// SPDX-License-Identifier: GPL-2.0
/*
 * ACRN HSM irqfd: use eventfd objects to inject virtual interrupts
 *
 * Copyright (C) 2020 Intel Corporation. All rights reserved.
 *
 * Authors:
 *      Shuo Liu <shuo.a.liu@intel.com>
 *      Yakui Zhao <yakui.zhao@intel.com>
 */

#include <linux/eventfd.h>
#include <linux/file.h>
#include <linux/poll.h>
#include <linux/slab.h>

#include "acrn_drv.h"

/* Cleanup work has been queued; set via test_and_set_bit(). */
#define HSM_IRQFD_FLAG_SHUTDOWN 0

/**
 * struct hsm_irqfd - Properties of HSM irqfd
 * @vm:         Associated VM pointer
 * @wait:       Entry of wait-queue
 * @shutdown:   Async shutdown work
 * @eventfd:    Associated eventfd
 * @list:       Entry within &acrn_vm.irqfds of irqfds of a VM
 * @pt:         Structure for select/poll on the associated eventfd
 * @msi:        MSI data
 * @flags:      Internal lifecycle flags (HSM_IRQFD_FLAG_*)
 */
struct hsm_irqfd {
        struct acrn_vm          *vm;
        wait_queue_entry_t      wait;
        struct work_struct      shutdown;
        struct eventfd_ctx      *eventfd;
        struct list_head        list;
        poll_table              pt;
        struct acrn_msi_entry   msi;
        unsigned long           flags;
};

static void acrn_irqfd_inject(struct hsm_irqfd *irqfd)
{
        struct acrn_vm *vm = irqfd->vm;

        acrn_msi_inject(vm, irqfd->msi.msi_addr,
                        irqfd->msi.msi_data);
}

/* Queue the cleanup work at most once. Safe from atomic context. */
static void hsm_irqfd_queue_shutdown(struct hsm_irqfd *irqfd)
{
        if (!test_and_set_bit(HSM_IRQFD_FLAG_SHUTDOWN, &irqfd->flags))
                queue_work(irqfd->vm->irqfd_wq, &irqfd->shutdown);
}

/* Sole owner of @irqfd: unhook waitqueue, drop eventfd ref, free. */
static void hsm_irqfd_shutdown_work(struct work_struct *work)
{
        struct hsm_irqfd *irqfd = container_of(work, struct hsm_irqfd,
                                               shutdown);
        struct acrn_vm *vm = irqfd->vm;
        u64 cnt;

        mutex_lock(&vm->irqfds_lock);
        if (!list_empty(&irqfd->list))
                list_del_init(&irqfd->list);
        mutex_unlock(&vm->irqfds_lock);

        eventfd_ctx_remove_wait_queue(irqfd->eventfd, &irqfd->wait, &cnt);
        eventfd_ctx_put(irqfd->eventfd);
        kfree(irqfd);
}

/* Called with wqh->lock held and interrupts disabled */
static int hsm_irqfd_wakeup(wait_queue_entry_t *wait, unsigned int mode,
                            int sync, void *key)
{
        unsigned long poll_bits = (unsigned long)key;
        struct hsm_irqfd *irqfd;

        irqfd = container_of(wait, struct hsm_irqfd, wait);

        if (poll_bits & POLLIN)
                /* An event has been signaled, inject an interrupt */
                acrn_irqfd_inject(irqfd);

        if (poll_bits & POLLHUP)
                /* Defer teardown to the cleanup work; can't sleep here. */
                hsm_irqfd_queue_shutdown(irqfd);

        return 0;
}

static void hsm_irqfd_poll_func(struct file *file, wait_queue_head_t *wqh,
                                poll_table *pt)
{
        struct hsm_irqfd *irqfd;

        irqfd = container_of(pt, struct hsm_irqfd, pt);
        add_wait_queue(wqh, &irqfd->wait);
}

/*
 * Assign an eventfd to a VM and create a HSM irqfd associated with the
 * eventfd. The properties of the HSM irqfd are built from a &struct
 * acrn_irqfd.
 */
static int acrn_irqfd_assign(struct acrn_vm *vm, struct acrn_irqfd *args)
{
        struct eventfd_ctx *eventfd = NULL;
        struct hsm_irqfd *irqfd, *tmp;
        __poll_t events;
        int ret = 0;

        irqfd = kzalloc_obj(*irqfd);
        if (!irqfd)
                return -ENOMEM;

        irqfd->vm = vm;
        memcpy(&irqfd->msi, &args->msi, sizeof(args->msi));
        INIT_LIST_HEAD(&irqfd->list);
        INIT_WORK(&irqfd->shutdown, hsm_irqfd_shutdown_work);

        CLASS(fd, f)(args->fd);
        if (fd_empty(f)) {
                ret = -EBADF;
                goto out;
        }

        eventfd = eventfd_ctx_fileget(fd_file(f));
        if (IS_ERR(eventfd)) {
                ret = PTR_ERR(eventfd);
                goto out;
        }

        irqfd->eventfd = eventfd;

        /*
         * Install custom wake-up handling to be notified whenever underlying
         * eventfd is signaled.
         */
        init_waitqueue_func_entry(&irqfd->wait, hsm_irqfd_wakeup);
        init_poll_funcptr(&irqfd->pt, hsm_irqfd_poll_func);

        /*
         * Hold irqfds_lock across waitqueue install and list_add so the
         * irqfd is not visible to deassign/deinit before its waitqueue
         * entry is in place, and any racing EPOLLHUP cleanup work blocks
         * on irqfds_lock until publication completes.
         */
        mutex_lock(&vm->irqfds_lock);
        list_for_each_entry(tmp, &vm->irqfds, list) {
                if (irqfd->eventfd != tmp->eventfd)
                        continue;
                ret = -EBUSY;
                mutex_unlock(&vm->irqfds_lock);
                goto fail;
        }

        events = vfs_poll(fd_file(f), &irqfd->pt);
        list_add_tail(&irqfd->list, &vm->irqfds);
        if (events & EPOLLIN)
                acrn_irqfd_inject(irqfd);
        mutex_unlock(&vm->irqfds_lock);

        return 0;
fail:
        eventfd_ctx_put(eventfd);
out:
        kfree(irqfd);
        return ret;
}

static int acrn_irqfd_deassign(struct acrn_vm *vm,
                               struct acrn_irqfd *args)
{
        struct hsm_irqfd *irqfd, *tmp;
        struct eventfd_ctx *eventfd;

        eventfd = eventfd_ctx_fdget(args->fd);
        if (IS_ERR(eventfd))
                return PTR_ERR(eventfd);

        mutex_lock(&vm->irqfds_lock);
        list_for_each_entry_safe(irqfd, tmp, &vm->irqfds, list) {
                if (irqfd->eventfd == eventfd) {
                        list_del_init(&irqfd->list);
                        hsm_irqfd_queue_shutdown(irqfd);
                        break;
                }
        }
        mutex_unlock(&vm->irqfds_lock);
        eventfd_ctx_put(eventfd);

        /* Wait for cleanup work to finish so the eventfd is fully detached. */
        flush_workqueue(vm->irqfd_wq);

        return 0;
}

int acrn_irqfd_config(struct acrn_vm *vm, struct acrn_irqfd *args)
{
        int ret;

        if (args->flags & ACRN_IRQFD_FLAG_DEASSIGN)
                ret = acrn_irqfd_deassign(vm, args);
        else
                ret = acrn_irqfd_assign(vm, args);

        return ret;
}

int acrn_irqfd_init(struct acrn_vm *vm)
{
        INIT_LIST_HEAD(&vm->irqfds);
        mutex_init(&vm->irqfds_lock);
        vm->irqfd_wq = alloc_workqueue("acrn_irqfd-%u", WQ_PERCPU, 0, vm->vmid);
        if (!vm->irqfd_wq)
                return -ENOMEM;

        dev_dbg(acrn_dev.this_device, "VM %u irqfd init.\n", vm->vmid);
        return 0;
}

void acrn_irqfd_deinit(struct acrn_vm *vm)
{
        struct hsm_irqfd *irqfd, *next;

        dev_dbg(acrn_dev.this_device, "VM %u irqfd deinit.\n", vm->vmid);

        mutex_lock(&vm->irqfds_lock);
        list_for_each_entry_safe(irqfd, next, &vm->irqfds, list) {
                list_del_init(&irqfd->list);
                hsm_irqfd_queue_shutdown(irqfd);
        }
        mutex_unlock(&vm->irqfds_lock);

        /* Drain all cleanup work before tearing the workqueue down. */
        flush_workqueue(vm->irqfd_wq);
        destroy_workqueue(vm->irqfd_wq);
}