// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2017 - Cambridge Greys Ltd
 * Copyright (C) 2011 - 2014 Cisco Systems Inc
 * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
 * Derived (i.e. mostly copied) from arch/i386/kernel/irq.c:
 *      Copyright (C) 1992, 1998 Linus Torvalds, Ingo Molnar
 */

#include <linux/cpumask.h>
#include <linux/hardirq.h>
#include <linux/interrupt.h>
#include <linux/kernel_stat.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/seq_file.h>
#include <linux/slab.h>
#include <as-layout.h>
#include <kern_util.h>
#include <os.h>
#include <irq_user.h>
#include <irq_kern.h>
#include <linux/time-internal.h>


extern void free_irqs(void);

/* When epoll triggers we do not know why it did so
 * we can also have different IRQs for read and write.
 * This is why we keep a small irq_reg array for each fd -
 * one entry per IRQ type
 */
struct irq_reg {
        void *id;
        int irq;
        /* it's cheaper to store this than to query it */
        int events;
        bool active;
        bool pending;
        bool wakeup;
#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
        bool pending_on_resume;
        void (*timetravel_handler)(int, int, void *,
                                   struct time_travel_event *);
        struct time_travel_event event;
#endif
};

struct irq_entry {
        struct list_head list;
        int fd;
        struct irq_reg reg[NUM_IRQ_TYPES];
        bool suspended;
        bool sigio_workaround;
};

static DEFINE_SPINLOCK(irq_lock);
static LIST_HEAD(active_fds);
static DECLARE_BITMAP(irqs_allocated, UM_LAST_SIGNAL_IRQ);
static bool irqs_suspended;

static void irq_io_loop(struct irq_reg *irq, struct uml_pt_regs *regs)
{
/*
 * irq->active guards against reentry
 * irq->pending accumulates pending requests
 * if pending is raised the irq_handler is re-run
 * until pending is cleared
 */
        if (irq->active) {
                irq->active = false;

                do {
                        irq->pending = false;
                        do_IRQ(irq->irq, regs);
                } while (irq->pending);

                irq->active = true;
        } else {
                irq->pending = true;
        }
}

#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
static void irq_event_handler(struct time_travel_event *ev)
{
        struct irq_reg *reg = container_of(ev, struct irq_reg, event);

        /* do nothing if suspended - just to cause a wakeup */
        if (irqs_suspended)
                return;

        generic_handle_irq(reg->irq);
}

static bool irq_do_timetravel_handler(struct irq_entry *entry,
                                      enum um_irq_type t)
{
        struct irq_reg *reg = &entry->reg[t];

        if (!reg->timetravel_handler)
                return false;

        /*
         * Handle all messages - we might get multiple even while
         * interrupts are already suspended, due to suspend order
         * etc. Note that time_travel_add_irq_event() will not add
         * an event twice, if it's pending already "first wins".
         */
        reg->timetravel_handler(reg->irq, entry->fd, reg->id, &reg->event);

        if (!reg->event.pending)
                return false;

        if (irqs_suspended)
                reg->pending_on_resume = true;
        return true;
}
#else
static bool irq_do_timetravel_handler(struct irq_entry *entry,
                                      enum um_irq_type t)
{
        return false;
}
#endif

static void sigio_reg_handler(int idx, struct irq_entry *entry, enum um_irq_type t,
                              struct uml_pt_regs *regs,
                              bool timetravel_handlers_only)
{
        struct irq_reg *reg = &entry->reg[t];

        if (!reg->events)
                return;

        if (os_epoll_triggered(idx, reg->events) <= 0)
                return;

        if (irq_do_timetravel_handler(entry, t))
                return;

        /*
         * If we're called to only run time-travel handlers then don't
         * actually proceed but mark sigio as pending (if applicable).
         * For suspend/resume, timetravel_handlers_only may be true
         * despite time-travel not being configured and used.
         */
        if (timetravel_handlers_only) {
#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
                mark_sigio_pending();
#endif
                return;
        }

        irq_io_loop(reg, regs);
}

static void _sigio_handler(struct uml_pt_regs *regs,
                           bool timetravel_handlers_only)
{
        struct irq_entry *irq_entry;
        int n, i;

        if (timetravel_handlers_only && !um_irq_timetravel_handler_used())
                return;

        while (1) {
                /* This is now lockless - epoll keeps back-referencesto the irqs
                 * which have trigger it so there is no need to walk the irq
                 * list and lock it every time. We avoid locking by turning off
                 * IO for a specific fd by executing os_del_epoll_fd(fd) before
                 * we do any changes to the actual data structures
                 */
                n = os_waiting_for_events_epoll();

                if (n <= 0) {
                        if (n == -EINTR)
                                continue;
                        else
                                break;
                }

                for (i = 0; i < n ; i++) {
                        enum um_irq_type t;

                        irq_entry = os_epoll_get_data_pointer(i);

                        for (t = 0; t < NUM_IRQ_TYPES; t++)
                                sigio_reg_handler(i, irq_entry, t, regs,
                                                  timetravel_handlers_only);
                }
        }

        if (!timetravel_handlers_only)
                free_irqs();
}

void sigio_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
{
        _sigio_handler(regs, irqs_suspended);
}

static struct irq_entry *get_irq_entry_by_fd(int fd)
{
        struct irq_entry *walk;

        lockdep_assert_held(&irq_lock);

        list_for_each_entry(walk, &active_fds, list) {
                if (walk->fd == fd)
                        return walk;
        }

        return NULL;
}

static void free_irq_entry(struct irq_entry *to_free, bool remove)
{
        if (!to_free)
                return;

        if (remove)
                os_del_epoll_fd(to_free->fd);
        list_del(&to_free->list);
        kfree(to_free);
}

static bool update_irq_entry(struct irq_entry *entry)
{
        enum um_irq_type i;
        int events = 0;

        for (i = 0; i < NUM_IRQ_TYPES; i++)
                events |= entry->reg[i].events;

        if (events) {
                /* will modify (instead of add) if needed */
                os_add_epoll_fd(events, entry->fd, entry);
                return true;
        }

        os_del_epoll_fd(entry->fd);
        return false;
}

static void update_or_free_irq_entry(struct irq_entry *entry)
{
        if (!update_irq_entry(entry))
                free_irq_entry(entry, false);
}

static int activate_fd(int irq, int fd, enum um_irq_type type, void *dev_id,
                       void (*timetravel_handler)(int, int, void *,
                                                  struct time_travel_event *))
{
        struct irq_entry *irq_entry;
        int err, events = os_event_mask(type);
        unsigned long flags;

        err = os_set_fd_async(fd);
        if (err < 0)
                goto out;

        spin_lock_irqsave(&irq_lock, flags);
        irq_entry = get_irq_entry_by_fd(fd);
        if (irq_entry) {
                /* cannot register the same FD twice with the same type */
                if (WARN_ON(irq_entry->reg[type].events)) {
                        err = -EALREADY;
                        goto out_unlock;
                }

                /* temporarily disable to avoid IRQ-side locking */
                os_del_epoll_fd(fd);
        } else {
                irq_entry = kzalloc(sizeof(*irq_entry), GFP_ATOMIC);
                if (!irq_entry) {
                        err = -ENOMEM;
                        goto out_unlock;
                }
                irq_entry->fd = fd;
                list_add_tail(&irq_entry->list, &active_fds);
                maybe_sigio_broken(fd);
        }

        irq_entry->reg[type].id = dev_id;
        irq_entry->reg[type].irq = irq;
        irq_entry->reg[type].active = true;
        irq_entry->reg[type].events = events;

#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
        if (um_irq_timetravel_handler_used()) {
                irq_entry->reg[type].timetravel_handler = timetravel_handler;
                irq_entry->reg[type].event.fn = irq_event_handler;
        }
#endif

        WARN_ON(!update_irq_entry(irq_entry));
        spin_unlock_irqrestore(&irq_lock, flags);

        return 0;
out_unlock:
        spin_unlock_irqrestore(&irq_lock, flags);
out:
        return err;
}

/*
 * Remove the entry or entries for a specific FD, if you
 * don't want to remove all the possible entries then use
 * um_free_irq() or deactivate_fd() instead.
 */
void free_irq_by_fd(int fd)
{
        struct irq_entry *to_free;
        unsigned long flags;

        spin_lock_irqsave(&irq_lock, flags);
        to_free = get_irq_entry_by_fd(fd);
        free_irq_entry(to_free, true);
        spin_unlock_irqrestore(&irq_lock, flags);
}
EXPORT_SYMBOL(free_irq_by_fd);

static void free_irq_by_irq_and_dev(unsigned int irq, void *dev)
{
        struct irq_entry *entry;
        unsigned long flags;

        spin_lock_irqsave(&irq_lock, flags);
        list_for_each_entry(entry, &active_fds, list) {
                enum um_irq_type i;

                for (i = 0; i < NUM_IRQ_TYPES; i++) {
                        struct irq_reg *reg = &entry->reg[i];

                        if (!reg->events)
                                continue;
                        if (reg->irq != irq)
                                continue;
                        if (reg->id != dev)
                                continue;

                        os_del_epoll_fd(entry->fd);
                        reg->events = 0;
                        update_or_free_irq_entry(entry);
                        goto out;
                }
        }
out:
        spin_unlock_irqrestore(&irq_lock, flags);
}

void deactivate_fd(int fd, int irqnum)
{
        struct irq_entry *entry;
        unsigned long flags;
        enum um_irq_type i;

        os_del_epoll_fd(fd);

        spin_lock_irqsave(&irq_lock, flags);
        entry = get_irq_entry_by_fd(fd);
        if (!entry)
                goto out;

        for (i = 0; i < NUM_IRQ_TYPES; i++) {
                if (!entry->reg[i].events)
                        continue;
                if (entry->reg[i].irq == irqnum)
                        entry->reg[i].events = 0;
        }

        update_or_free_irq_entry(entry);
out:
        spin_unlock_irqrestore(&irq_lock, flags);

        ignore_sigio_fd(fd);
}
EXPORT_SYMBOL(deactivate_fd);

/*
 * Called just before shutdown in order to provide a clean exec
 * environment in case the system is rebooting.  No locking because
 * that would cause a pointless shutdown hang if something hadn't
 * released the lock.
 */
int deactivate_all_fds(void)
{
        struct irq_entry *entry;

        /* Stop IO. The IRQ loop has no lock so this is our
         * only way of making sure we are safe to dispose
         * of all IRQ handlers
         */
        os_set_ioignore();

        /* we can no longer call kfree() here so just deactivate */
        list_for_each_entry(entry, &active_fds, list)
                os_del_epoll_fd(entry->fd);
        os_close_epoll_fd();
        return 0;
}

/*
 * do_IRQ handles all normal device IRQs (the special
 * SMP cross-CPU interrupts have their own specific
 * handlers).
 */
unsigned int do_IRQ(int irq, struct uml_pt_regs *regs)
{
        struct pt_regs *old_regs = set_irq_regs((struct pt_regs *)regs);
        irq_enter();
        generic_handle_irq(irq);
        irq_exit();
        set_irq_regs(old_regs);
        return 1;
}

void um_free_irq(int irq, void *dev)
{
        if (WARN(irq < 0 || irq > UM_LAST_SIGNAL_IRQ,
                 "freeing invalid irq %d", irq))
                return;

        free_irq_by_irq_and_dev(irq, dev);
        free_irq(irq, dev);
        clear_bit(irq, irqs_allocated);
}
EXPORT_SYMBOL(um_free_irq);

static int
_um_request_irq(int irq, int fd, enum um_irq_type type,
                irq_handler_t handler, unsigned long irqflags,
                const char *devname, void *dev_id,
                void (*timetravel_handler)(int, int, void *,
                                           struct time_travel_event *))
{
        int err;

        if (irq == UM_IRQ_ALLOC) {
                int i;

                for (i = UM_FIRST_DYN_IRQ; i < NR_IRQS; i++) {
                        if (!test_and_set_bit(i, irqs_allocated)) {
                                irq = i;
                                break;
                        }
                }
        }

        if (irq < 0)
                return -ENOSPC;

        if (fd != -1) {
                err = activate_fd(irq, fd, type, dev_id, timetravel_handler);
                if (err)
                        goto error;
        }

        err = request_irq(irq, handler, irqflags, devname, dev_id);
        if (err < 0)
                goto error;

        return irq;
error:
        clear_bit(irq, irqs_allocated);
        return err;
}

int um_request_irq(int irq, int fd, enum um_irq_type type,
                   irq_handler_t handler, unsigned long irqflags,
                   const char *devname, void *dev_id)
{
        return _um_request_irq(irq, fd, type, handler, irqflags,
                               devname, dev_id, NULL);
}
EXPORT_SYMBOL(um_request_irq);

#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
int um_request_irq_tt(int irq, int fd, enum um_irq_type type,
                      irq_handler_t handler, unsigned long irqflags,
                      const char *devname, void *dev_id,
                      void (*timetravel_handler)(int, int, void *,
                                                 struct time_travel_event *))
{
        return _um_request_irq(irq, fd, type, handler, irqflags,
                               devname, dev_id, timetravel_handler);
}
EXPORT_SYMBOL(um_request_irq_tt);

void sigio_run_timetravel_handlers(void)
{
        _sigio_handler(NULL, true);
}
#endif

#ifdef CONFIG_PM_SLEEP
void um_irqs_suspend(void)
{
        struct irq_entry *entry;
        unsigned long flags;

        irqs_suspended = true;

        spin_lock_irqsave(&irq_lock, flags);
        list_for_each_entry(entry, &active_fds, list) {
                enum um_irq_type t;
                bool clear = true;

                for (t = 0; t < NUM_IRQ_TYPES; t++) {
                        if (!entry->reg[t].events)
                                continue;

                        /*
                         * For the SIGIO_WRITE_IRQ, which is used to handle the
                         * SIGIO workaround thread, we need special handling:
                         * enable wake for it itself, but below we tell it about
                         * any FDs that should be suspended.
                         */
                        if (entry->reg[t].wakeup ||
                            entry->reg[t].irq == SIGIO_WRITE_IRQ
#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
                            || entry->reg[t].timetravel_handler
#endif
                            ) {
                                clear = false;
                                break;
                        }
                }

                if (clear) {
                        entry->suspended = true;
                        os_clear_fd_async(entry->fd);
                        entry->sigio_workaround =
                                !__ignore_sigio_fd(entry->fd);
                }
        }
        spin_unlock_irqrestore(&irq_lock, flags);
}

void um_irqs_resume(void)
{
        struct irq_entry *entry;
        unsigned long flags;


        local_irq_save(flags);
#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
        /*
         * We don't need to lock anything here since we're in resume
         * and nothing else is running, but have disabled IRQs so we
         * don't try anything else with the interrupt list from there.
         */
        list_for_each_entry(entry, &active_fds, list) {
                enum um_irq_type t;

                for (t = 0; t < NUM_IRQ_TYPES; t++) {
                        struct irq_reg *reg = &entry->reg[t];

                        if (reg->pending_on_resume) {
                                irq_enter();
                                generic_handle_irq(reg->irq);
                                irq_exit();
                                reg->pending_on_resume = false;
                        }
                }
        }
#endif

        spin_lock(&irq_lock);
        list_for_each_entry(entry, &active_fds, list) {
                if (entry->suspended) {
                        int err = os_set_fd_async(entry->fd);

                        WARN(err < 0, "os_set_fd_async returned %d\n", err);
                        entry->suspended = false;

                        if (entry->sigio_workaround) {
                                err = __add_sigio_fd(entry->fd);
                                WARN(err < 0, "add_sigio_returned %d\n", err);
                        }
                }
        }
        spin_unlock_irqrestore(&irq_lock, flags);

        irqs_suspended = false;
        send_sigio_to_self();
}

static int normal_irq_set_wake(struct irq_data *d, unsigned int on)
{
        struct irq_entry *entry;
        unsigned long flags;

        spin_lock_irqsave(&irq_lock, flags);
        list_for_each_entry(entry, &active_fds, list) {
                enum um_irq_type t;

                for (t = 0; t < NUM_IRQ_TYPES; t++) {
                        if (!entry->reg[t].events)
                                continue;

                        if (entry->reg[t].irq != d->irq)
                                continue;
                        entry->reg[t].wakeup = on;
                        goto unlock;
                }
        }
unlock:
        spin_unlock_irqrestore(&irq_lock, flags);
        return 0;
}
#else
#define normal_irq_set_wake NULL
#endif

/*
 * irq_chip must define at least enable/disable and ack when
 * the edge handler is used.
 */
static void dummy(struct irq_data *d)
{
}

/* This is used for everything other than the timer. */
static struct irq_chip normal_irq_type = {
        .name = "SIGIO",
        .irq_disable = dummy,
        .irq_enable = dummy,
        .irq_ack = dummy,
        .irq_mask = dummy,
        .irq_unmask = dummy,
        .irq_set_wake = normal_irq_set_wake,
};

static struct irq_chip alarm_irq_type = {
        .name = "SIGALRM",
        .irq_disable = dummy,
        .irq_enable = dummy,
        .irq_ack = dummy,
        .irq_mask = dummy,
        .irq_unmask = dummy,
};

void __init init_IRQ(void)
{
        int i;

        irq_set_chip_and_handler(TIMER_IRQ, &alarm_irq_type, handle_edge_irq);

        for (i = 1; i < UM_LAST_SIGNAL_IRQ; i++)
                irq_set_chip_and_handler(i, &normal_irq_type, handle_edge_irq);
        /* Initialize EPOLL Loop */
        os_setup_epoll();
}

/*
 * IRQ stack entry and exit:
 *
 * Unlike i386, UML doesn't receive IRQs on the normal kernel stack
 * and switch over to the IRQ stack after some preparation.  We use
 * sigaltstack to receive signals on a separate stack from the start.
 * These two functions make sure the rest of the kernel won't be too
 * upset by being on a different stack.  The IRQ stack has a
 * thread_info structure at the bottom so that current et al continue
 * to work.
 *
 * to_irq_stack copies the current task's thread_info to the IRQ stack
 * thread_info and sets the tasks's stack to point to the IRQ stack.
 *
 * from_irq_stack copies the thread_info struct back (flags may have
 * been modified) and resets the task's stack pointer.
 *
 * Tricky bits -
 *
 * What happens when two signals race each other?  UML doesn't block
 * signals with sigprocmask, SA_DEFER, or sa_mask, so a second signal
 * could arrive while a previous one is still setting up the
 * thread_info.
 *
 * There are three cases -
 *     The first interrupt on the stack - sets up the thread_info and
 * handles the interrupt
 *     A nested interrupt interrupting the copying of the thread_info -
 * can't handle the interrupt, as the stack is in an unknown state
 *     A nested interrupt not interrupting the copying of the
 * thread_info - doesn't do any setup, just handles the interrupt
 *
 * The first job is to figure out whether we interrupted stack setup.
 * This is done by xchging the signal mask with thread_info->pending.
 * If the value that comes back is zero, then there is no setup in
 * progress, and the interrupt can be handled.  If the value is
 * non-zero, then there is stack setup in progress.  In order to have
 * the interrupt handled, we leave our signal in the mask, and it will
 * be handled by the upper handler after it has set up the stack.
 *
 * Next is to figure out whether we are the outer handler or a nested
 * one.  As part of setting up the stack, thread_info->real_thread is
 * set to non-NULL (and is reset to NULL on exit).  This is the
 * nesting indicator.  If it is non-NULL, then the stack is already
 * set up and the handler can run.
 */

static unsigned long pending_mask;

unsigned long to_irq_stack(unsigned long *mask_out)
{
        struct thread_info *ti;
        unsigned long mask, old;
        int nested;

        mask = xchg(&pending_mask, *mask_out);
        if (mask != 0) {
                /*
                 * If any interrupts come in at this point, we want to
                 * make sure that their bits aren't lost by our
                 * putting our bit in.  So, this loop accumulates bits
                 * until xchg returns the same value that we put in.
                 * When that happens, there were no new interrupts,
                 * and pending_mask contains a bit for each interrupt
                 * that came in.
                 */
                old = *mask_out;
                do {
                        old |= mask;
                        mask = xchg(&pending_mask, old);
                } while (mask != old);
                return 1;
        }

        ti = current_thread_info();
        nested = (ti->real_thread != NULL);
        if (!nested) {
                struct task_struct *task;
                struct thread_info *tti;

                task = cpu_tasks[ti->cpu].task;
                tti = task_thread_info(task);

                *ti = *tti;
                ti->real_thread = tti;
                task->stack = ti;
        }

        mask = xchg(&pending_mask, 0);
        *mask_out |= mask | nested;
        return 0;
}

unsigned long from_irq_stack(int nested)
{
        struct thread_info *ti, *to;
        unsigned long mask;

        ti = current_thread_info();

        pending_mask = 1;

        to = ti->real_thread;
        current->stack = to;
        ti->real_thread = NULL;
        *to = *ti;

        mask = xchg(&pending_mask, 0);
        return mask & ~1;
}