// SPDX-License-Identifier: GPL-2.0

/*
 * Copyright (c) 2025, Google LLC.
 * Pasha Tatashin <pasha.tatashin@soleen.com>
 */

/**
 * DOC: Live Update Orchestrator (LUO)
 *
 * Live Update is a specialized, kexec-based reboot process that allows a
 * running kernel to be updated from one version to another while preserving
 * the state of selected resources and keeping designated hardware devices
 * operational. For these devices, DMA activity may continue throughout the
 * kernel transition.
 *
 * While the primary use case driving this work is supporting live updates of
 * the Linux kernel when it is used as a hypervisor in cloud environments, the
 * LUO framework itself is designed to be workload-agnostic. Live Update
 * facilitates a full kernel version upgrade for any type of system.
 *
 * For example, a non-hypervisor system running an in-memory cache like
 * memcached with many gigabytes of data can use LUO. The userspace service
 * can place its cache into a memfd, have its state preserved by LUO, and
 * restore it immediately after the kernel kexec.
 *
 * Whether the system is running virtual machines, containers, a
 * high-performance database, or networking services, LUO's primary goal is to
 * enable a full kernel update by preserving critical userspace state and
 * keeping essential devices operational.
 *
 * The core of LUO is a mechanism that tracks the progress of a live update,
 * along with a callback API that allows other kernel subsystems to participate
 * in the process. Example subsystems that can hook into LUO include: kvm,
 * iommu, interrupts, vfio, participating filesystems, and memory management.
 *
 * LUO uses Kexec Handover to transfer memory state from the current kernel to
 * the next kernel. For more details see Documentation/core-api/kho/index.rst.
 *
 * .. note::
 *     To enable LUO, boot the kernel with the ``liveupdate=on`` command line
 *     parameter.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/atomic.h>
#include <linux/errno.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/io.h>
#include <linux/kernel.h>
#include <linux/kexec_handover.h>
#include <linux/kho/abi/luo.h>
#include <linux/kobject.h>
#include <linux/liveupdate.h>
#include <linux/miscdevice.h>
#include <linux/mm.h>
#include <linux/rwsem.h>
#include <linux/sizes.h>
#include <linux/string.h>

#include "kexec_handover_internal.h"
#include "luo_internal.h"

static struct {
        bool enabled;
        struct luo_ser *luo_ser_out;
        u64 liveupdate_num;
} luo_global;

/*
 * luo_register_rwlock - Protects registration of file handlers and FLBs.
 */
DECLARE_RWSEM(luo_register_rwlock);

static int __init early_liveupdate_param(char *buf)
{
        return kstrtobool(buf, &luo_global.enabled);
}
early_param("liveupdate", early_liveupdate_param);

static int __init luo_early_startup(void)
{
        phys_addr_t luo_ser_phys;
        struct luo_ser *luo_ser;
        size_t len;
        int err;

        if (!kho_is_enabled()) {
                if (liveupdate_enabled())
                        pr_warn("Disabling liveupdate because KHO is disabled\n");
                luo_global.enabled = false;
                return 0;
        }

        /* Retrieve LUO state from KHO. */
        err = kho_retrieve_subtree(LUO_KHO_ENTRY_NAME, &luo_ser_phys, &len);
        if (err) {
                if (err != -ENOENT) {
                        pr_err("failed to retrieve LUO state '%s' from KHO: %pe\n",
                               LUO_KHO_ENTRY_NAME, ERR_PTR(err));
                        return err;
                }

                return 0;
        }

        if (len < sizeof(*luo_ser)) {
                pr_err("LUO state is too small (%zu < %zu)\n", len, sizeof(*luo_ser));
                return -EINVAL;
        }

        luo_ser = phys_to_virt(luo_ser_phys);
        if (strncmp(luo_ser->compatible, LUO_ABI_COMPATIBLE, LUO_ABI_COMPAT_LEN)) {
                pr_err("LUO state is incompatible with '%s'\n", LUO_ABI_COMPATIBLE);
                return -EINVAL;
        }

        luo_global.liveupdate_num = luo_ser->liveupdate_num;
        pr_info("Retrieved live update data, liveupdate number: %lld\n",
                luo_global.liveupdate_num);

        err = luo_session_setup_incoming(luo_ser->sessions_pa);
        if (err)
                goto out_free_ser;

        luo_flb_setup_incoming(luo_ser->flbs_pa);

        err = 0;

out_free_ser:
        kho_restore_free(luo_ser);
        return err;
}

static int __init liveupdate_early_init(void)
{
        int err;

        err = luo_early_startup();
        if (err) {
                luo_global.enabled = false;
                luo_restore_fail("The incoming tree failed to initialize properly [%pe], disabling live update\n",
                                 ERR_PTR(err));
        }

        return err;
}
early_initcall(liveupdate_early_init);

/* Called during boot to create outgoing LUO state */
static int __init luo_state_setup(void)
{
        struct luo_ser *luo_ser;
        int err;

        luo_ser = kho_alloc_preserve(sizeof(*luo_ser));
        if (IS_ERR(luo_ser)) {
                pr_err("failed to allocate/preserve LUO state memory\n");
                return PTR_ERR(luo_ser);
        }

        strscpy(luo_ser->compatible, LUO_ABI_COMPATIBLE, sizeof(luo_ser->compatible));
        luo_ser->liveupdate_num = luo_global.liveupdate_num + 1;

        luo_session_setup_outgoing(&luo_ser->sessions_pa);

        err = luo_flb_setup_outgoing(&luo_ser->flbs_pa);
        if (err)
                goto exit_free_luo_ser;

        err = kho_add_subtree(LUO_KHO_ENTRY_NAME, luo_ser, sizeof(*luo_ser));
        if (err)
                goto exit_free_luo_ser;

        luo_global.luo_ser_out = luo_ser;

        return 0;

exit_free_luo_ser:
        kho_unpreserve_free(luo_ser);
        pr_err("failed to prepare LUO state: %d\n", err);

        return err;
}

/*
 * late initcall because it initializes the outgoing tree that is needed only
 * once userspace starts using /dev/liveupdate.
 */
static int __init luo_late_startup(void)
{
        int err;

        if (!liveupdate_enabled())
                return 0;

        err = luo_state_setup();
        if (err)
                luo_global.enabled = false;

        return err;
}
late_initcall(luo_late_startup);

/* Public Functions */

/**
 * liveupdate_reboot() - Kernel reboot notifier for live update final
 * serialization.
 *
 * This function is invoked directly from the reboot() syscall pathway
 * if kexec is in progress.
 *
 * If any callback fails, this function aborts KHO, undoes the freeze()
 * callbacks, and returns an error.
 */
int liveupdate_reboot(void)
{
        int err;

        if (!liveupdate_enabled())
                return 0;

        err = luo_session_serialize();
        if (err)
                return err;

        luo_flb_serialize();

        return 0;
}

/**
 * liveupdate_enabled - Check if the live update feature is enabled.
 *
 * This function returns the state of the live update feature flag, which
 * can be controlled via the ``liveupdate`` kernel command-line parameter.
 *
 * @return true if live update is enabled, false otherwise.
 */
bool liveupdate_enabled(void)
{
        return luo_global.enabled;
}

/**
 * DOC: LUO ioctl Interface
 *
 * The IOCTL user-space control interface for the LUO subsystem.
 * It registers a character device, typically found at ``/dev/liveupdate``,
 * which allows a userspace agent to manage the LUO state machine and its
 * associated resources, such as preservable file descriptors.
 *
 * To ensure that the state machine is controlled by a single entity, access
 * to this device is exclusive: only one process is permitted to have
 * ``/dev/liveupdate`` open at any given time. Subsequent open attempts will
 * fail with -EBUSY until the first process closes its file descriptor.
 * This singleton model simplifies state management by preventing conflicting
 * commands from multiple userspace agents.
 */

struct luo_device_state {
        struct miscdevice miscdev;
        atomic_t in_use;
};

static int luo_ioctl_create_session(struct luo_ucmd *ucmd)
{
        struct liveupdate_ioctl_create_session *argp = ucmd->cmd;
        struct file *file;
        int err;

        argp->fd = get_unused_fd_flags(O_CLOEXEC);
        if (argp->fd < 0)
                return argp->fd;

        err = luo_session_create(argp->name, &file);
        if (err)
                goto err_put_fd;

        err = luo_ucmd_respond(ucmd, sizeof(*argp));
        if (err)
                goto err_put_file;

        fd_install(argp->fd, file);

        return 0;

err_put_file:
        fput(file);
err_put_fd:
        put_unused_fd(argp->fd);

        return err;
}

static int luo_ioctl_retrieve_session(struct luo_ucmd *ucmd)
{
        struct liveupdate_ioctl_retrieve_session *argp = ucmd->cmd;
        struct file *file;
        int err;

        argp->fd = get_unused_fd_flags(O_CLOEXEC);
        if (argp->fd < 0)
                return argp->fd;

        err = luo_session_retrieve(argp->name, &file);
        if (err < 0)
                goto err_put_fd;

        err = luo_ucmd_respond(ucmd, sizeof(*argp));
        if (err)
                goto err_put_file;

        fd_install(argp->fd, file);

        return 0;

err_put_file:
        fput(file);
err_put_fd:
        put_unused_fd(argp->fd);

        return err;
}

static int luo_open(struct inode *inodep, struct file *filep)
{
        struct luo_device_state *ldev = container_of(filep->private_data,
                                                     struct luo_device_state,
                                                     miscdev);

        if (atomic_cmpxchg(&ldev->in_use, 0, 1))
                return -EBUSY;

        /* Always return -EIO to user if deserialization fail */
        if (luo_session_deserialize()) {
                atomic_set(&ldev->in_use, 0);
                return -EIO;
        }

        return 0;
}

static int luo_release(struct inode *inodep, struct file *filep)
{
        struct luo_device_state *ldev = container_of(filep->private_data,
                                                     struct luo_device_state,
                                                     miscdev);
        atomic_set(&ldev->in_use, 0);

        return 0;
}

union ucmd_buffer {
        struct liveupdate_ioctl_create_session create;
        struct liveupdate_ioctl_retrieve_session retrieve;
};

struct luo_ioctl_op {
        unsigned int size;
        unsigned int min_size;
        unsigned int ioctl_num;
        int (*execute)(struct luo_ucmd *ucmd);
};

#define IOCTL_OP(_ioctl, _fn, _struct, _last)                                  \
        [_IOC_NR(_ioctl) - LIVEUPDATE_CMD_BASE] = {                            \
                .size = sizeof(_struct) +                                      \
                        BUILD_BUG_ON_ZERO(sizeof(union ucmd_buffer) <          \
                                          sizeof(_struct)),                    \
                .min_size = offsetofend(_struct, _last),                       \
                .ioctl_num = _ioctl,                                           \
                .execute = _fn,                                                \
        }

static const struct luo_ioctl_op luo_ioctl_ops[] = {
        IOCTL_OP(LIVEUPDATE_IOCTL_CREATE_SESSION, luo_ioctl_create_session,
                 struct liveupdate_ioctl_create_session, name),
        IOCTL_OP(LIVEUPDATE_IOCTL_RETRIEVE_SESSION, luo_ioctl_retrieve_session,
                 struct liveupdate_ioctl_retrieve_session, name),
};

static long luo_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
{
        const struct luo_ioctl_op *op;
        struct luo_ucmd ucmd = {};
        union ucmd_buffer buf;
        unsigned int nr;
        int err;

        nr = _IOC_NR(cmd);
        if (nr - LIVEUPDATE_CMD_BASE >= ARRAY_SIZE(luo_ioctl_ops))
                return -EINVAL;

        ucmd.ubuffer = (void __user *)arg;
        err = get_user(ucmd.user_size, (u32 __user *)ucmd.ubuffer);
        if (err)
                return err;

        op = &luo_ioctl_ops[nr - LIVEUPDATE_CMD_BASE];
        if (op->ioctl_num != cmd)
                return -ENOIOCTLCMD;
        if (ucmd.user_size < op->min_size)
                return -EINVAL;

        ucmd.cmd = &buf;
        err = copy_struct_from_user(ucmd.cmd, op->size, ucmd.ubuffer,
                                    ucmd.user_size);
        if (err)
                return err;

        return op->execute(&ucmd);
}

static const struct file_operations luo_fops = {
        .owner          = THIS_MODULE,
        .open           = luo_open,
        .release        = luo_release,
        .unlocked_ioctl = luo_ioctl,
};

static struct luo_device_state luo_dev = {
        .miscdev = {
                .minor = MISC_DYNAMIC_MINOR,
                .name  = "liveupdate",
                .fops  = &luo_fops,
        },
        .in_use = ATOMIC_INIT(0),
};

static int __init liveupdate_ioctl_init(void)
{
        if (!liveupdate_enabled())
                return 0;

        return misc_register(&luo_dev.miscdev);
}
late_initcall(liveupdate_ioctl_init);