liveupdate: Remove limit on the number of sessions

Currently, the number of LUO sessions is limited by a fixed number of
pre-allocated pages for serialization (16 pages, allowing for ~819
sessions).

This limitation is problematic if LUO is used to support things such as
systemd file descriptor store, and would be used not just as VM memory
but to save other states on the machine.

Remove this limit by transitioning to a linked-block approach for
session metadata serialization. Instead of a single contiguous block,
session metadata is now stored in a chain of 16-page blocks. Each block
starts with a header containing the physical address of the next block
and the number of session entries in the current block.

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/20260603154402.468928-10-pasha.tatashin@soleen.com
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

1 files changed, 2 insertions, 21 deletions

diff --git a/include/linux/kho/abi/luo.h b/include/linux/kho/abi/luo.h
index 9a4fe491812b..03d940d0f9bb 100644
--- a/include/linux/kho/abi/luo.h
+++ b/include/linux/kho/abi/luo.h
@@ -33,11 +33,6 @@
  *     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
- *     preserved memory block and the number of `struct luo_session_ser`
- *     entries that follow.
- *
  *   - struct luo_session_ser:
  *     Metadata for a single session, including its name and a physical pointer
  *     to another preserved memory block containing an array of
@@ -63,13 +58,14 @@
 #define _LINUX_KHO_ABI_LUO_H
 
 #include <linux/align.h>
+#include <linux/kho/abi/block.h>
 #include <uapi/linux/liveupdate.h>
 
 /*
  * The LUO state is registered under this KHO entry name.
  */
 #define LUO_KHO_ENTRY_NAME	"LUO"
-#define LUO_ABI_COMPATIBLE	"luo-v3"
+#define LUO_ABI_COMPATIBLE	"luo-v4"
 #define LUO_ABI_COMPAT_LEN	ALIGN(sizeof(LUO_ABI_COMPATIBLE), 8)
 
 /**
@@ -119,21 +115,6 @@ struct luo_file_set_ser {
 } __packed;
 
 /**
- * struct luo_session_header_ser - Header for the serialized session data block.
- * @count: The number of `struct luo_session_ser` entries that immediately
- *         follow this header in the memory block.
- *
- * This structure is located at the beginning of a contiguous block of
- * 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_ABI_COMPATIBLE` must be updated.
- */
-struct luo_session_header_ser {
-	u64 count;
-} __packed;
-
-/**
  * struct luo_session_ser - Represents the serialized metadata for a LUO session.
  * @name:         The unique name of the session, provided by the userspace at
  *                the time of session creation.