liveupdate: register luo_ser as KHO subtree

Entirely remove the LUO FDT wrapper since the FDT only carries the
compatible string and the pointer to the centralized struct luo_ser.
Instead, register the struct luo_ser via the KHO raw subtree
API, placing the compatibility string inside the structure itself.

Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Pratyush Yadav (Google) <pratyush@kernel.org>
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Link: https://patch.msgid.link/20260603154402.468928-5-pasha.tatashin@soleen.com
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

1 files changed, 21 insertions, 36 deletions

diff --git a/include/linux/kho/abi/luo.h b/include/linux/kho/abi/luo.h
index 1b2f865a771a..9a4fe491812b 100644
--- a/include/linux/kho/abi/luo.h
+++ b/include/linux/kho/abi/luo.h
@@ -10,11 +10,11 @@
  *
  * Live Update Orchestrator uses the stable Application Binary Interface
  * defined below 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.
+ * kernel. The ABI is built upon the Kexec HandOver framework and registers
+ * the central `struct luo_ser` via the KHO raw subtree API.
  *
- * This interface is a contract. Any modification to the FDT structure, node
- * properties, compatible strings, or the layout of the `__packed` serialization
+ * This interface is a contract. Any modification to the structure fields,
+ * 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.
@@ -23,31 +23,15 @@
  * however, backward/forward compatibility is only guaranteed for kernels
  * supporting the same ABI version.
  *
- * FDT Structure Overview:
+ * KHO Structure Overview:
  *   The entire LUO state is encapsulated within a single KHO entry named "LUO".
- *   This entry contains an FDT with the following layout:
- *
- *   .. code-block:: none
- *
- *     / {
- *         compatible = "luo-v2";
- *         luo-abi-header = <phys_addr_of_luo_ser>;
- *     };
- *
- * Main LUO Node (/):
- *
- *   - compatible: "luo-v2"
- *     Identifies the overall LUO ABI version.
- *   - luo-abi-header: u64
- *     The physical address of `struct luo_ser`.
+ *   This entry contains the `struct luo_ser` structure.
  *
  * Serialization Structures:
- *   The FDT properties point to memory regions containing arrays of simple,
- *   `__packed` structures. These structures contain the actual preserved state.
- *
  *   - struct luo_ser:
  *     The central ABI structure that contains the overall state of the LUO.
- *     It includes the liveupdate-number and pointers to sessions and FLBs.
+ *     It includes the compatibility string, the liveupdate-number, and pointers
+ *     to sessions and FLBs.
  *
  *   - struct luo_session_header_ser:
  *     Header for the session array. Contains the total page count of the
@@ -78,26 +62,27 @@
 #ifndef _LINUX_KHO_ABI_LUO_H
 #define _LINUX_KHO_ABI_LUO_H
 
+#include <linux/align.h>
 #include <uapi/linux/liveupdate.h>
 
 /*
- * The LUO FDT hooks all LUO state for sessions, fds, etc.
+ * The LUO state is registered under this KHO entry name.
  */
-#define LUO_FDT_SIZE		PAGE_SIZE
-#define LUO_FDT_KHO_ENTRY_NAME	"LUO"
-#define LUO_FDT_COMPATIBLE	"luo-v2"
-#define LUO_FDT_ABI_HEADER	"luo-abi-header"
+#define LUO_KHO_ENTRY_NAME	"LUO"
+#define LUO_ABI_COMPATIBLE	"luo-v3"
+#define LUO_ABI_COMPAT_LEN	ALIGN(sizeof(LUO_ABI_COMPATIBLE), 8)
 
 /**
  * struct luo_ser - Centralized LUO ABI header.
+ * @compatible:     Compatibility string identifying the LUO ABI version.
  * @liveupdate_num: A counter tracking the number of successful live updates.
  * @sessions_pa:    Physical address of the first session block header.
  * @flbs_pa:        Physical address of the FLB header.
  *
- * This structure is the root of all preserved LUO state. It is pointed to by
- * the "luo-abi-header" property in the LUO FDT.
+ * This structure is the root of all preserved LUO state.
  */
 struct luo_ser {
+	char compatible[LUO_ABI_COMPAT_LEN];
 	u64 liveupdate_num;
 	u64 sessions_pa;
 	u64 flbs_pa;
@@ -111,7 +96,7 @@ struct luo_ser {
  * @data:        Private data
  * @token:       User provided token for this file
  *
- * If this structure is modified, LUO_SESSION_COMPATIBLE must be updated.
+ * If this structure is modified, `LUO_ABI_COMPATIBLE` must be updated.
  */
 struct luo_file_ser {
 	char compatible[LIVEUPDATE_HNDL_COMPAT_LENGTH];
@@ -142,7 +127,7 @@ struct luo_file_set_ser {
  * physical memory preserved across the kexec. It provides the necessary
  * metadata to interpret the array of session entries that follow.
  *
- * If this structure is modified, `LUO_FDT_COMPATIBLE` must be updated.
+ * If this structure is modified, `LUO_ABI_COMPATIBLE` must be updated.
  */
 struct luo_session_header_ser {
 	u64 count;
@@ -159,7 +144,7 @@ struct luo_session_header_ser {
  * session) is created and passed to the new kernel, allowing it to reconstruct
  * the session context.
  *
- * If this structure is modified, `LUO_FDT_COMPATIBLE` must be updated.
+ * If this structure is modified, `LUO_ABI_COMPATIBLE` must be updated.
  */
 struct luo_session_ser {
 	char name[LIVEUPDATE_SESSION_NAME_LENGTH];
@@ -180,7 +165,7 @@ struct luo_session_ser {
  * This structure is located at the physical address specified by the
  * flbs_pa in luo_ser.
  *
- * If this structure is modified, `LUO_FDT_COMPATIBLE` must be updated.
+ * If this structure is modified, `LUO_ABI_COMPATIBLE` must be updated.
  */
 struct luo_flb_header_ser {
 	u64 pgcnt;
@@ -202,7 +187,7 @@ struct luo_flb_header_ser {
  * passed to the new kernel. Each entry allows the LUO core to restore one
  * global, shared object.
  *
- * If this structure is modified, `LUO_FDT_COMPATIBLE` must be updated.
+ * If this structure is modified, `LUO_ABI_COMPATIBLE` must be updated.
  */
 struct luo_flb_ser {
 	char name[LIVEUPDATE_FLB_COMPAT_LENGTH];