/* Copyright (C) 2009 Red Hat, Inc. * Copyright (C) 2006 Rusty Russell IBM Corporation * * Author: Michael S. Tsirkin * * Inspiration, some code, and most witty comments come from * Documentation/virtual/lguest/lguest.c, by Rusty Russell * * This work is licensed under the terms of the GNU GPL, version 2. * * Generic code for virtio server in host kernel. */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include "vhost.h" static ushort max_mem_regions = 64; module_param(max_mem_regions, ushort, 0444); MODULE_PARM_DESC(max_mem_regions, "Maximum number of memory regions in memory map. (default: 64)"); enum { VHOST_MEMORY_F_LOG = 0x1, }; #define vhost_used_event(vq) ((__virtio16 __user *)&vq->avail->ring[vq->num]) #define vhost_avail_event(vq) ((__virtio16 __user *)&vq->used->ring[vq->num]) #ifdef CONFIG_VHOST_CROSS_ENDIAN_LEGACY static void vhost_disable_cross_endian(struct vhost_virtqueue *vq) { vq->user_be = !virtio_legacy_is_little_endian(); } static void vhost_enable_cross_endian_big(struct vhost_virtqueue *vq) { vq->user_be = true; } static void vhost_enable_cross_endian_little(struct vhost_virtqueue *vq) { vq->user_be = false; } static long vhost_set_vring_endian(struct vhost_virtqueue *vq, int __user *argp) { struct vhost_vring_state s; if (vq->private_data) return -EBUSY; if (copy_from_user(&s, argp, sizeof(s))) return -EFAULT; if (s.num != VHOST_VRING_LITTLE_ENDIAN && s.num != VHOST_VRING_BIG_ENDIAN) return -EINVAL; if (s.num == VHOST_VRING_BIG_ENDIAN) vhost_enable_cross_endian_big(vq); else vhost_enable_cross_endian_little(vq); return 0; } static long vhost_get_vring_endian(struct vhost_virtqueue *vq, u32 idx, int __user *argp) { struct vhost_vring_state s = { .index = idx, .num = vq->user_be }; if (copy_to_user(argp, &s, sizeof(s))) return -EFAULT; return 0; } static void vhost_init_is_le(struct vhost_virtqueue *vq) { /* Note for legacy virtio: user_be is initialized at reset time * according to the host endianness. If userspace does not set an * explicit endianness, the default behavior is native endian, as * expected by legacy virtio. */ vq->is_le = vhost_has_feature(vq, VIRTIO_F_VERSION_1) || !vq->user_be; } #else static void vhost_disable_cross_endian(struct vhost_virtqueue *vq) { } static long vhost_set_vring_endian(struct vhost_virtqueue *vq, int __user *argp) { return -ENOIOCTLCMD; } static long vhost_get_vring_endian(struct vhost_virtqueue *vq, u32 idx, int __user *argp) { return -ENOIOCTLCMD; } static void vhost_init_is_le(struct vhost_virtqueue *vq) { if (vhost_has_feature(vq, VIRTIO_F_VERSION_1)) vq->is_le = true; } #endif /* CONFIG_VHOST_CROSS_ENDIAN_LEGACY */ static void vhost_reset_is_le(struct vhost_virtqueue *vq) { vq->is_le = virtio_legacy_is_little_endian(); } static void vhost_poll_func(struct file *file, wait_queue_head_t *wqh, poll_table *pt) { struct vhost_poll *poll; poll = container_of(pt, struct vhost_poll, table); poll->wqh = wqh; add_wait_queue(wqh, &poll->wait); } static int vhost_poll_wakeup(wait_queue_t *wait, unsigned mode, int sync, void *key) { struct vhost_poll *poll = container_of(wait, struct vhost_poll, wait); if (!((unsigned long)key & poll->mask)) return 0; vhost_poll_queue(poll); return 0; } void vhost_work_init(struct vhost_work *work, vhost_work_fn_t fn) { INIT_LIST_HEAD(&work->node); work->fn = fn; init_waitqueue_head(&work->done); work->flushing = 0; work->queue_seq = work->done_seq = 0; } EXPORT_SYMBOL_GPL(vhost_work_init); /* Init poll structure */ void vhost_poll_init(struct vhost_poll *poll, vhost_work_fn_t fn, unsigned long mask, struct vhost_dev *dev) { init_waitqueue_func_entry(&poll->wait, vhost_poll_wakeup); init_poll_funcptr(&poll->table, vhost_poll_func); poll->mask = mask; poll->dev = dev; poll->wqh = NULL; vhost_work_init(&poll->work, fn); } EXPORT_SYMBOL_GPL(vhost_poll_init); /* Start polling a file. We add ourselves to file's wait queue. The caller must * keep a reference to a file until after vhost_poll_stop is called. */ int vhost_poll_start(struct vhost_poll *poll, struct file *file) { unsigned long mask; int ret = 0; if (poll->wqh) return 0; mask = file->f_op->poll(file, &poll->table); if (mask) vhost_poll_wakeup(&poll->wait, 0, 0, (void *)mask); if (mask & POLLERR) { if (poll->wqh) remove_wait_queue(poll->wqh, &poll->wait); ret = -EINVAL; } return ret; } EXPORT_SYMBOL_GPL(vhost_poll_start); /* Stop polling a file. After this function returns, it becomes safe to drop the * file reference. You must also flush afterwards. */ void vhost_poll_stop(struct vhost_poll *poll) { if (poll->wqh) { remove_wait_queue(poll->wqh, &poll->wait); poll->wqh = NULL; } } EXPORT_SYMBOL_GPL(vhost_poll_stop); static bool vhost_work_seq_done(struct vhost_dev *dev, struct vhost_work *work, unsigned seq) { int left; spin_lock_irq(&dev->work_lock); left = seq - work->done_seq; spin_unlock_irq(&dev->work_lock); return left <= 0; } void vhost_work_flush(struct vhost_dev *dev, struct vhost_work *work) { unsigned seq; int flushing; spin_lock_irq(&dev->work_lock); seq = work->queue_seq; work->flushing++; spin_unlock_irq(&dev->work_lock); wait_event(work->done, vhost_work_seq_done(dev, work, seq)); spin_lock_irq(&dev->work_lock); flushing = --work->flushing; spin_unlock_irq(&dev->work_lock); BUG_ON(flushing < 0); } EXPORT_SYMBOL_GPL(vhost_work_flush); /* Flush any work that has been scheduled. When calling this, don't hold any * locks that are also used by the callback. */ void vhost_poll_flush(struct vhost_poll *poll) { vhost_work_flush(poll->dev, &poll->work); } EXPORT_SYMBOL_GPL(vhost_poll_flush); void vhost_work_queue(struct vhost_dev *dev, struct vhost_work *work) { unsigned long flags; spin_lock_irqsave(&dev->work_lock, flags); if (list_empty(&work->node)) { list_add_tail(&work->node, &dev->work_list); work->queue_seq++; spin_unlock_irqrestore(&dev->work_lock, flags); wake_up_process(dev->worker); } else { spin_unlock_irqrestore(&dev->work_lock, flags); } } EXPORT_SYMBOL_GPL(vhost_work_queue); /* A lockless hint for busy polling code to exit the loop */ bool vhost_has_work(struct vhost_dev *dev) { return !list_empty(&dev->work_list); } EXPORT_SYMBOL_GPL(vhost_has_work); void vhost_poll_queue(struct vhost_poll *poll) { vhost_work_queue(poll->dev, &poll->work); } EXPORT_SYMBOL_GPL(vhost_poll_queue); static void vhost_vq_reset(struct vhost_dev *dev, struct vhost_virtqueue *vq) { vq->num = 1; vq->desc = NULL; vq->avail = NULL; vq->used = NULL; vq->last_avail_idx = 0; vq->avail_idx = 0; vq->last_used_idx = 0; vq->signalled_used = 0; vq->signalled_used_valid = false; vq->used_flags = 0; vq->log_used = false; vq->log_addr = -1ull; vq->private_data = NULL; vq->acked_features = 0; vq->log_base = NULL; vq->error_ctx = NULL; vq->error = NULL; vq->kick = NULL; vq->call_ctx = NULL; vq->call = NULL; vq->log_ctx = NULL; vq->memory = NULL; vhost_reset_is_le(vq); vhost_disable_cross_endian(vq); } static int vhost_worker(void *data) { struct vhost_dev *dev = data; struct vhost_work *work = NULL; unsigned uninitialized_var(seq); mm_segment_t oldfs = get_fs(); set_fs(USER_DS); use_mm(dev->mm); for (;;) { /* mb paired w/ kthread_stop */ set_current_state(TASK_INTERRUPTIBLE); spin_lock_irq(&dev->work_lock); if (work) { work->done_seq = seq; if (work->flushing) wake_up_all(&work->done); } if (kthread_should_stop()) { spin_unlock_irq(&dev->work_lock); __set_current_state(TASK_RUNNING); break; } if (!list_empty(&dev->work_list)) { work = list_first_entry(&dev->work_list, struct vhost_work, node); list_del_init(&work->node); seq = work->queue_seq; } else work = NULL; spin_unlock_irq(&dev->work_lock); if (work) { __set_current_state(TASK_RUNNING); work->fn(work); if (need_resched()) schedule(); } else schedule(); } unuse_mm(dev->mm); set_fs(oldfs); return 0; } static void vhost_vq_free_iovecs(struct vhost_virtqueue *vq) { kfree(vq->indirect); vq->indirect = NULL; kfree(vq->log); vq->log = NULL; kfree(vq->heads); vq->heads = NULL; } /* Helper to allocate iovec buffers for all vqs. */ static long vhost_dev_alloc_iovecs(struct vhost_dev *dev) { struct vhost_virtqueue *vq; int i; for (i = 0; i < dev->nvqs; ++i) { vq = dev->vqs[i]; vq->indirect = kmalloc(sizeof *vq->indirect * UIO_MAXIOV, GFP_KERNEL); vq->log = kmalloc(sizeof *vq->log * UIO_MAXIOV, GFP_KERNEL); vq->heads = kmalloc(sizeof *vq->heads * UIO_MAXIOV, GFP_KERNEL); if (!vq->indirect || !vq->log || !vq->heads) goto err_nomem; } return 0; err_nomem: for (; i >= 0; --i) vhost_vq_free_iovecs(dev->vqs[i]); return -ENOMEM; } static void vhost_dev_free_iovecs(struct vhost_dev *dev) { int i; for (i = 0; i < dev->nvqs; ++i) vhost_vq_free_iovecs(dev->vqs[i]); } void vhost_dev_init(struct vhost_dev *dev, struct vhost_virtqueue **vqs, int nvqs) { struct vhost_virtqueue *vq; int i; dev->vqs = vqs; dev->nvqs = nvqs; mutex_init(&dev->mutex); dev->log_ctx = NULL; dev->log_file = NULL; dev->memory = NULL; dev->mm = NULL; spin_lock_init(&dev->work_lock); INIT_LIST_HEAD(&dev->work_list); dev->worker = NULL; for (i = 0; i < dev->nvqs; ++i) { vq = dev->vqs[i]; vq->log = NULL; vq->indirect = NULL; vq->heads = NULL; vq->dev = dev; mutex_init(&vq->mutex); vhost_vq_reset(dev, vq); if (vq->handle_kick) vhost_poll_init(&vq->poll, vq->handle_kick, POLLIN, dev); } } EXPORT_SYMBOL_GPL(vhost_dev_init); /* Caller should have device mutex */ long vhost_dev_check_owner(struct vhost_dev *dev) { /* Are you the owner? If not, I don't think you mean to do that */ return dev->mm == current->mm ? 0 : -EPERM; } EXPORT_SYMBOL_GPL(vhost_dev_check_owner); struct vhost_attach_cgroups_struct { struct vhost_work work; struct task_struct *owner; int ret; }; static void vhost_attach_cgroups_work(struct vhost_work *work) { struct vhost_attach_cgroups_struct *s; s = container_of(work, struct vhost_attach_cgroups_struct, work); s->ret = cgroup_attach_task_all(s->owner, current); } static int vhost_attach_cgroups(struct vhost_dev *dev) { struct vhost_attach_cgroups_struct attach; attach.owner = current; vhost_work_init(&attach.work, vhost_attach_cgroups_work); vhost_work_queue(dev, &attach.work); vhost_work_flush(dev, &attach.work); return attach.ret; } /* Caller should have device mutex */ bool vhost_dev_has_owner(struct vhost_dev *dev) { return dev->mm; } EXPORT_SYMBOL_GPL(vhost_dev_has_owner); /* Caller should have device mutex */ long vhost_dev_set_owner(struct vhost_dev *dev) { struct task_struct *worker; int err; /* Is there an owner already? */ if (vhost_dev_has_owner(dev)) { err = -EBUSY; goto err_mm; } /* No owner, become one */ dev->mm = get_task_mm(current); worker = kthread_create(vhost_worker, dev, "vhost-%d", current->pid); if (IS_ERR(worker)) { err = PTR_ERR(worker); goto err_worker; } dev->worker = worker; wake_up_process(worker); /* avoid contributing to loadavg */ err = vhost_attach_cgroups(dev); if (err) goto err_cgroup; err = vhost_dev_alloc_iovecs(dev); if (err) goto err_cgroup; return 0; err_cgroup: kthread_stop(worker); dev->worker = NULL; err_worker: if (dev->mm) mmput(dev->mm); dev->mm = NULL; err_mm: return err; } EXPORT_SYMBOL_GPL(vhost_dev_set_owner); struct vhost_memory *vhost_dev_reset_owner_prepare(void) { return kmalloc(offsetof(struct vhost_memory, regions), GFP_KERNEL); } EXPORT_SYMBOL_GPL(vhost_dev_reset_owner_prepare); /* Caller should have device mutex */ void vhost_dev_reset_owner(struct vhost_dev *dev, struct vhost_memory *memory) { int i; vhost_dev_cleanup(dev, true); /* Restore memory to default empty mapping. */ memory->nregions = 0; dev->memory = memory; /* We don't need VQ locks below since vhost_dev_cleanup makes sure * VQs aren't running. */ for (i = 0; i < dev->nvqs; ++i) dev->vqs[i]->memory = memory; } EXPORT_SYMBOL_GPL(vhost_dev_reset_owner); void vhost_dev_stop(struct vhost_dev *dev) { int i; for (i = 0; i < dev->nvqs; ++i) { if (dev->vqs[i]->kick && dev->vqs[i]->handle_kick) { vhost_poll_stop(&dev->vqs[i]->poll); vhost_poll_flush(&dev->vqs[i]->poll); } } } EXPORT_SYMBOL_GPL(vhost_dev_stop); /* Caller should have device mutex if and only if locked is set */ void vhost_dev_cleanup(struct vhost_dev *dev, bool locked) { int i; for (i = 0; i < dev->nvqs; ++i) { if (dev->vqs[i]->error_ctx) eventfd_ctx_put(dev->vqs[i]->error_ctx); if (dev->vqs[i]->error) fput(dev->vqs[i]->error); if (dev->vqs[i]->kick) fput(dev->vqs[i]->kick); if (dev->vqs[i]->call_ctx) eventfd_ctx_put(dev->vqs[i]->call_ctx); if (dev->vqs[i]->call) fput(dev->vqs[i]->call); vhost_vq_reset(dev, dev->vqs[i]); } vhost_dev_free_iovecs(dev); if (dev->log_ctx) eventfd_ctx_put(dev->log_ctx); dev->log_ctx = NULL; if (dev->log_file) fput(dev->log_file); dev->log_file = NULL; /* No one will access memory at this point */ kvfree(dev->memory); dev->memory = NULL; WARN_ON(!list_empty(&dev->work_list)); if (dev->worker) { kthread_stop(dev->worker); dev->worker = NULL; } if (dev->mm) mmput(dev->mm); dev->mm = NULL; } EXPORT_SYMBOL_GPL(vhost_dev_cleanup); static int log_access_ok(void __user *log_base, u64 addr, unsigned long sz) { u64 a = addr / VHOST_PAGE_SIZE / 8; /* Make sure 64 bit math will not overflow. */ if (a > ULONG_MAX - (unsigned long)log_base || a + (unsigned long)log_base > ULONG_MAX) return 0; return access_ok(VERIFY_WRITE, log_base + a, (sz + VHOST_PAGE_SIZE * 8 - 1) / VHOST_PAGE_SIZE / 8); } /* Caller should have vq mutex and device mutex. */ static int vq_memory_access_ok(void __user *log_base, struct vhost_memory *mem, int log_all) { int i; if (!mem) return 0; for (i = 0; i < mem->nregions; ++i) { struct vhost_memory_region *m = mem->regions + i; unsigned long a = m->userspace_addr; if (m->memory_size > ULONG_MAX) return 0; else if (!access_ok(VERIFY_WRITE, (void __user *)a, m->memory_size)) return 0; else if (log_all && !log_access_ok(log_base, m->guest_phys_addr, m->memory_size)) return 0; } return 1; } /* Can we switch to this memory table? */ /* Caller should have device mutex but not vq mutex */ static int memory_access_ok(struct vhost_dev *d, struct vhost_memory *mem, int log_all) { int i; for (i = 0; i < d->nvqs; ++i) { int ok; bool log; mutex_lock(&d->vqs[i]->mutex); log = log_all || vhost_has_feature(d->vqs[i], VHOST_F_LOG_ALL); /* If ring is inactive, will check when it's enabled. */ if (d->vqs[i]->private_data) ok = vq_memory_access_ok(d->vqs[i]->log_base, mem, log); else ok = 1; mutex_unlock(&d->vqs[i]->mutex); if (!ok) return 0; } return 1; } static int vq_access_ok(struct vhost_virtqueue *vq, unsigned int num, struct vring_desc __user *desc, struct vring_avail __user *avail, struct vring_used __user *used) { size_t s = vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX) ? 2 : 0; return access_ok(VERIFY_READ, desc, num * sizeof *desc) && access_ok(VERIFY_READ, avail, sizeof *avail + num * sizeof *avail->ring + s) && access_ok(VERIFY_WRITE, used, sizeof *used + num * sizeof *used->ring + s); } /* Can we log writes? */ /* Caller should have device mutex but not vq mutex */ int vhost_log_access_ok(struct vhost_dev *dev) { return memory_access_ok(dev, dev->memory, 1); } EXPORT_SYMBOL_GPL(vhost_log_access_ok); /* Verify access for write logging. */ /* Caller should have vq mutex and device mutex */ static int vq_log_access_ok(struct vhost_virtqueue *vq, void __user *log_base) { size_t s = vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX) ? 2 : 0; return vq_memory_access_ok(log_base, vq->memory, vhost_has_feature(vq, VHOST_F_LOG_ALL)) && (!vq->log_used || log_access_ok(log_base, vq->log_addr, sizeof *vq->used + vq->num * sizeof *vq->used->ring + s)); } /* Can we start vq? */ /* Caller should have vq mutex and device mutex */ int vhost_vq_access_ok(struct vhost_virtqueue *vq) { return vq_access_ok(vq, vq->num, vq->desc, vq->avail, vq->used) && vq_log_access_ok(vq, vq->log_base); } EXPORT_SYMBOL_GPL(vhost_vq_access_ok); static int vhost_memory_reg_sort_cmp(const void *p1, const void *p2) { const struct vhost_memory_region *r1 = p1, *r2 = p2; if (r1->guest_phys_addr < r2->guest_phys_addr) return 1; if (r1->guest_phys_addr > r2->guest_phys_addr) return -1; return 0; } static void *vhost_kvzalloc(unsigned long size) { void *n = kzalloc(size, GFP_KERNEL | __GFP_NOWARN | __GFP_REPEAT); if (!n) n = vzalloc(size); return n; } static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m) { struct vhost_memory mem, *newmem, *oldmem; unsigned long size = offsetof(struct vhost_memory, regions); int i; if (copy_from_user(&mem, m, size)) return -EFAULT; if (mem.padding) return -EOPNOTSUPP; if (mem.nregions > max_mem_regions) return -E2BIG; newmem = vhost_kvzalloc(size + mem.nregions * sizeof(*m->regions)); if (!newmem) return -ENOMEM; memcpy(newmem, &mem, size); if (copy_from_user(newmem->regions, m->regions, mem.nregions * sizeof *m->regions)) { kvfree(newmem); return -EFAULT; } sort(newmem->regions, newmem->nregions, sizeof(*newmem->regions), vhost_memory_reg_sort_cmp, NULL); if (!memory_access_ok(d, newmem, 0)) { kvfree(newmem); return -EFAULT; } oldmem = d->memory; d->memory = newmem; /* All memory accesses are done under some VQ mutex. */ for (i = 0; i < d->nvqs; ++i) { mutex_lock(&d->vqs[i]->mutex); d->vqs[i]->memory = newmem; mutex_unlock(&d->vqs[i]->mutex); } kvfree(oldmem); return 0; } long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp) { struct file *eventfp, *filep = NULL; bool pollstart = false, pollstop = false; struct eventfd_ctx *ctx = NULL; u32 __user *idxp = argp; struct vhost_virtqueue *vq; struct vhost_vring_state s; struct vhost_vring_file f; struct vhost_vring_addr a; u32 idx; long r; r = get_user(idx, idxp); if (r < 0) return r; if (idx >= d->nvqs) return -ENOBUFS; vq = d->vqs[idx]; mutex_lock(&vq->mutex); switch (ioctl) { case VHOST_SET_VRING_NUM: /* Resizing ring with an active backend? * You don't want to do that. */ if (vq->private_data) { r = -EBUSY; break; } if (copy_from_user(&s, argp, sizeof s)) { r = -EFAULT; break; } if (!s.num || s.num > 0xffff || (s.num & (s.num - 1))) { r = -EINVAL; break; } vq->num = s.num; break; case VHOST_SET_VRING_BASE: /* Moving base with an active backend? * You don't want to do that. */ if (vq->private_data) { r = -EBUSY; break; } if (copy_from_user(&s, argp, sizeof s)) { r = -EFAULT; break; } if (s.num > 0xffff) { r = -EINVAL; break; } vq->last_avail_idx = s.num; /* Forget the cached index value. */ vq->avail_idx = vq->last_avail_idx; break; case VHOST_GET_VRING_BASE: s.index = idx; s.num = vq->last_avail_idx; if (copy_to_user(argp, &s, sizeof s)) r = -EFAULT; break; case VHOST_SET_VRING_ADDR: if (copy_from_user(&a, argp, sizeof a)) { r = -EFAULT; break; } if (a.flags & ~(0x1 << VHOST_VRING_F_LOG)) { r = -EOPNOTSUPP; break; } /* For 32bit, verify that the top 32bits of the user data are set to zero. */ if ((u64)(unsigned long)a.desc_user_addr != a.desc_user_addr || (u64)(unsigned long)a.used_user_addr != a.used_user_addr || (u64)(unsigned long)a.avail_user_addr != a.avail_user_addr) { r = -EFAULT; break; } /* Make sure it's safe to cast pointers to vring types. */ BUILD_BUG_ON(__alignof__ *vq->avail > VRING_AVAIL_ALIGN_SIZE); BUILD_BUG_ON(__alignof__ *vq->used > VRING_USED_ALIGN_SIZE); if ((a.avail_user_addr & (VRING_AVAIL_ALIGN_SIZE - 1)) || (a.used_user_addr & (VRING_USED_ALIGN_SIZE - 1)) || (a.log_guest_addr & (VRING_USED_ALIGN_SIZE - 1))) { r = -EINVAL; break; } /* We only verify access here if backend is configured. * If it is not, we don't as size might not have been setup. * We will verify when backend is configured. */ if (vq->private_data) { if (!vq_access_ok(vq, vq->num, (void __user *)(unsigned long)a.desc_user_addr, (void __user *)(unsigned long)a.avail_user_addr, (void __user *)(unsigned long)a.used_user_addr)) { r = -EINVAL; break; } /* Also validate log access for used ring if enabled. */ if ((a.flags & (0x1 << VHOST_VRING_F_LOG)) && !log_access_ok(vq->log_base, a.log_guest_addr, sizeof *vq->used + vq->num * sizeof *vq->used->ring)) { r = -EINVAL; break; } } vq->log_used = !!(a.flags & (0x1 << VHOST_VRING_F_LOG)); vq->desc = (void __user *)(unsigned long)a.desc_user_addr; vq->avail = (void __user *)(unsigned long)a.avail_user_addr; vq->log_addr = a.log_guest_addr; vq->used = (void __user *)(unsigned long)a.used_user_addr; break; case VHOST_SET_VRING_KICK: if (copy_from_user(&f, argp, sizeof f)) { r = -EFAULT; break; } eventfp = f.fd == -1 ? NULL : eventfd_fget(f.fd); if (IS_ERR(eventfp)) { r = PTR_ERR(eventfp); break; } if (eventfp != vq->kick) { pollstop = (filep = vq->kick) != NULL; pollstart = (vq->kick = eventfp) != NULL; } else filep = eventfp; break; case VHOST_SET_VRING_CALL: if (copy_from_user(&f, argp, sizeof f)) { r = -EFAULT; break; } eventfp = f.fd == -1 ? NULL : eventfd_fget(f.fd); if (IS_ERR(eventfp)) { r = PTR_ERR(eventfp); break; } if (eventfp != vq->call) { filep = vq->call; ctx = vq->call_ctx; vq->call = eventfp; vq->call_ctx = eventfp ? eventfd_ctx_fileget(eventfp) : NULL; } else filep = eventfp; break; case VHOST_SET_VRING_ERR: if (copy_from_user(&f, argp, sizeof f)) { r = -EFAULT; break; } eventfp = f.fd == -1 ? NULL : eventfd_fget(f.fd); if (IS_ERR(eventfp)) { r = PTR_ERR(eventfp); break; } if (eventfp != vq->error) { filep = vq->error; vq->error = eventfp; ctx = vq->error_ctx; vq->error_ctx = eventfp ? eventfd_ctx_fileget(eventfp) : NULL; } else filep = eventfp; break; case VHOST_SET_VRING_ENDIAN: r = vhost_set_vring_endian(vq, argp); break; case VHOST_GET_VRING_ENDIAN: r = vhost_get_vring_endian(vq, idx, argp); break; default: r = -ENOIOCTLCMD; } if (pollstop && vq->handle_kick) vhost_poll_stop(&vq->poll); if (ctx) eventfd_ctx_put(ctx); if (filep) fput(filep); if (pollstart && vq->handle_kick) r = vhost_poll_start(&vq->poll, vq->kick); mutex_unlock(&vq->mutex); if (pollstop && vq->handle_kick) vhost_poll_flush(&vq->poll); return r; } EXPORT_SYMBOL_GPL(vhost_vring_ioctl); /* Caller must have device mutex */ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp) { struct file *eventfp, *filep = NULL; struct eventfd_ctx *ctx = NULL; u64 p; long r; int i, fd; /* If you are not the owner, you can become one */ if (ioctl == VHOST_SET_OWNER) { r = vhost_dev_set_owner(d); goto done; } /* You must be the owner to do anything else */ r = vhost_dev_check_owner(d); if (r) goto done; switch (ioctl) { case VHOST_SET_MEM_TABLE: r = vhost_set_memory(d, argp); break; case VHOST_SET_LOG_BASE: if (copy_from_user(&p, argp, sizeof p)) { r = -EFAULT; break; } if ((u64)(unsigned long)p != p) { r = -EFAULT; break; } for (i = 0; i < d->nvqs; ++i) { struct vhost_virtqueue *vq; void __user *base = (void __user *)(unsigned long)p; vq = d->vqs[i]; mutex_lock(&vq->mutex); /* If ring is inactive, will check when it's enabled. */ if (vq->private_data && !vq_log_access_ok(vq, base)) r = -EFAULT; else vq->log_base = base; mutex_unlock(&vq->mutex); } break; case VHOST_SET_LOG_FD: r = get_user(fd, (int __user *)argp); if (r < 0) break; eventfp = fd == -1 ? NULL : eventfd_fget(fd); if (IS_ERR(eventfp)) { r = PTR_ERR(eventfp); break; } if (eventfp != d->log_file) { filep = d->log_file; d->log_file = eventfp; ctx = d->log_ctx; d->log_ctx = eventfp ? eventfd_ctx_fileget(eventfp) : NULL; } else filep = eventfp; for (i = 0; i < d->nvqs; ++i) { mutex_lock(&d->vqs[i]->mutex); d->vqs[i]->log_ctx = d->log_ctx; mutex_unlock(&d->vqs[i]->mutex); } if (ctx) eventfd_ctx_put(ctx); if (filep) fput(filep); break; default: r = -ENOIOCTLCMD; break; } done: return r; } EXPORT_SYMBOL_GPL(vhost_dev_ioctl); static const struct vhost_memory_region *find_region(struct vhost_memory *mem, __u64 addr, __u32 len) { const struct vhost_memory_region *reg; int start = 0, end = mem->nregions; while (start < end) { int slot = start + (end - start) / 2; reg = mem->regions + slot; if (addr >= reg->guest_phys_addr) end = slot; else start = slot + 1; } reg = mem->regions + start; if (addr >= reg->guest_phys_addr && reg->guest_phys_addr + reg->memory_size > addr) return reg; return NULL; } /* TODO: This is really inefficient. We need something like get_user() * (instruction directly accesses the data, with an exception table entry * returning -EFAULT). See Documentation/x86/exception-tables.txt. */ static int set_bit_to_user(int nr, void __user *addr) { unsigned long log = (unsigned long)addr; struct page *page; void *base; int bit = nr + (log % PAGE_SIZE) * 8; int r; r = get_user_pages_fast(log, 1, 1, &page); if (r < 0) return r; BUG_ON(r != 1); base = kmap_atomic(page); set_bit(bit, base); kunmap_atomic(base); set_page_dirty_lock(page); put_page(page); return 0; } static int log_write(void __user *log_base, u64 write_address, u64 write_length) { u64 write_page = write_address / VHOST_PAGE_SIZE; int r; if (!write_length) return 0; write_length += write_address % VHOST_PAGE_SIZE; for (;;) { u64 base = (u64)(unsigned long)log_base; u64 log = base + write_page / 8; int bit = write_page % 8; if ((u64)(unsigned long)log != log) return -EFAULT; r = set_bit_to_user(bit, (void __user *)(unsigned long)log); if (r < 0) return r; if (write_length <= VHOST_PAGE_SIZE) break; write_length -= VHOST_PAGE_SIZE; write_page += 1; } return r; } int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log, unsigned int log_num, u64 len) { int i, r; /* Make sure data written is seen before log. */ smp_wmb(); for (i = 0; i < log_num; ++i) { u64 l = min(log[i].len, len); r = log_write(vq->log_base, log[i].addr, l); if (r < 0) return r; len -= l; if (!len) { if (vq->log_ctx) eventfd_signal(vq->log_ctx, 1); return 0; } } /* Length written exceeds what we have stored. This is a bug. */ BUG(); return 0; } EXPORT_SYMBOL_GPL(vhost_log_write); static int vhost_update_used_flags(struct vhost_virtqueue *vq) { void __user *used; if (__put_user(cpu_to_vhost16(vq, vq->used_flags), &vq->used->flags) < 0) return -EFAULT; if (unlikely(vq->log_used)) { /* Make sure the flag is seen before log. */ smp_wmb(); /* Log used flag write. */ used = &vq->used->flags; log_write(vq->log_base, vq->log_addr + (used - (void __user *)vq->used), sizeof vq->used->flags); if (vq->log_ctx) eventfd_signal(vq->log_ctx, 1); } return 0; } static int vhost_update_avail_event(struct vhost_virtqueue *vq, u16 avail_event) { if (__put_user(cpu_to_vhost16(vq, vq->avail_idx), vhost_avail_event(vq))) return -EFAULT; if (unlikely(vq->log_used)) { void __user *used; /* Make sure the event is seen before log. */ smp_wmb(); /* Log avail event write */ used = vhost_avail_event(vq); log_write(vq->log_base, vq->log_addr + (used - (void __user *)vq->used), sizeof *vhost_avail_event(vq)); if (vq->log_ctx) eventfd_signal(vq->log_ctx, 1); } return 0; } int vhost_vq_init_access(struct vhost_virtqueue *vq) { __virtio16 last_used_idx; int r; bool is_le = vq->is_le; if (!vq->private_data) { vhost_reset_is_le(vq); return 0; } vhost_init_is_le(vq); r = vhost_update_used_flags(vq); if (r) goto err; vq->signalled_used_valid = false; if (!access_ok(VERIFY_READ, &vq->used->idx, sizeof vq->used->idx)) { r = -EFAULT; goto err; } r = __get_user(last_used_idx, &vq->used->idx); if (r) goto err; vq->last_used_idx = vhost16_to_cpu(vq, last_used_idx); return 0; err: vq->is_le = is_le; return r; } EXPORT_SYMBOL_GPL(vhost_vq_init_access); static int translate_desc(struct vhost_virtqueue *vq, u64 addr, u32 len, struct iovec iov[], int iov_size) { const struct vhost_memory_region *reg; struct vhost_memory *mem; struct iovec *_iov; u64 s = 0; int ret = 0; mem = vq->memory; while ((u64)len > s) { u64 size; if (unlikely(ret >= iov_size)) { ret = -ENOBUFS; break; } reg = find_region(mem, addr, len); if (unlikely(!reg)) { ret = -EFAULT; break; } _iov = iov + ret; size = reg->memory_size - addr + reg->guest_phys_addr; _iov->iov_len = min((u64)len - s, size); _iov->iov_base = (void __user *)(unsigned long) (reg->userspace_addr + addr - reg->guest_phys_addr); s += size; addr += size; ++ret; } return ret; } /* Each buffer in the virtqueues is actually a chain of descriptors. This * function returns the next descriptor in the chain, * or -1U if we're at the end. */ static unsigned next_desc(struct vhost_virtqueue *vq, struct vring_desc *desc) { unsigned int next; /* If this descriptor says it doesn't chain, we're done. */ if (!(desc->flags & cpu_to_vhost16(vq, VRING_DESC_F_NEXT))) return -1U; /* Check they're not leading us off end of descriptors. */ next = vhost16_to_cpu(vq, desc->next); /* Make sure compiler knows to grab that: we don't want it changing! */ /* We will use the result as an index in an array, so most * architectures only need a compiler barrier here. */ read_barrier_depends(); return next; } static int get_indirect(struct vhost_virtqueue *vq, struct iovec iov[], unsigned int iov_size, unsigned int *out_num, unsigned int *in_num, struct vhost_log *log, unsigned int *log_num, struct vring_desc *indirect) { struct vring_desc desc; unsigned int i = 0, count, found = 0; u32 len = vhost32_to_cpu(vq, indirect->len); struct iov_iter from; int ret; /* Sanity check */ if (unlikely(len % sizeof desc)) { vq_err(vq, "Invalid length in indirect descriptor: " "len 0x%llx not multiple of 0x%zx\n", (unsigned long long)len, sizeof desc); return -EINVAL; } ret = translate_desc(vq, vhost64_to_cpu(vq, indirect->addr), len, vq->indirect, UIO_MAXIOV); if (unlikely(ret < 0)) { vq_err(vq, "Translation failure %d in indirect.\n", ret); return ret; } iov_iter_init(&from, READ, vq->indirect, ret, len); /* We will use the result as an address to read from, so most * architectures only need a compiler barrier here. */ read_barrier_depends(); count = len / sizeof desc; /* Buffers are chained via a 16 bit next field, so * we can have at most 2^16 of these. */ if (unlikely(count > USHRT_MAX + 1)) { vq_err(vq, "Indirect buffer length too big: %d\n", indirect->len); return -E2BIG; } do { unsigned iov_count = *in_num + *out_num; if (unlikely(++found > count)) { vq_err(vq, "Loop detected: last one at %u " "indirect size %u\n", i, count); return -EINVAL; } if (unlikely(copy_from_iter(&desc, sizeof(desc), &from) != sizeof(desc))) { vq_err(vq, "Failed indirect descriptor: idx %d, %zx\n", i, (size_t)vhost64_to_cpu(vq, indirect->addr) + i * sizeof desc); return -EINVAL; } if (unlikely(desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_INDIRECT))) { vq_err(vq, "Nested indirect descriptor: idx %d, %zx\n", i, (size_t)vhost64_to_cpu(vq, indirect->addr) + i * sizeof desc); return -EINVAL; } ret = translate_desc(vq, vhost64_to_cpu(vq, desc.addr), vhost32_to_cpu(vq, desc.len), iov + iov_count, iov_size - iov_count); if (unlikely(ret < 0)) { vq_err(vq, "Translation failure %d indirect idx %d\n", ret, i); return ret; } /* If this is an input descriptor, increment that count. */ if (desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_WRITE)) { *in_num += ret; if (unlikely(log)) { log[*log_num].addr = vhost64_to_cpu(vq, desc.addr); log[*log_num].len = vhost32_to_cpu(vq, desc.len); ++*log_num; } } else { /* If it's an output descriptor, they're all supposed * to come before any input descriptors. */ if (unlikely(*in_num)) { vq_err(vq, "Indirect descriptor " "has out after in: idx %d\n", i); return -EINVAL; } *out_num += ret; } } while ((i = next_desc(vq, &desc)) != -1); return 0; } /* This looks in the virtqueue and for the first available buffer, and converts * it to an iovec for convenient access. Since descriptors consist of some * number of output then some number of input descriptors, it's actually two * iovecs, but we pack them into one and note how many of each there were. * * This function returns the descriptor number found, or vq->num (which is * never a valid descriptor number) if none was found. A negative code is * returned on error. */ int vhost_get_vq_desc(struct vhost_virtqueue *vq, struct iovec iov[], unsigned int iov_size, unsigned int *out_num, unsigned int *in_num, struct vhost_log *log, unsigned int *log_num) { struct vring_desc desc; unsigned int i, head, found = 0; u16 last_avail_idx; __virtio16 avail_idx; __virtio16 ring_head; int ret; /* Check it isn't doing very strange things with descriptor numbers. */ last_avail_idx = vq->last_avail_idx; if (unlikely(__get_user(avail_idx, &vq->avail->idx))) { vq_err(vq, "Failed to access avail idx at %p\n", &vq->avail->idx); return -EFAULT; } vq->avail_idx = vhost16_to_cpu(vq, avail_idx); if (unlikely((u16)(vq->avail_idx - last_avail_idx) > vq->num)) { vq_err(vq, "Guest moved used index from %u to %u", last_avail_idx, vq->avail_idx); return -EFAULT; } /* If there's nothing new since last we looked, return invalid. */ if (vq->avail_idx == last_avail_idx) return vq->num; /* Only get avail ring entries after they have been exposed by guest. */ smp_rmb(); /* Grab the next descriptor number they're advertising, and increment * the index we've seen. */ if (unlikely(__get_user(ring_head, &vq->avail->ring[last_avail_idx & (vq->num - 1)]))) { vq_err(vq, "Failed to read head: idx %d address %p\n", last_avail_idx, &vq->avail->ring[last_avail_idx % vq->num]); return -EFAULT; } head = vhost16_to_cpu(vq, ring_head); /* If their number is silly, that's an error. */ if (unlikely(head >= vq->num)) { vq_err(vq, "Guest says index %u > %u is available", head, vq->num); return -EINVAL; } /* When we start there are none of either input nor output. */ *out_num = *in_num = 0; if (unlikely(log)) *log_num = 0; i = head; do { unsigned iov_count = *in_num + *out_num; if (unlikely(i >= vq->num)) { vq_err(vq, "Desc index is %u > %u, head = %u", i, vq->num, head); return -EINVAL; } if (unlikely(++found > vq->num)) { vq_err(vq, "Loop detected: last one at %u " "vq size %u head %u\n", i, vq->num, head); return -EINVAL; } ret = __copy_from_user(&desc, vq->desc + i, sizeof desc); if (unlikely(ret)) { vq_err(vq, "Failed to get descriptor: idx %d addr %p\n", i, vq->desc + i); return -EFAULT; } if (desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_INDIRECT)) { ret = get_indirect(vq, iov, iov_size, out_num, in_num, log, log_num, &desc); if (unlikely(ret < 0)) { vq_err(vq, "Failure detected " "in indirect descriptor at idx %d\n", i); return ret; } continue; } ret = translate_desc(vq, vhost64_to_cpu(vq, desc.addr), vhost32_to_cpu(vq, desc.len), iov + iov_count, iov_size - iov_count); if (unlikely(ret < 0)) { vq_err(vq, "Translation failure %d descriptor idx %d\n", ret, i); return ret; } if (desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_WRITE)) { /* If this is an input descriptor, * increment that count. */ *in_num += ret; if (unlikely(log)) { log[*log_num].addr = vhost64_to_cpu(vq, desc.addr); log[*log_num].len = vhost32_to_cpu(vq, desc.len); ++*log_num; } } else { /* If it's an output descriptor, they're all supposed * to come before any input descriptors. */ if (unlikely(*in_num)) { vq_err(vq, "Descriptor has out after in: " "idx %d\n", i); return -EINVAL; } *out_num += ret; } } while ((i = next_desc(vq, &desc)) != -1); /* On success, increment avail index. */ vq->last_avail_idx++; /* Assume notifications from guest are disabled at this point, * if they aren't we would need to update avail_event index. */ BUG_ON(!(vq->used_flags & VRING_USED_F_NO_NOTIFY)); return head; } EXPORT_SYMBOL_GPL(vhost_get_vq_desc); /* Reverse the effect of vhost_get_vq_desc. Useful for error handling. */ void vhost_discard_vq_desc(struct vhost_virtqueue *vq, int n) { vq->last_avail_idx -= n; } EXPORT_SYMBOL_GPL(vhost_discard_vq_desc); /* After we've used one of their buffers, we tell them about it. We'll then * want to notify the guest, using eventfd. */ int vhost_add_used(struct vhost_virtqueue *vq, unsigned int head, int len) { struct vring_used_elem heads = { cpu_to_vhost32(vq, head), cpu_to_vhost32(vq, len) }; return vhost_add_used_n(vq, &heads, 1); } EXPORT_SYMBOL_GPL(vhost_add_used); static int __vhost_add_used_n(struct vhost_virtqueue *vq, struct vring_used_elem *heads, unsigned count) { struct vring_used_elem __user *used; u16 old, new; int start; start = vq->last_used_idx & (vq->num - 1); used = vq->used->ring + start; if (count == 1) { if (__put_user(heads[0].id, &used->id)) { vq_err(vq, "Failed to write used id"); return -EFAULT; } if (__put_user(heads[0].len, &used->len)) { vq_err(vq, "Failed to write used len"); return -EFAULT; } } else if (__copy_to_user(used, heads, count * sizeof *used)) { vq_err(vq, "Failed to write used"); return -EFAULT; } if (unlikely(vq->log_used)) { /* Make sure data is seen before log. */ smp_wmb(); /* Log used ring entry write. */ log_write(vq->log_base, vq->log_addr + ((void __user *)used - (void __user *)vq->used), count * sizeof *used); } old = vq->last_used_idx; new = (vq->last_used_idx += count); /* If the driver never bothers to signal in a very long while, * used index might wrap around. If that happens, invalidate * signalled_used index we stored. TODO: make sure driver * signals at least once in 2^16 and remove this. */ if (unlikely((u16)(new - vq->signalled_used) < (u16)(new - old))) vq->signalled_used_valid = false; return 0; } /* After we've used one of their buffers, we tell them about it. We'll then * want to notify the guest, using eventfd. */ int vhost_add_used_n(struct vhost_virtqueue *vq, struct vring_used_elem *heads, unsigned count) { int start, n, r; start = vq->last_used_idx & (vq->num - 1); n = vq->num - start; if (n < count) { r = __vhost_add_used_n(vq, heads, n); if (r < 0) return r; heads += n; count -= n; } r = __vhost_add_used_n(vq, heads, count); /* Make sure buffer is written before we update index. */ smp_wmb(); if (__put_user(cpu_to_vhost16(vq, vq->last_used_idx), &vq->used->idx)) { vq_err(vq, "Failed to increment used idx"); return -EFAULT; } if (unlikely(vq->log_used)) { /* Log used index update. */ log_write(vq->log_base, vq->log_addr + offsetof(struct vring_used, idx), sizeof vq->used->idx); if (vq->log_ctx) eventfd_signal(vq->log_ctx, 1); } return r; } EXPORT_SYMBOL_GPL(vhost_add_used_n); static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq) { __u16 old, new; __virtio16 event; bool v; /* Flush out used index updates. This is paired * with the barrier that the Guest executes when enabling * interrupts. */ smp_mb(); if (vhost_has_feature(vq, VIRTIO_F_NOTIFY_ON_EMPTY) && unlikely(vq->avail_idx == vq->last_avail_idx)) return true; if (!vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX)) { __virtio16 flags; if (__get_user(flags, &vq->avail->flags)) { vq_err(vq, "Failed to get flags"); return true; } return !(flags & cpu_to_vhost16(vq, VRING_AVAIL_F_NO_INTERRUPT)); } old = vq->signalled_used; v = vq->signalled_used_valid; new = vq->signalled_used = vq->last_used_idx; vq->signalled_used_valid = true; if (unlikely(!v)) return true; if (__get_user(event, vhost_used_event(vq))) { vq_err(vq, "Failed to get used event idx"); return true; } return vring_need_event(vhost16_to_cpu(vq, event), new, old); } /* This actually signals the guest, using eventfd. */ void vhost_signal(struct vhost_dev *dev, struct vhost_virtqueue *vq) { /* Signal the Guest tell them we used something up. */ if (vq->call_ctx && vhost_notify(dev, vq)) eventfd_signal(vq->call_ctx, 1); } EXPORT_SYMBOL_GPL(vhost_signal); /* And here's the combo meal deal. Supersize me! */ void vhost_add_used_and_signal(struct vhost_dev *dev, struct vhost_virtqueue *vq, unsigned int head, int len) { vhost_add_used(vq, head, len); vhost_signal(dev, vq); } EXPORT_SYMBOL_GPL(vhost_add_used_and_signal); /* multi-buffer version of vhost_add_used_and_signal */ void vhost_add_used_and_signal_n(struct vhost_dev *dev, struct vhost_virtqueue *vq, struct vring_used_elem *heads, unsigned count) { vhost_add_used_n(vq, heads, count); vhost_signal(dev, vq); } EXPORT_SYMBOL_GPL(vhost_add_used_and_signal_n); /* return true if we're sure that avaiable ring is empty */ bool vhost_vq_avail_empty(struct vhost_dev *dev, struct vhost_virtqueue *vq) { __virtio16 avail_idx; int r; r = __get_user(avail_idx, &vq->avail->idx); if (r) return false; return vhost16_to_cpu(vq, avail_idx) == vq->avail_idx; } EXPORT_SYMBOL_GPL(vhost_vq_avail_empty); /* OK, now we need to know about added descriptors. */ bool vhost_enable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq) { __virtio16 avail_idx; int r; if (!(vq->used_flags & VRING_USED_F_NO_NOTIFY)) return false; vq->used_flags &= ~VRING_USED_F_NO_NOTIFY; if (!vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX)) { r = vhost_update_used_flags(vq); if (r) { vq_err(vq, "Failed to enable notification at %p: %d\n", &vq->used->flags, r); return false; } } else { r = vhost_update_avail_event(vq, vq->avail_idx); if (r) { vq_err(vq, "Failed to update avail event index at %p: %d\n", vhost_avail_event(vq), r); return false; } } /* They could have slipped one in as we were doing that: make * sure it's written, then check again. */ smp_mb(); r = __get_user(avail_idx, &vq->avail->idx); if (r) { vq_err(vq, "Failed to check avail idx at %p: %d\n", &vq->avail->idx, r); return false; } return vhost16_to_cpu(vq, avail_idx) != vq->avail_idx; } EXPORT_SYMBOL_GPL(vhost_enable_notify); /* We don't need to be notified again. */ void vhost_disable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq) { int r; if (vq->used_flags & VRING_USED_F_NO_NOTIFY) return; vq->used_flags |= VRING_USED_F_NO_NOTIFY; if (!vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX)) { r = vhost_update_used_flags(vq); if (r) vq_err(vq, "Failed to enable notification at %p: %d\n", &vq->used->flags, r); } } EXPORT_SYMBOL_GPL(vhost_disable_notify); static int __init vhost_init(void) { return 0; } static void __exit vhost_exit(void) { } module_init(vhost_init); module_exit(vhost_exit); MODULE_VERSION("0.0.1"); MODULE_LICENSE("GPL v2"); MODULE_AUTHOR("Michael S. Tsirkin"); MODULE_DESCRIPTION("Host kernel accelerator for virtio");