drivers/vfio/virqfd.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * VFIO generic eventfd code for IRQFD support.
   4  * Derived from drivers/vfio/pci/vfio_pci_intrs.c
   5  *
   6  * Copyright (C) 2012 Red Hat, Inc.  All rights reserved.
   7  *     Author: Alex Williamson <alex.williamson@redhat.com>
   8  */
   9
  10 #include <linux/vfio.h>
  11 #include <linux/eventfd.h>
  12 #include <linux/file.h>
  13 #include <linux/module.h>
  14 #include <linux/slab.h>
  15
  16 #define DRIVER_VERSION  "0.1"
  17 #define DRIVER_AUTHOR   "Alex Williamson <alex.williamson@redhat.com>"
  18 #define DRIVER_DESC     "IRQFD support for VFIO bus drivers"
  19
  20 static struct workqueue_struct *vfio_irqfd_cleanup_wq;
  21 static DEFINE_SPINLOCK(virqfd_lock);
  22
  23 static int __init vfio_virqfd_init(void)
  24 {
  25         vfio_irqfd_cleanup_wq =
  26                 create_singlethread_workqueue("vfio-irqfd-cleanup");
  27         if (!vfio_irqfd_cleanup_wq)
  28                 return -ENOMEM;
  29
  30         return 0;
  31 }
  32
  33 static void __exit vfio_virqfd_exit(void)
  34 {
  35         destroy_workqueue(vfio_irqfd_cleanup_wq);
  36 }
  37
  38 static void virqfd_deactivate(struct virqfd *virqfd)
  39 {
  40         queue_work(vfio_irqfd_cleanup_wq, &virqfd->shutdown);
  41 }
  42
  43 static int virqfd_wakeup(wait_queue_entry_t *wait, unsigned mode, int sync, void *key)
  44 {
  45         struct virqfd *virqfd = container_of(wait, struct virqfd, wait);
  46         __poll_t flags = key_to_poll(key);
  47
  48         if (flags & EPOLLIN) {
  49                 /* An event has been signaled, call function */
  50                 if ((!virqfd->handler ||
  51                      virqfd->handler(virqfd->opaque, virqfd->data)) &&
  52                     virqfd->thread)
  53                         schedule_work(&virqfd->inject);
  54         }
  55
  56         if (flags & EPOLLHUP) {
  57                 unsigned long flags;
  58                 spin_lock_irqsave(&virqfd_lock, flags);
  59
  60                 /*
  61                  * The eventfd is closing, if the virqfd has not yet been
  62                  * queued for release, as determined by testing whether the
  63                  * virqfd pointer to it is still valid, queue it now.  As
  64                  * with kvm irqfds, we know we won't race against the virqfd
  65                  * going away because we hold the lock to get here.
  66                  */
  67                 if (*(virqfd->pvirqfd) == virqfd) {
  68                         *(virqfd->pvirqfd) = NULL;
  69                         virqfd_deactivate(virqfd);
  70                 }
  71
  72                 spin_unlock_irqrestore(&virqfd_lock, flags);
  73         }
  74
  75         return 0;
  76 }
  77
  78 static void virqfd_ptable_queue_proc(struct file *file,
  79                                      wait_queue_head_t *wqh, poll_table *pt)
  80 {
  81         struct virqfd *virqfd = container_of(pt, struct virqfd, pt);
  82         add_wait_queue(wqh, &virqfd->wait);
  83 }
  84
  85 static void virqfd_shutdown(struct work_struct *work)
  86 {
  87         struct virqfd *virqfd = container_of(work, struct virqfd, shutdown);
  88         u64 cnt;
  89
  90         eventfd_ctx_remove_wait_queue(virqfd->eventfd, &virqfd->wait, &cnt);
  91         flush_work(&virqfd->inject);
  92         eventfd_ctx_put(virqfd->eventfd);
  93
  94         kfree(virqfd);
  95 }
  96
  97 static void virqfd_inject(struct work_struct *work)
  98 {
  99         struct virqfd *virqfd = container_of(work, struct virqfd, inject);
 100         if (virqfd->thread)
 101                 virqfd->thread(virqfd->opaque, virqfd->data);
 102 }
 103
 104 int vfio_virqfd_enable(void *opaque,
 105                        int (*handler)(void *, void *),
 106                        void (*thread)(void *, void *),
 107                        void *data, struct virqfd **pvirqfd, int fd)
 108 {
 109         struct fd irqfd;
 110         struct eventfd_ctx *ctx;
 111         struct virqfd *virqfd;
 112         int ret = 0;
 113         __poll_t events;
 114
 115         virqfd = kzalloc(sizeof(*virqfd), GFP_KERNEL);
 116         if (!virqfd)
 117                 return -ENOMEM;
 118
 119         virqfd->pvirqfd = pvirqfd;
 120         virqfd->opaque = opaque;
 121         virqfd->handler = handler;
 122         virqfd->thread = thread;
 123         virqfd->data = data;
 124
 125         INIT_WORK(&virqfd->shutdown, virqfd_shutdown);
 126         INIT_WORK(&virqfd->inject, virqfd_inject);
 127
 128         irqfd = fdget(fd);
 129         if (!irqfd.file) {
 130                 ret = -EBADF;
 131                 goto err_fd;
 132         }
 133
 134         ctx = eventfd_ctx_fileget(irqfd.file);
 135         if (IS_ERR(ctx)) {
 136                 ret = PTR_ERR(ctx);
 137                 goto err_ctx;
 138         }
 139
 140         virqfd->eventfd = ctx;
 141
 142         /*
 143          * virqfds can be released by closing the eventfd or directly
 144          * through ioctl.  These are both done through a workqueue, so
 145          * we update the pointer to the virqfd under lock to avoid
 146          * pushing multiple jobs to release the same virqfd.
 147          */
 148         spin_lock_irq(&virqfd_lock);
 149
 150         if (*pvirqfd) {
 151                 spin_unlock_irq(&virqfd_lock);
 152                 ret = -EBUSY;
 153                 goto err_busy;
 154         }
 155         *pvirqfd = virqfd;
 156
 157         spin_unlock_irq(&virqfd_lock);
 158
 159         /*
 160          * Install our own custom wake-up handling so we are notified via
 161          * a callback whenever someone signals the underlying eventfd.
 162          */
 163         init_waitqueue_func_entry(&virqfd->wait, virqfd_wakeup);
 164         init_poll_funcptr(&virqfd->pt, virqfd_ptable_queue_proc);
 165
 166         events = vfs_poll(irqfd.file, &virqfd->pt);
 167
 168         /*
 169          * Check if there was an event already pending on the eventfd
 170          * before we registered and trigger it as if we didn't miss it.
 171          */
 172         if (events & EPOLLIN) {
 173                 if ((!handler || handler(opaque, data)) && thread)
 174                         schedule_work(&virqfd->inject);
 175         }
 176
 177         /*
 178          * Do not drop the file until the irqfd is fully initialized,
 179          * otherwise we might race against the EPOLLHUP.
 180          */
 181         fdput(irqfd);
 182
 183         return 0;
 184 err_busy:
 185         eventfd_ctx_put(ctx);
 186 err_ctx:
 187         fdput(irqfd);
 188 err_fd:
 189         kfree(virqfd);
 190
 191         return ret;
 192 }
 193 EXPORT_SYMBOL_GPL(vfio_virqfd_enable);
 194
 195 void vfio_virqfd_disable(struct virqfd **pvirqfd)
 196 {
 197         unsigned long flags;
 198
 199         spin_lock_irqsave(&virqfd_lock, flags);
 200
 201         if (*pvirqfd) {
 202                 virqfd_deactivate(*pvirqfd);
 203                 *pvirqfd = NULL;
 204         }
 205
 206         spin_unlock_irqrestore(&virqfd_lock, flags);
 207
 208         /*
 209          * Block until we know all outstanding shutdown jobs have completed.
 210          * Even if we don't queue the job, flush the wq to be sure it's
 211          * been released.
 212          */
 213         flush_workqueue(vfio_irqfd_cleanup_wq);
 214 }
 215 EXPORT_SYMBOL_GPL(vfio_virqfd_disable);
 216
 217 module_init(vfio_virqfd_init);
 218 module_exit(vfio_virqfd_exit);
 219
 220 MODULE_VERSION(DRIVER_VERSION);
 221 MODULE_LICENSE("GPL v2");
 222 MODULE_AUTHOR(DRIVER_AUTHOR);
 223 MODULE_DESCRIPTION(DRIVER_DESC);