linux/virt/kvm/eventfd.c
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   1/*
   2 * kvm eventfd support - use eventfd objects to signal various KVM events
   3 *
   4 * Copyright 2009 Novell.  All Rights Reserved.
   5 *
   6 * Author:
   7 *      Gregory Haskins <ghaskins@novell.com>
   8 *
   9 * This file is free software; you can redistribute it and/or modify
  10 * it under the terms of version 2 of the GNU General Public License
  11 * as published by the Free Software Foundation.
  12 *
  13 * This program is distributed in the hope that it will be useful,
  14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16 * GNU General Public License for more details.
  17 *
  18 * You should have received a copy of the GNU General Public License
  19 * along with this program; if not, write to the Free Software Foundation,
  20 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
  21 */
  22
  23#include <linux/kvm_host.h>
  24#include <linux/kvm.h>
  25#include <linux/workqueue.h>
  26#include <linux/syscalls.h>
  27#include <linux/wait.h>
  28#include <linux/poll.h>
  29#include <linux/file.h>
  30#include <linux/list.h>
  31#include <linux/eventfd.h>
  32#include <linux/kernel.h>
  33
  34#include "iodev.h"
  35
  36/*
  37 * --------------------------------------------------------------------
  38 * irqfd: Allows an fd to be used to inject an interrupt to the guest
  39 *
  40 * Credit goes to Avi Kivity for the original idea.
  41 * --------------------------------------------------------------------
  42 */
  43
  44struct _irqfd {
  45        struct kvm               *kvm;
  46        struct eventfd_ctx       *eventfd;
  47        int                       gsi;
  48        struct list_head          list;
  49        poll_table                pt;
  50        wait_queue_head_t        *wqh;
  51        wait_queue_t              wait;
  52        struct work_struct        inject;
  53        struct work_struct        shutdown;
  54};
  55
  56static struct workqueue_struct *irqfd_cleanup_wq;
  57
  58static void
  59irqfd_inject(struct work_struct *work)
  60{
  61        struct _irqfd *irqfd = container_of(work, struct _irqfd, inject);
  62        struct kvm *kvm = irqfd->kvm;
  63
  64        mutex_lock(&kvm->irq_lock);
  65        kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 1);
  66        kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 0);
  67        mutex_unlock(&kvm->irq_lock);
  68}
  69
  70/*
  71 * Race-free decouple logic (ordering is critical)
  72 */
  73static void
  74irqfd_shutdown(struct work_struct *work)
  75{
  76        struct _irqfd *irqfd = container_of(work, struct _irqfd, shutdown);
  77
  78        /*
  79         * Synchronize with the wait-queue and unhook ourselves to prevent
  80         * further events.
  81         */
  82        remove_wait_queue(irqfd->wqh, &irqfd->wait);
  83
  84        /*
  85         * We know no new events will be scheduled at this point, so block
  86         * until all previously outstanding events have completed
  87         */
  88        flush_work(&irqfd->inject);
  89
  90        /*
  91         * It is now safe to release the object's resources
  92         */
  93        eventfd_ctx_put(irqfd->eventfd);
  94        kfree(irqfd);
  95}
  96
  97
  98/* assumes kvm->irqfds.lock is held */
  99static bool
 100irqfd_is_active(struct _irqfd *irqfd)
 101{
 102        return list_empty(&irqfd->list) ? false : true;
 103}
 104
 105/*
 106 * Mark the irqfd as inactive and schedule it for removal
 107 *
 108 * assumes kvm->irqfds.lock is held
 109 */
 110static void
 111irqfd_deactivate(struct _irqfd *irqfd)
 112{
 113        BUG_ON(!irqfd_is_active(irqfd));
 114
 115        list_del_init(&irqfd->list);
 116
 117        queue_work(irqfd_cleanup_wq, &irqfd->shutdown);
 118}
 119
 120/*
 121 * Called with wqh->lock held and interrupts disabled
 122 */
 123static int
 124irqfd_wakeup(wait_queue_t *wait, unsigned mode, int sync, void *key)
 125{
 126        struct _irqfd *irqfd = container_of(wait, struct _irqfd, wait);
 127        unsigned long flags = (unsigned long)key;
 128
 129        if (flags & POLLIN)
 130                /* An event has been signaled, inject an interrupt */
 131                schedule_work(&irqfd->inject);
 132
 133        if (flags & POLLHUP) {
 134                /* The eventfd is closing, detach from KVM */
 135                struct kvm *kvm = irqfd->kvm;
 136                unsigned long flags;
 137
 138                spin_lock_irqsave(&kvm->irqfds.lock, flags);
 139
 140                /*
 141                 * We must check if someone deactivated the irqfd before
 142                 * we could acquire the irqfds.lock since the item is
 143                 * deactivated from the KVM side before it is unhooked from
 144                 * the wait-queue.  If it is already deactivated, we can
 145                 * simply return knowing the other side will cleanup for us.
 146                 * We cannot race against the irqfd going away since the
 147                 * other side is required to acquire wqh->lock, which we hold
 148                 */
 149                if (irqfd_is_active(irqfd))
 150                        irqfd_deactivate(irqfd);
 151
 152                spin_unlock_irqrestore(&kvm->irqfds.lock, flags);
 153        }
 154
 155        return 0;
 156}
 157
 158static void
 159irqfd_ptable_queue_proc(struct file *file, wait_queue_head_t *wqh,
 160                        poll_table *pt)
 161{
 162        struct _irqfd *irqfd = container_of(pt, struct _irqfd, pt);
 163
 164        irqfd->wqh = wqh;
 165        add_wait_queue(wqh, &irqfd->wait);
 166}
 167
 168static int
 169kvm_irqfd_assign(struct kvm *kvm, int fd, int gsi)
 170{
 171        struct _irqfd *irqfd;
 172        struct file *file = NULL;
 173        struct eventfd_ctx *eventfd = NULL;
 174        int ret;
 175        unsigned int events;
 176
 177        irqfd = kzalloc(sizeof(*irqfd), GFP_KERNEL);
 178        if (!irqfd)
 179                return -ENOMEM;
 180
 181        irqfd->kvm = kvm;
 182        irqfd->gsi = gsi;
 183        INIT_LIST_HEAD(&irqfd->list);
 184        INIT_WORK(&irqfd->inject, irqfd_inject);
 185        INIT_WORK(&irqfd->shutdown, irqfd_shutdown);
 186
 187        file = eventfd_fget(fd);
 188        if (IS_ERR(file)) {
 189                ret = PTR_ERR(file);
 190                goto fail;
 191        }
 192
 193        eventfd = eventfd_ctx_fileget(file);
 194        if (IS_ERR(eventfd)) {
 195                ret = PTR_ERR(eventfd);
 196                goto fail;
 197        }
 198
 199        irqfd->eventfd = eventfd;
 200
 201        /*
 202         * Install our own custom wake-up handling so we are notified via
 203         * a callback whenever someone signals the underlying eventfd
 204         */
 205        init_waitqueue_func_entry(&irqfd->wait, irqfd_wakeup);
 206        init_poll_funcptr(&irqfd->pt, irqfd_ptable_queue_proc);
 207
 208        events = file->f_op->poll(file, &irqfd->pt);
 209
 210        spin_lock_irq(&kvm->irqfds.lock);
 211        list_add_tail(&irqfd->list, &kvm->irqfds.items);
 212        spin_unlock_irq(&kvm->irqfds.lock);
 213
 214        /*
 215         * Check if there was an event already pending on the eventfd
 216         * before we registered, and trigger it as if we didn't miss it.
 217         */
 218        if (events & POLLIN)
 219                schedule_work(&irqfd->inject);
 220
 221        /*
 222         * do not drop the file until the irqfd is fully initialized, otherwise
 223         * we might race against the POLLHUP
 224         */
 225        fput(file);
 226
 227        return 0;
 228
 229fail:
 230        if (eventfd && !IS_ERR(eventfd))
 231                eventfd_ctx_put(eventfd);
 232
 233        if (!IS_ERR(file))
 234                fput(file);
 235
 236        kfree(irqfd);
 237        return ret;
 238}
 239
 240void
 241kvm_eventfd_init(struct kvm *kvm)
 242{
 243        spin_lock_init(&kvm->irqfds.lock);
 244        INIT_LIST_HEAD(&kvm->irqfds.items);
 245        INIT_LIST_HEAD(&kvm->ioeventfds);
 246}
 247
 248/*
 249 * shutdown any irqfd's that match fd+gsi
 250 */
 251static int
 252kvm_irqfd_deassign(struct kvm *kvm, int fd, int gsi)
 253{
 254        struct _irqfd *irqfd, *tmp;
 255        struct eventfd_ctx *eventfd;
 256
 257        eventfd = eventfd_ctx_fdget(fd);
 258        if (IS_ERR(eventfd))
 259                return PTR_ERR(eventfd);
 260
 261        spin_lock_irq(&kvm->irqfds.lock);
 262
 263        list_for_each_entry_safe(irqfd, tmp, &kvm->irqfds.items, list) {
 264                if (irqfd->eventfd == eventfd && irqfd->gsi == gsi)
 265                        irqfd_deactivate(irqfd);
 266        }
 267
 268        spin_unlock_irq(&kvm->irqfds.lock);
 269        eventfd_ctx_put(eventfd);
 270
 271        /*
 272         * Block until we know all outstanding shutdown jobs have completed
 273         * so that we guarantee there will not be any more interrupts on this
 274         * gsi once this deassign function returns.
 275         */
 276        flush_workqueue(irqfd_cleanup_wq);
 277
 278        return 0;
 279}
 280
 281int
 282kvm_irqfd(struct kvm *kvm, int fd, int gsi, int flags)
 283{
 284        if (flags & KVM_IRQFD_FLAG_DEASSIGN)
 285                return kvm_irqfd_deassign(kvm, fd, gsi);
 286
 287        return kvm_irqfd_assign(kvm, fd, gsi);
 288}
 289
 290/*
 291 * This function is called as the kvm VM fd is being released. Shutdown all
 292 * irqfds that still remain open
 293 */
 294void
 295kvm_irqfd_release(struct kvm *kvm)
 296{
 297        struct _irqfd *irqfd, *tmp;
 298
 299        spin_lock_irq(&kvm->irqfds.lock);
 300
 301        list_for_each_entry_safe(irqfd, tmp, &kvm->irqfds.items, list)
 302                irqfd_deactivate(irqfd);
 303
 304        spin_unlock_irq(&kvm->irqfds.lock);
 305
 306        /*
 307         * Block until we know all outstanding shutdown jobs have completed
 308         * since we do not take a kvm* reference.
 309         */
 310        flush_workqueue(irqfd_cleanup_wq);
 311
 312}
 313
 314/*
 315 * create a host-wide workqueue for issuing deferred shutdown requests
 316 * aggregated from all vm* instances. We need our own isolated single-thread
 317 * queue to prevent deadlock against flushing the normal work-queue.
 318 */
 319static int __init irqfd_module_init(void)
 320{
 321        irqfd_cleanup_wq = create_singlethread_workqueue("kvm-irqfd-cleanup");
 322        if (!irqfd_cleanup_wq)
 323                return -ENOMEM;
 324
 325        return 0;
 326}
 327
 328static void __exit irqfd_module_exit(void)
 329{
 330        destroy_workqueue(irqfd_cleanup_wq);
 331}
 332
 333module_init(irqfd_module_init);
 334module_exit(irqfd_module_exit);
 335
 336/*
 337 * --------------------------------------------------------------------
 338 * ioeventfd: translate a PIO/MMIO memory write to an eventfd signal.
 339 *
 340 * userspace can register a PIO/MMIO address with an eventfd for receiving
 341 * notification when the memory has been touched.
 342 * --------------------------------------------------------------------
 343 */
 344
 345struct _ioeventfd {
 346        struct list_head     list;
 347        u64                  addr;
 348        int                  length;
 349        struct eventfd_ctx  *eventfd;
 350        u64                  datamatch;
 351        struct kvm_io_device dev;
 352        bool                 wildcard;
 353};
 354
 355static inline struct _ioeventfd *
 356to_ioeventfd(struct kvm_io_device *dev)
 357{
 358        return container_of(dev, struct _ioeventfd, dev);
 359}
 360
 361static void
 362ioeventfd_release(struct _ioeventfd *p)
 363{
 364        eventfd_ctx_put(p->eventfd);
 365        list_del(&p->list);
 366        kfree(p);
 367}
 368
 369static bool
 370ioeventfd_in_range(struct _ioeventfd *p, gpa_t addr, int len, const void *val)
 371{
 372        u64 _val;
 373
 374        if (!(addr == p->addr && len == p->length))
 375                /* address-range must be precise for a hit */
 376                return false;
 377
 378        if (p->wildcard)
 379                /* all else equal, wildcard is always a hit */
 380                return true;
 381
 382        /* otherwise, we have to actually compare the data */
 383
 384        BUG_ON(!IS_ALIGNED((unsigned long)val, len));
 385
 386        switch (len) {
 387        case 1:
 388                _val = *(u8 *)val;
 389                break;
 390        case 2:
 391                _val = *(u16 *)val;
 392                break;
 393        case 4:
 394                _val = *(u32 *)val;
 395                break;
 396        case 8:
 397                _val = *(u64 *)val;
 398                break;
 399        default:
 400                return false;
 401        }
 402
 403        return _val == p->datamatch ? true : false;
 404}
 405
 406/* MMIO/PIO writes trigger an event if the addr/val match */
 407static int
 408ioeventfd_write(struct kvm_io_device *this, gpa_t addr, int len,
 409                const void *val)
 410{
 411        struct _ioeventfd *p = to_ioeventfd(this);
 412
 413        if (!ioeventfd_in_range(p, addr, len, val))
 414                return -EOPNOTSUPP;
 415
 416        eventfd_signal(p->eventfd, 1);
 417        return 0;
 418}
 419
 420/*
 421 * This function is called as KVM is completely shutting down.  We do not
 422 * need to worry about locking just nuke anything we have as quickly as possible
 423 */
 424static void
 425ioeventfd_destructor(struct kvm_io_device *this)
 426{
 427        struct _ioeventfd *p = to_ioeventfd(this);
 428
 429        ioeventfd_release(p);
 430}
 431
 432static const struct kvm_io_device_ops ioeventfd_ops = {
 433        .write      = ioeventfd_write,
 434        .destructor = ioeventfd_destructor,
 435};
 436
 437/* assumes kvm->slots_lock held */
 438static bool
 439ioeventfd_check_collision(struct kvm *kvm, struct _ioeventfd *p)
 440{
 441        struct _ioeventfd *_p;
 442
 443        list_for_each_entry(_p, &kvm->ioeventfds, list)
 444                if (_p->addr == p->addr && _p->length == p->length &&
 445                    (_p->wildcard || p->wildcard ||
 446                     _p->datamatch == p->datamatch))
 447                        return true;
 448
 449        return false;
 450}
 451
 452static int
 453kvm_assign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
 454{
 455        int                       pio = args->flags & KVM_IOEVENTFD_FLAG_PIO;
 456        struct kvm_io_bus        *bus = pio ? &kvm->pio_bus : &kvm->mmio_bus;
 457        struct _ioeventfd        *p;
 458        struct eventfd_ctx       *eventfd;
 459        int                       ret;
 460
 461        /* must be natural-word sized */
 462        switch (args->len) {
 463        case 1:
 464        case 2:
 465        case 4:
 466        case 8:
 467                break;
 468        default:
 469                return -EINVAL;
 470        }
 471
 472        /* check for range overflow */
 473        if (args->addr + args->len < args->addr)
 474                return -EINVAL;
 475
 476        /* check for extra flags that we don't understand */
 477        if (args->flags & ~KVM_IOEVENTFD_VALID_FLAG_MASK)
 478                return -EINVAL;
 479
 480        eventfd = eventfd_ctx_fdget(args->fd);
 481        if (IS_ERR(eventfd))
 482                return PTR_ERR(eventfd);
 483
 484        p = kzalloc(sizeof(*p), GFP_KERNEL);
 485        if (!p) {
 486                ret = -ENOMEM;
 487                goto fail;
 488        }
 489
 490        INIT_LIST_HEAD(&p->list);
 491        p->addr    = args->addr;
 492        p->length  = args->len;
 493        p->eventfd = eventfd;
 494
 495        /* The datamatch feature is optional, otherwise this is a wildcard */
 496        if (args->flags & KVM_IOEVENTFD_FLAG_DATAMATCH)
 497                p->datamatch = args->datamatch;
 498        else
 499                p->wildcard = true;
 500
 501        down_write(&kvm->slots_lock);
 502
 503        /* Verify that there isnt a match already */
 504        if (ioeventfd_check_collision(kvm, p)) {
 505                ret = -EEXIST;
 506                goto unlock_fail;
 507        }
 508
 509        kvm_iodevice_init(&p->dev, &ioeventfd_ops);
 510
 511        ret = __kvm_io_bus_register_dev(bus, &p->dev);
 512        if (ret < 0)
 513                goto unlock_fail;
 514
 515        list_add_tail(&p->list, &kvm->ioeventfds);
 516
 517        up_write(&kvm->slots_lock);
 518
 519        return 0;
 520
 521unlock_fail:
 522        up_write(&kvm->slots_lock);
 523
 524fail:
 525        kfree(p);
 526        eventfd_ctx_put(eventfd);
 527
 528        return ret;
 529}
 530
 531static int
 532kvm_deassign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
 533{
 534        int                       pio = args->flags & KVM_IOEVENTFD_FLAG_PIO;
 535        struct kvm_io_bus        *bus = pio ? &kvm->pio_bus : &kvm->mmio_bus;
 536        struct _ioeventfd        *p, *tmp;
 537        struct eventfd_ctx       *eventfd;
 538        int                       ret = -ENOENT;
 539
 540        eventfd = eventfd_ctx_fdget(args->fd);
 541        if (IS_ERR(eventfd))
 542                return PTR_ERR(eventfd);
 543
 544        down_write(&kvm->slots_lock);
 545
 546        list_for_each_entry_safe(p, tmp, &kvm->ioeventfds, list) {
 547                bool wildcard = !(args->flags & KVM_IOEVENTFD_FLAG_DATAMATCH);
 548
 549                if (p->eventfd != eventfd  ||
 550                    p->addr != args->addr  ||
 551                    p->length != args->len ||
 552                    p->wildcard != wildcard)
 553                        continue;
 554
 555                if (!p->wildcard && p->datamatch != args->datamatch)
 556                        continue;
 557
 558                __kvm_io_bus_unregister_dev(bus, &p->dev);
 559                ioeventfd_release(p);
 560                ret = 0;
 561                break;
 562        }
 563
 564        up_write(&kvm->slots_lock);
 565
 566        eventfd_ctx_put(eventfd);
 567
 568        return ret;
 569}
 570
 571int
 572kvm_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
 573{
 574        if (args->flags & KVM_IOEVENTFD_FLAG_DEASSIGN)
 575                return kvm_deassign_ioeventfd(kvm, args);
 576
 577        return kvm_assign_ioeventfd(kvm, args);
 578}
 579