/* Virtio ring implementation. * * Copyright 2007 Rusty Russell IBM Corporation * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */ #include <linux/virtio.h> #include <linux/virtio_ring.h> #include <linux/virtio_config.h> #include <linux/device.h> #include <linux/slab.h> /* virtio guest is communicating with a virtual "device" that actually runs on * a host processor. Memory barriers are used to control SMP effects. */ #ifdef CONFIG_SMP /* Where possible, use SMP barriers which are more lightweight than mandatory * barriers, because mandatory barriers control MMIO effects on accesses * through relaxed memory I/O windows (which virtio does not use). */ #define virtio_mb() smp_mb() #define virtio_rmb() smp_rmb() #define virtio_wmb() smp_wmb() #else /* We must force memory ordering even if guest is UP since host could be * running on another CPU, but SMP barriers are defined to barrier() in that * configuration. So fall back to mandatory barriers instead. */ #define virtio_mb() mb() #define virtio_rmb() rmb() #define virtio_wmb() wmb() #endif #ifdef DEBUG /* For development, we want to crash whenever the ring is screwed. */ #define BAD_RING(_vq, fmt, args...) \ do { \ dev_err(&(_vq)->vq.vdev->dev, \ "%s:"fmt, (_vq)->vq.name, ##args); \ BUG(); \ } while (0) /* Caller is supposed to guarantee no reentry. */ #define START_USE(_vq) \ do { \ if ((_vq)->in_use) \ panic("%s:in_use = %i\n", \ (_vq)->vq.name, (_vq)->in_use); \ (_vq)->in_use = __LINE__; \ } while (0) #define END_USE(_vq) \ do { BUG_ON(!(_vq)->in_use); (_vq)->in_use = 0; } while(0) #else #define BAD_RING(_vq, fmt, args...) \ do { \ dev_err(&_vq->vq.vdev->dev, \ "%s:"fmt, (_vq)->vq.name, ##args); \ (_vq)->broken = true; \ } while (0) #define START_USE(vq) #define END_USE(vq) #endif struct vring_virtqueue { struct virtqueue vq; /* Actual memory layout for this queue */ struct vring vring; /* Other side has made a mess, don't try any more. */ bool broken; /* Host supports indirect buffers */ bool indirect; /* Host publishes avail event idx */ bool event; /* Number of free buffers */ unsigned int num_free; /* Head of free buffer list. */ unsigned int free_head; /* Number we've added since last sync. */ unsigned int num_added; /* Last used index we've seen. */ u16 last_used_idx; /* How to notify other side. FIXME: commonalize hcalls! */ void (*notify)(struct virtqueue *vq); #ifdef DEBUG /* They're supposed to lock for us. */ unsigned int in_use; #endif /* Tokens for callbacks. */ void *data[]; }; #define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq) /* Set up an indirect table of descriptors and add it to the queue. */ static int vring_add_indirect(struct vring_virtqueue *vq, struct scatterlist sg[], unsigned int out, unsigned int in, gfp_t gfp) { struct vring_desc *desc; unsigned head; int i; desc = kmalloc((out + in) * sizeof(struct vring_desc), gfp); if (!desc) return -ENOMEM; /* Transfer entries from the sg list into the indirect page */ for (i = 0; i < out; i++) { desc[i].flags = VRING_DESC_F_NEXT; desc[i].addr = sg_phys(sg); desc[i].len = sg->length; desc[i].next = i+1; sg++; } for (; i < (out + in); i++) { desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE; desc[i].addr = sg_phys(sg); desc[i].len = sg->length; desc[i].next = i+1; sg++; } /* Last one doesn't continue. */ desc[i-1].flags &= ~VRING_DESC_F_NEXT; desc[i-1].next = 0; /* We're about to use a buffer */ vq->num_free--; /* Use a single buffer which doesn't continue */ head = vq->free_head; vq->vring.desc[head].flags = VRING_DESC_F_INDIRECT; vq->vring.desc[head].addr = virt_to_phys(desc); vq->vring.desc[head].len = i * sizeof(struct vring_desc); /* Update free pointer */ vq->free_head = vq->vring.desc[head].next; return head; } int virtqueue_add_buf_gfp(struct virtqueue *_vq, struct scatterlist sg[], unsigned int out, unsigned int in, void *data, gfp_t gfp) { struct vring_virtqueue *vq = to_vvq(_vq); unsigned int i, avail, uninitialized_var(prev); int head; START_USE(vq); BUG_ON(data == NULL); /* If the host supports indirect descriptor tables, and we have multiple * buffers, then go indirect. FIXME: tune this threshold */ if (vq->indirect && (out + in) > 1 && vq->num_free) { head = vring_add_indirect(vq, sg, out, in, gfp); if (likely(head >= 0)) goto add_head; } BUG_ON(out + in > vq->vring.num); BUG_ON(out + in == 0); if (vq->num_free < out + in) { pr_debug("Can't add buf len %i - avail = %i\n", out + in, vq->num_free); /* FIXME: for historical reasons, we force a notify here if * there are outgoing parts to the buffer. Presumably the * host should service the ring ASAP. */ if (out) vq->notify(&vq->vq); END_USE(vq); return -ENOSPC; } /* We're about to use some buffers from the free list. */ vq->num_free -= out + in; head = vq->free_head; for (i = vq->free_head; out; i = vq->vring.desc[i].next, out--) { vq->vring.desc[i].flags = VRING_DESC_F_NEXT; vq->vring.desc[i].addr = sg_phys(sg); vq->vring.desc[i].len = sg->length; prev = i; sg++; } for (; in; i = vq->vring.desc[i].next, in--) { vq->vring.desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE; vq->vring.desc[i].addr = sg_phys(sg); vq->vring.desc[i].len = sg->length; prev = i; sg++; } /* Last one doesn't continue. */ vq->vring.desc[prev].flags &= ~VRING_DESC_F_NEXT; /* Update free pointer */ vq->free_head = i; add_head: /* Set token. */ vq->data[head] = data; /* Put entry in available array (but don't update avail->idx until they * do sync). FIXME: avoid modulus here? */ avail = (vq->vring.avail->idx + vq->num_added++) % vq->vring.num; vq->vring.avail->ring[avail] = head; pr_debug("Added buffer head %i to %p\n", head, vq); END_USE(vq); return vq->num_free; } EXPORT_SYMBOL_GPL(virtqueue_add_buf_gfp); void virtqueue_kick(struct virtqueue *_vq) { struct vring_virtqueue *vq = to_vvq(_vq); u16 new, old; START_USE(vq); /* Descriptors and available array need to be set before we expose the * new available array entries. */ virtio_wmb(); old = vq->vring.avail->idx; new = vq->vring.avail->idx = old + vq->num_added; vq->num_added = 0; /* Need to update avail index before checking if we should notify */ virtio_mb(); if (vq->event ? vring_need_event(vring_avail_event(&vq->vring), new, old) : !(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY)) /* Prod other side to tell it about changes. */ vq->notify(&vq->vq); END_USE(vq); } EXPORT_SYMBOL_GPL(virtqueue_kick); static void detach_buf(struct vring_virtqueue *vq, unsigned int head) { unsigned int i; /* Clear data ptr. */ vq->data[head] = NULL; /* Put back on free list: find end */ i = head; /* Free the indirect table */ if (vq->vring.desc[i].flags & VRING_DESC_F_INDIRECT) kfree(phys_to_virt(vq->vring.desc[i].addr)); while (vq->vring.desc[i].flags & VRING_DESC_F_NEXT) { i = vq->vring.desc[i].next; vq->num_free++; } vq->vring.desc[i].next = vq->free_head; vq->free_head = head; /* Plus final descriptor */ vq->num_free++; } static inline bool more_used(const struct vring_virtqueue *vq) { return vq->last_used_idx != vq->vring.used->idx; } void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len) { struct vring_virtqueue *vq = to_vvq(_vq); void *ret; unsigned int i; START_USE(vq); if (unlikely(vq->broken)) { END_USE(vq); return NULL; } if (!more_used(vq)) { pr_debug("No more buffers in queue\n"); END_USE(vq); return NULL; } /* Only get used array entries after they have been exposed by host. */ virtio_rmb(); i = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].id; *len = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].len; if (unlikely(i >= vq->vring.num)) { BAD_RING(vq, "id %u out of range\n", i); return NULL; } if (unlikely(!vq->data[i])) { BAD_RING(vq, "id %u is not a head!\n", i); return NULL; } /* detach_buf clears data, so grab it now. */ ret = vq->data[i]; detach_buf(vq, i); vq->last_used_idx++; /* If we expect an interrupt for the next entry, tell host * by writing event index and flush out the write before * the read in the next get_buf call. */ if (!(vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT)) { vring_used_event(&vq->vring) = vq->last_used_idx; virtio_mb(); } END_USE(vq); return ret; } EXPORT_SYMBOL_GPL(virtqueue_get_buf); void virtqueue_disable_cb(struct virtqueue *_vq) { struct vring_virtqueue *vq = to_vvq(_vq); vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT; } EXPORT_SYMBOL_GPL(virtqueue_disable_cb); bool virtqueue_enable_cb(struct virtqueue *_vq) { struct vring_virtqueue *vq = to_vvq(_vq); START_USE(vq); /* We optimistically turn back on interrupts, then check if there was * more to do. */ /* Depending on the VIRTIO_RING_F_EVENT_IDX feature, we need to * either clear the flags bit or point the event index at the next * entry. Always do both to keep code simple. */ vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT; vring_used_event(&vq->vring) = vq->last_used_idx; virtio_mb(); if (unlikely(more_used(vq))) { END_USE(vq); return false; } END_USE(vq); return true; } EXPORT_SYMBOL_GPL(virtqueue_enable_cb); bool virtqueue_enable_cb_delayed(struct virtqueue *_vq) { struct vring_virtqueue *vq = to_vvq(_vq); u16 bufs; START_USE(vq); /* We optimistically turn back on interrupts, then check if there was * more to do. */ /* Depending on the VIRTIO_RING_F_USED_EVENT_IDX feature, we need to * either clear the flags bit or point the event index at the next * entry. Always do both to keep code simple. */ vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT; /* TODO: tune this threshold */ bufs = (u16)(vq->vring.avail->idx - vq->last_used_idx) * 3 / 4; vring_used_event(&vq->vring) = vq->last_used_idx + bufs; virtio_mb(); if (unlikely((u16)(vq->vring.used->idx - vq->last_used_idx) > bufs)) { END_USE(vq); return false; } END_USE(vq); return true; } EXPORT_SYMBOL_GPL(virtqueue_enable_cb_delayed); void *virtqueue_detach_unused_buf(struct virtqueue *_vq) { struct vring_virtqueue *vq = to_vvq(_vq); unsigned int i; void *buf; START_USE(vq); for (i = 0; i < vq->vring.num; i++) { if (!vq->data[i]) continue; /* detach_buf clears data, so grab it now. */ buf = vq->data[i]; detach_buf(vq, i); vq->vring.avail->idx--; END_USE(vq); return buf; } /* That should have freed everything. */ BUG_ON(vq->num_free != vq->vring.num); END_USE(vq); return NULL; } EXPORT_SYMBOL_GPL(virtqueue_detach_unused_buf); irqreturn_t vring_interrupt(int irq, void *_vq) { struct vring_virtqueue *vq = to_vvq(_vq); if (!more_used(vq)) { pr_debug("virtqueue interrupt with no work for %p\n", vq); return IRQ_NONE; } if (unlikely(vq->broken)) return IRQ_HANDLED; pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback); if (vq->vq.callback) vq->vq.callback(&vq->vq); return IRQ_HANDLED; } EXPORT_SYMBOL_GPL(vring_interrupt); struct virtqueue *vring_new_virtqueue(unsigned int num, unsigned int vring_align, struct virtio_device *vdev, void *pages, void (*notify)(struct virtqueue *), void (*callback)(struct virtqueue *), const char *name) { struct vring_virtqueue *vq; unsigned int i; /* We assume num is a power of 2. */ if (num & (num - 1)) { dev_warn(&vdev->dev, "Bad virtqueue length %u\n", num); return NULL; } vq = kmalloc(sizeof(*vq) + sizeof(void *)*num, GFP_KERNEL); if (!vq) return NULL; vring_init(&vq->vring, num, pages, vring_align); vq->vq.callback = callback; vq->vq.vdev = vdev; vq->vq.name = name; vq->notify = notify; vq->broken = false; vq->last_used_idx = 0; vq->num_added = 0; list_add_tail(&vq->vq.list, &vdev->vqs); #ifdef DEBUG vq->in_use = false; #endif vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC); vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX); /* No callback? Tell other side not to bother us. */ if (!callback) vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT; /* Put everything in free lists. */ vq->num_free = num; vq->free_head = 0; for (i = 0; i < num-1; i++) { vq->vring.desc[i].next = i+1; vq->data[i] = NULL; } vq->data[i] = NULL; return &vq->vq; } EXPORT_SYMBOL_GPL(vring_new_virtqueue); void vring_del_virtqueue(struct virtqueue *vq) { list_del(&vq->list); kfree(to_vvq(vq)); } EXPORT_SYMBOL_GPL(vring_del_virtqueue); /* Manipulates transport-specific feature bits. */ void vring_transport_features(struct virtio_device *vdev) { unsigned int i; for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++) { switch (i) { case VIRTIO_RING_F_INDIRECT_DESC: break; case VIRTIO_RING_F_EVENT_IDX: break; default: /* We don't understand this bit. */ clear_bit(i, vdev->features); } } } EXPORT_SYMBOL_GPL(vring_transport_features); MODULE_LICENSE("GPL");