liveupdate: luo_session: add sessions support

Introduce concept of "Live Update Sessions" within the LUO framework.  LUO
sessions provide a mechanism to group and manage `struct file *` instances
(representing file descriptors) that need to be preserved across a
kexec-based live update.

Each session is identified by a unique name and acts as a container for
file objects whose state is critical to a userspace workload, such as a
virtual machine or a high-performance database, aiming to maintain their
functionality across a kernel transition.

This groundwork establishes the framework for preserving file-backed state
across kernel updates, with the actual file data preservation mechanisms
to be implemented in subsequent patches.

[dan.carpenter@linaro.org: fix use after free in luo_session_deserialize()]
  Link: https://lkml.kernel.org/r/c5dd637d7eed3a3be48c5e9fedb881596a3b1f5a.1764163896.git.dan.carpenter@linaro.org
Link: https://lkml.kernel.org/r/20251125165850.3389713-5-pasha.tatashin@soleen.com
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Tested-by: David Matlack <dmatlack@google.com>
Cc: Aleksander Lobakin <aleksander.lobakin@intel.com>
Cc: Alexander Graf <graf@amazon.com>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Andriy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: anish kumar <yesanishhere@gmail.com>
Cc: Anna Schumaker <anna.schumaker@oracle.com>
Cc: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Borislav Betkov <bp@alien8.de>
Cc: Chanwoo Choi <cw00.choi@samsung.com>
Cc: Chen Ridong <chenridong@huawei.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Daniel Wagner <wagi@kernel.org>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Jeffery <djeffery@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Guixin Liu <kanie@linux.alibaba.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Joanthan Cameron <Jonathan.Cameron@huawei.com>
Cc: Joel Granados <joel.granados@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Lennart Poettering <lennart@poettering.net>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: Leon Romanovsky <leonro@nvidia.com>
Cc: Lukas Wunner <lukas@wunner.de>
Cc: Marc Rutland <mark.rutland@arm.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Miguel Ojeda <ojeda@kernel.org>
Cc: Myugnjoo Ham <myungjoo.ham@samsung.com>
Cc: Parav Pandit <parav@nvidia.com>
Cc: Pratyush Yadav <ptyadav@amazon.de>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Saeed Mahameed <saeedm@nvidia.com>
Cc: Samiullah Khawaja <skhawaja@google.com>
Cc: Song Liu <song@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Stuart Hayes <stuart.w.hayes@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Cc: Thomas Weißschuh <linux@weissschuh.net>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: William Tu <witu@nvidia.com>
Cc: Yoann Congal <yoann.congal@smile.fr>
Cc: Zhu Yanjun <yanjun.zhu@linux.dev>
Cc: Zijun Hu <quic_zijuhu@quicinc.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: soleen

include/linux/kho/abi/luo.h

@@ -32,6 +32,11 @@
  *     / {
  *         compatible = "luo-v1";
  *         liveupdate-number = <...>;
+ *
+ *         luo-session {
+ *             compatible = "luo-session-v1";
+ *             luo-session-header = <phys_addr_of_session_header_ser>;
+ *         };
  *     };
  *
  * Main LUO Node (/):
@@ -40,11 +45,37 @@
  *     Identifies the overall LUO ABI version.
  *   - liveupdate-number: u64
  *     A counter tracking the number of successful live updates performed.
+ *
+ * Session Node (luo-session):
+ *   This node describes all preserved user-space sessions.
+ *
+ *   - compatible: "luo-session-v1"
+ *     Identifies the session ABI version.
+ *   - luo-session-header: u64
+ *     The physical address of a `struct luo_session_header_ser`. This structure
+ *     is the header for a contiguous block of memory containing an array of
+ *     `struct luo_session_ser`, one for each preserved session.
+ *
+ * Serialization Structures:
+ *   The FDT properties point to memory regions containing arrays of simple,
+ *   `__packed` structures. These structures contain the actual preserved state.
+ *
+ *   - 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
+ *     `struct luo_file_ser` for all files in that session.
  */
 
 #ifndef _LINUX_KHO_ABI_LUO_H
 #define _LINUX_KHO_ABI_LUO_H
 
+#include <uapi/linux/liveupdate.h>
+
 /*
  * The LUO FDT hooks all LUO state for sessions, fds, etc.
  * In the root it also carries "liveupdate-number" 64-bit property that
@@ -55,4 +86,44 @@
 #define LUO_FDT_COMPATIBLE	"luo-v1"
 #define LUO_FDT_LIVEUPDATE_NUM	"liveupdate-number"
 
+/*
+ * LUO FDT session node
+ * LUO_FDT_SESSION_HEADER:  is a u64 physical address of struct
+ *                          luo_session_header_ser
+ */
+#define LUO_FDT_SESSION_NODE_NAME	"luo-session"
+#define LUO_FDT_SESSION_COMPATIBLE	"luo-session-v1"
+#define LUO_FDT_SESSION_HEADER		"luo-session-header"
+
+/**
+ * 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_FDT_SESSION_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.
+ *
+ * This structure is used to package session-specific metadata for transfer
+ * between kernels via Kexec Handover. An array of these structures (one per
+ * session) is created and passed to the new kernel, allowing it to reconstruct
+ * the session context.
+ *
+ * If this structure is modified, `LUO_FDT_SESSION_COMPATIBLE` must be updated.
+ */
+struct luo_session_ser {
+	char name[LIVEUPDATE_SESSION_NAME_LENGTH];
+} __packed;
+
 #endif /* _LINUX_KHO_ABI_LUO_H */

include/uapi/linux/liveupdate.h

@@ -43,4 +43,7 @@
 /* The ioctl type, documented in ioctl-number.rst */
 #define LIVEUPDATE_IOCTL_TYPE		0xBA
 
+/* The maximum length of session name including null termination */
+#define LIVEUPDATE_SESSION_NAME_LENGTH 64
+
 #endif /* _UAPI_LIVEUPDATE_H */

kernel/liveupdate/Makefile

@@ -1,7 +1,8 @@
 # SPDX-License-Identifier: GPL-2.0
 
 luo-y :=								\
-		luo_core.o
+		luo_core.o						\
+		luo_session.o
 
 obj-$(CONFIG_KEXEC_HANDOVER)		+= kexec_handover.o
 obj-$(CONFIG_KEXEC_HANDOVER_DEBUG)	+= kexec_handover_debug.o

kernel/liveupdate/luo_core.c

@@ -118,6 +118,10 @@ static int __init luo_early_startup(void)
 	pr_info("Retrieved live update data, liveupdate number: %lld\n",
 		luo_global.liveupdate_num);
 
+	err = luo_session_setup_incoming(luo_global.fdt_in);
+	if (err)
+		return err;
+
 	return 0;
 }
 
@@ -154,6 +158,7 @@ static int __init luo_fdt_setup(void)
 	err |= fdt_begin_node(fdt_out, "");
 	err |= fdt_property_string(fdt_out, "compatible", LUO_FDT_COMPATIBLE);
 	err |= fdt_property(fdt_out, LUO_FDT_LIVEUPDATE_NUM, &ln, sizeof(ln));
+	err |= luo_session_setup_outgoing(fdt_out);
 	err |= fdt_end_node(fdt_out);
 	err |= fdt_finish(fdt_out);
 	if (err)
@@ -211,6 +216,10 @@ int liveupdate_reboot(void)
 	if (!liveupdate_enabled())
 		return 0;
 
+	err = luo_session_serialize();
+	if (err)
+		return err;
+
 	err = kho_finalize();
 	if (err) {
 		pr_err("kho_finalize failed %d\n", err);

kernel/liveupdate/luo_internal.h

@@ -19,4 +19,33 @@
  */
 #define luo_restore_fail(__fmt, ...) panic(__fmt, ##__VA_ARGS__)
 
+/**
+ * struct luo_session - Represents an active or incoming Live Update session.
+ * @name:       A unique name for this session, used for identification and
+ *              retrieval.
+ * @ser:        Pointer to the serialized data for this session.
+ * @list:       A list_head member used to link this session into a global list
+ *              of either outgoing (to be preserved) or incoming (restored from
+ *              previous kernel) sessions.
+ * @retrieved:  A boolean flag indicating whether this session has been
+ *              retrieved by a consumer in the new kernel.
+ * @mutex:      protects fields in the luo_session.
+ */
+struct luo_session {
+	char name[LIVEUPDATE_SESSION_NAME_LENGTH];
+	struct luo_session_ser *ser;
+	struct list_head list;
+	bool retrieved;
+	struct mutex mutex;
+};
+
+int luo_session_create(const char *name, struct file **filep);
+int luo_session_retrieve(const char *name, struct file **filep);
+int __init luo_session_setup_outgoing(void *fdt);
+int __init luo_session_setup_incoming(void *fdt);
+int luo_session_serialize(void);
+int luo_session_deserialize(void);
+bool luo_session_quiesce(void);
+void luo_session_resume(void);
+
 #endif /* _LINUX_LUO_INTERNAL_H */