++++++++++++-
 kernel/liveupdate/luo_internal.h |  22 +++++
 3 files changed, 229 insertions(+), 1 deletion(-)
 create mode 100644 include/linux/kho/abi/luo.h
 create mode 100644 kernel/liveupdate/luo_internal.h

diff --git a/include/linux/kho/abi/luo.h b/include/linux/kho/abi/luo.h
new file mode 100644
index 000000000000..8523b3ff82d1
--- /dev/null
+++ b/include/linux/kho/abi/luo.h

@@ -0,0 +1,54 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * Copyright (c) 2025, Google LLC.
+ * Pasha Tatashin <pasha.tatashin@soleen.com>
+ */
+
+/**
+ * DOC: Live Update Orchestrator ABI
+ *
+ * This header defines the stable Application Binary Interface used by the
+ * Live Update Orchestrator to pass state from a pre-update kernel to a
+ * post-update kernel. The ABI is built upon the Kexec HandOver framework
+ * and uses a Flattened Device Tree to describe the preserved data.
+ *
+ * This interface is a contract. Any modification to the FDT structure, node
+ * properties, compatible strings, or the layout of the `__packed` serialization
+ * structures defined here constitutes a breaking change. Such changes require
+ * incrementing the version number in the relevant `_COMPATIBLE` string to
+ * prevent a new kernel from misinterpreting data from an old kernel.

+		/*
+		 * kho_finalize() may return libfdt errors, to aboid passing to
+		 * userspace unknown errors, change this to EAGAIN.
+		 */
+		err = -EAGAIN;
+	}
+
+	return err;
 }
 
 /**

diff --git a/kernel/liveupdate/luo_internal.h b/kernel/liveupdate/luo_internal.h
new file mode 100644
index 000000000000..8612687b2000
--- /dev/null
+++ b/kernel/liveupdate/luo_internal.h

@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * Copyright (c) 2025, Google LLC.
+ * Pasha Tatashin <pasha.tatashin@soleen.com>
+ */
+
+#ifndef _LINUX_LUO_INTERNAL_H
+#define _LINUX_LUO_INTERNAL_H
+
+#include <linux/liveupdate.h>
+
+/*
+ * Handles a deserialization failure: devices and memory is in unpredictable
+ * state.
+ *
+ * Continuing the boot process after a failure is dangerous because it could
+ * lead to leaks of private data.
+ */
+#define luo_restore_fail(__fmt, ...) panic(__fmt, ##__VA_ARGS__)