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. Signed-off-by: Pasha Tatashin --- include/linux/liveupdate/abi/luo.h | 83 +++++- include/uapi/linux/liveupdate.h | 3 + kernel/liveupdate/Makefile | 3 +- kernel/liveupdate/luo_core.c | 10 + kernel/liveupdate/luo_internal.h | 52 ++++ kernel/liveupdate/luo_session.c | 421 +++++++++++++++++++++++++++++ 6 files changed, 570 insertions(+), 2 deletions(-) create mode 100644 kernel/liveupdate/luo_internal.h create mode 100644 kernel/liveupdate/luo_session.c diff --git a/include/linux/liveupdate/abi/luo.h b/include/linux/liveupdate/abi/luo.h index 9483a294287f..03a177ae232e 100644 --- a/include/linux/liveupdate/abi/luo.h +++ b/include/linux/liveupdate/abi/luo.h @@ -28,6 +28,11 @@ * / { * compatible = "luo-v1"; * liveupdate-number = <...>; + * + * luo-session { + * compatible = "luo-session-v1"; + * luo-session-header = ; + * }; * }; * * Main LUO Node (/): @@ -36,14 +41,40 @@ * 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_LIVEUPDATE_ABI_LUO_H #define _LINUX_LIVEUPDATE_ABI_LUO_H +#include + /* * The LUO FDT hooks all LUO state for sessions, fds, etc. - * In the root it allso carries "liveupdate-number" 64-bit property that + * In the root it also carries "liveupdate-number" 64-bit property that * corresponds to the number of live-updates performed on this machine. */ #define LUO_FDT_SIZE PAGE_SIZE @@ -51,4 +82,54 @@ #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. + * @pgcnt: The total size, in pages, of the entire preserved memory block + * that this header describes. + * @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. + */ +struct luo_session_header_ser { + u64 pgcnt; + u64 count; +} __packed; + +/** + * struct luo_session_ser - Represents the serialized metadata for a LUO session. + * @name: The unique name of the session, copied from the `luo_session` + * structure. + * @files: The physical address of a contiguous memory block that holds + * the serialized state of files. + * @pgcnt: The number of pages occupied by the `files` memory block. + * @count: The total number of files that were part of this session during + * serialization. Used for iteration and validation during + * restoration. + * + * 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_SESSION_COMPATIBLE must be updated. + */ +struct luo_session_ser { + char name[LIVEUPDATE_SESSION_NAME_LENGTH]; + u64 files; + u64 pgcnt; + u64 count; +} __packed; + #endif /* _LINUX_LIVEUPDATE_ABI_LUO_H */ diff --git a/include/uapi/linux/liveupdate.h b/include/uapi/linux/liveupdate.h index df34c1642c4d..d2ef2f7e0dbd 100644 --- a/include/uapi/linux/liveupdate.h +++ b/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 56 + #endif /* _UAPI_LIVEUPDATE_H */ diff --git a/kernel/liveupdate/Makefile b/kernel/liveupdate/Makefile index 413722002b7a..83285e7ad726 100644 --- a/kernel/liveupdate/Makefile +++ b/kernel/liveupdate/Makefile @@ -2,7 +2,8 @@ luo-y := \ luo_core.o \ - luo_ioctl.o + luo_ioctl.o \ + luo_session.o obj-$(CONFIG_KEXEC_HANDOVER) += kexec_handover.o obj-$(CONFIG_KEXEC_HANDOVER_DEBUG) += kexec_handover_debug.o diff --git a/kernel/liveupdate/luo_core.c b/kernel/liveupdate/luo_core.c index 4a213b262b9f..653cdca5e25d 100644 --- a/kernel/liveupdate/luo_core.c +++ b/kernel/liveupdate/luo_core.c @@ -54,6 +54,7 @@ #include #include "kexec_handover_internal.h" +#include "luo_internal.h" static struct { bool enabled; @@ -117,6 +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; } @@ -153,6 +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) @@ -210,6 +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); diff --git a/kernel/liveupdate/luo_internal.h b/kernel/liveupdate/luo_internal.h new file mode 100644 index 000000000000..245373edfa6f --- /dev/null +++ b/kernel/liveupdate/luo_internal.h @@ -0,0 +1,52 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +/* + * Copyright (c) 2025, Google LLC. + * Pasha Tatashin + */ + +#ifndef _LINUX_LUO_INTERNAL_H +#define _LINUX_LUO_INTERNAL_H + +#include + +/** + * struct luo_session - Represents an active or incoming Live Update session. + * @name: A unique name for this session, used for identification and + * retrieval. + * @files_list: An ordered list of files associated with this session, it is + * ordered by preservation time. + * @ser: Pointer to the serialized data for this session. + * @count: A counter tracking the number of files currently stored in the + * @files_list 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: Session lock, protects files_list, and count. + * @files: The physically contiguous memory block that holds the serialized + * state of files. + * @pgcnt: The number of pages @files occupy. + */ +struct luo_session { + char name[LIVEUPDATE_SESSION_NAME_LENGTH]; + struct list_head files_list; + struct luo_session_ser *ser; + long count; + struct list_head list; + bool retrieved; + struct mutex mutex; + struct luo_file_ser *files; + u64 pgcnt; +}; + +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_is_deserialized(void); + +#endif /* _LINUX_LUO_INTERNAL_H */ diff --git a/kernel/liveupdate/luo_session.c b/kernel/liveupdate/luo_session.c new file mode 100644 index 000000000000..cb74bfaba479 --- /dev/null +++ b/kernel/liveupdate/luo_session.c @@ -0,0 +1,421 @@ +// SPDX-License-Identifier: GPL-2.0 + +/* + * Copyright (c) 2025, Google LLC. + * Pasha Tatashin + */ + +/** + * DOC: LUO Sessions + * + * LUO Sessions provide the core mechanism for grouping and managing `struct + * file *` instances that need to be preserved across a kexec-based live + * update. Each session acts as a named container for a set of file objects, + * allowing a userspace agent to manage the lifecycle of resources critical to a + * workload. + * + * Core Concepts: + * + * - Named Containers: Sessions are identified by a unique, user-provided name, + * which is used for both creation in the current kernel and retrieval in the + * next kernel. + * + * - Userspace Interface: Session management is driven from userspace via + * ioctls on /dev/liveupdate. + * + * - Serialization: Session metadata is preserved using the KHO framework. When + * a live update is triggered via kexec, an array of `struct luo_session_ser` + * is populated and placed in a preserved memory region. An FDT node is also + * created, containing the count of sessions and the physical address of this + * array. + * + * Session Lifecycle: + * + * 1. Creation: A userspace agent calls `luo_session_create()` to create a + * new, empty session and receives a file descriptor for it. + * + * 2. Serialization: When the `reboot(LINUX_REBOOT_CMD_KEXEC)` syscall is + * made, `luo_session_serialize()` is called. It iterates through all + * active sessions and writes their metadata into a memory area preserved + * by KHO. + * + * 3. Deserialization (in new kernel): After kexec, `luo_session_deserialize()` + * runs, reading the serialized data and creating a list of `struct + * luo_session` objects representing the preserved sessions. + * + * 4. Retrieval: A userspace agent in the new kernel can then call + * `luo_session_retrieve()` with a session name to get a new file + * descriptor and access the preserved state. + */ + +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include "luo_internal.h" + +/* 16 4K pages, give space for 819 sessions */ +#define LUO_SESSION_PGCNT 16ul +#define LUO_SESSION_MAX (((LUO_SESSION_PGCNT << PAGE_SHIFT) - \ + sizeof(struct luo_session_header_ser)) / \ + sizeof(struct luo_session_ser)) + +/** + * struct luo_session_header - Header struct for managing LUO sessions. + * @count: The number of sessions currently tracked in the @list. + * @list: The head of the linked list of `struct luo_session` instances. + * @rwsem: A read-write semaphore providing synchronized access to the + * session list and other fields in this structure. + * @header_ser: The header data of serialization array. + * @ser: The serialized session data (an array of + * `struct luo_session_ser`). + * @active: Set to true when first initialized. If previous kernel did not + * send session data, active stays false for incoming. + */ +struct luo_session_header { + long count; + struct list_head list; + struct rw_semaphore rwsem; + struct luo_session_header_ser *header_ser; + struct luo_session_ser *ser; + bool active; +}; + +/** + * struct luo_session_global - Global container for managing LUO sessions. + * @incoming: The sessions passed from the previous kernel. + * @outgoing: The sessions that are going to be passed to the next kernel. + * @deserialized: The sessions have been deserialized once /dev/liveupdate + * has been opened. + */ +struct luo_session_global { + struct luo_session_header incoming; + struct luo_session_header outgoing; + bool deserialized; +}; + +static struct luo_session_global luo_session_global; + +static struct luo_session *luo_session_alloc(const char *name) +{ + struct luo_session *session = kzalloc(sizeof(*session), GFP_KERNEL); + + if (!session) + return ERR_PTR(-ENOMEM); + + strscpy(session->name, name, sizeof(session->name)); + INIT_LIST_HEAD(&session->files_list); + INIT_LIST_HEAD(&session->list); + mutex_init(&session->mutex); + session->count = 0; + + return session; +} + +static void luo_session_free(struct luo_session *session) +{ + WARN_ON(session->count); + WARN_ON(!list_empty(&session->files_list)); + mutex_destroy(&session->mutex); + kfree(session); +} + +static int luo_session_insert(struct luo_session_header *sh, + struct luo_session *session) +{ + struct luo_session *it; + + guard(rwsem_write)(&sh->rwsem); + + /* + * For outgoing we should make sure there is room in serialization array + * for new session. + */ + if (sh == &luo_session_global.outgoing) { + if (sh->count == LUO_SESSION_MAX) + return -ENOMEM; + } + + /* + * For small number of sessions this loop won't hurt performance + * but if we ever start using a lot of sessions, this might + * become a bottle neck during deserialization time, as it would + * cause O(n*n) complexity. + */ + list_for_each_entry(it, &sh->list, list) { + if (!strncmp(it->name, session->name, sizeof(it->name))) + return -EEXIST; + } + list_add_tail(&session->list, &sh->list); + sh->count++; + + return 0; +} + +static void luo_session_remove(struct luo_session_header *sh, + struct luo_session *session) +{ + guard(rwsem_write)(&sh->rwsem); + list_del(&session->list); + sh->count--; +} + +static int luo_session_release(struct inode *inodep, struct file *filep) +{ + struct luo_session *session = filep->private_data; + struct luo_session_header *sh; + + /* If retrieved is set, it means this session is from incoming list */ + if (session->retrieved) + sh = &luo_session_global.incoming; + else + sh = &luo_session_global.outgoing; + + luo_session_remove(sh, session); + luo_session_free(session); + + return 0; +} + +static const struct file_operations luo_session_fops = { + .owner = THIS_MODULE, + .release = luo_session_release, +}; + +/* Create a "struct file" for session */ +static int luo_session_getfile(struct luo_session *session, struct file **filep) +{ + char name_buf[128]; + struct file *file; + + guard(mutex)(&session->mutex); + snprintf(name_buf, sizeof(name_buf), "[luo_session] %s", session->name); + file = anon_inode_getfile(name_buf, &luo_session_fops, session, O_RDWR); + if (IS_ERR(file)) + return PTR_ERR(file); + + *filep = file; + + return 0; +} + +int luo_session_create(const char *name, struct file **filep) +{ + struct luo_session *session; + int err; + + session = luo_session_alloc(name); + if (IS_ERR(session)) + return PTR_ERR(session); + + err = luo_session_insert(&luo_session_global.outgoing, session); + if (err) + goto err_free; + + err = luo_session_getfile(session, filep); + if (err) + goto err_remove; + + return 0; + +err_remove: + luo_session_remove(&luo_session_global.outgoing, session); +err_free: + luo_session_free(session); + + return err; +} + +int luo_session_retrieve(const char *name, struct file **filep) +{ + struct luo_session_header *sh = &luo_session_global.incoming; + struct luo_session *session = NULL; + struct luo_session *it; + int err; + + scoped_guard(rwsem_read, &sh->rwsem) { + list_for_each_entry(it, &sh->list, list) { + if (!strncmp(it->name, name, sizeof(it->name))) { + session = it; + break; + } + } + } + + if (!session) + return -ENOENT; + + scoped_guard(mutex, &session->mutex) { + if (session->retrieved) + return -EINVAL; + } + + err = luo_session_getfile(session, filep); + if (!err) { + scoped_guard(mutex, &session->mutex) + session->retrieved = true; + } + + return err; +} + +int __init luo_session_setup_outgoing(void *fdt_out) +{ + struct luo_session_header_ser *header_ser; + u64 header_ser_pa; + int err; + + header_ser = kho_alloc_preserve(LUO_SESSION_PGCNT << PAGE_SHIFT); + if (IS_ERR(header_ser)) + return PTR_ERR(header_ser); + header_ser_pa = virt_to_phys(header_ser); + + err = fdt_begin_node(fdt_out, LUO_FDT_SESSION_NODE_NAME); + err |= fdt_property_string(fdt_out, "compatible", + LUO_FDT_SESSION_COMPATIBLE); + err |= fdt_property(fdt_out, LUO_FDT_SESSION_HEADER, &header_ser_pa, + sizeof(header_ser_pa)); + err |= fdt_end_node(fdt_out); + + if (err) + goto err_unpreserve; + + header_ser->pgcnt = LUO_SESSION_PGCNT; + INIT_LIST_HEAD(&luo_session_global.outgoing.list); + init_rwsem(&luo_session_global.outgoing.rwsem); + luo_session_global.outgoing.header_ser = header_ser; + luo_session_global.outgoing.ser = (void *)(header_ser + 1); + luo_session_global.outgoing.active = true; + + return 0; + +err_unpreserve: + kho_unpreserve_free(header_ser); + return err; +} + +int __init luo_session_setup_incoming(void *fdt_in) +{ + struct luo_session_header_ser *header_ser; + int err, header_size, offset; + u64 header_ser_pa; + const void *ptr; + + offset = fdt_subnode_offset(fdt_in, 0, LUO_FDT_SESSION_NODE_NAME); + if (offset < 0) { + pr_err("Unable to get session node: [%s]\n", + LUO_FDT_SESSION_NODE_NAME); + return -EINVAL; + } + + err = fdt_node_check_compatible(fdt_in, offset, + LUO_FDT_SESSION_COMPATIBLE); + if (err) { + pr_err("Session node incompatible [%s]\n", + LUO_FDT_SESSION_COMPATIBLE); + return -EINVAL; + } + + header_size = 0; + ptr = fdt_getprop(fdt_in, offset, LUO_FDT_SESSION_HEADER, &header_size); + if (!ptr || header_size != sizeof(u64)) { + pr_err("Unable to get session header '%s' [%d]\n", + LUO_FDT_SESSION_HEADER, header_size); + return -EINVAL; + } + + header_ser_pa = get_unaligned((u64 *)ptr); + header_ser = phys_to_virt(header_ser_pa); + + luo_session_global.incoming.header_ser = header_ser; + luo_session_global.incoming.ser = (void *)(header_ser + 1); + INIT_LIST_HEAD(&luo_session_global.incoming.list); + init_rwsem(&luo_session_global.incoming.rwsem); + luo_session_global.incoming.active = true; + + return 0; +} + +bool luo_session_is_deserialized(void) +{ + return luo_session_global.deserialized; +} + +int luo_session_deserialize(void) +{ + struct luo_session_header *sh = &luo_session_global.incoming; + int err; + + if (luo_session_is_deserialized()) + return 0; + + luo_session_global.deserialized = true; + if (!sh->active) { + INIT_LIST_HEAD(&sh->list); + init_rwsem(&sh->rwsem); + return 0; + } + + for (int i = 0; i < sh->header_ser->count; i++) { + struct luo_session *session; + + session = luo_session_alloc(sh->ser[i].name); + if (IS_ERR(session)) { + pr_warn("Failed to allocate session [%s] during deserialization %pe\n", + sh->ser[i].name, session); + return PTR_ERR(session); + } + + err = luo_session_insert(sh, session); + if (err) { + luo_session_free(session); + pr_warn("Failed to insert session [%s] %pe\n", + session->name, ERR_PTR(err)); + return err; + } + + session->count = sh->ser[i].count; + session->files = sh->ser[i].files ? phys_to_virt(sh->ser[i].files) : 0; + session->pgcnt = sh->ser[i].pgcnt; + } + + kho_restore_free(sh->header_ser); + sh->header_ser = NULL; + sh->ser = NULL; + + return 0; +} + +int luo_session_serialize(void) +{ + struct luo_session_header *sh = &luo_session_global.outgoing; + struct luo_session *session; + int i = 0; + + guard(rwsem_write)(&sh->rwsem); + list_for_each_entry(session, &sh->list, list) { + strscpy(sh->ser[i].name, session->name, + sizeof(sh->ser[i].name)); + sh->ser[i].count = session->count; + sh->ser[i].files = session->files ? virt_to_phys(session->files) : 0; + sh->ser[i].pgcnt = session->pgcnt; + i++; + } + sh->header_ser->count = sh->count; + + return 0; +} -- 2.52.0.rc1.455.g30608eb744-goog