virtio_ring.c

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/* 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>
#include <linux/module.h>
#include <linux/hrtimer.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-pci does not use). */
#define virtio_mb(vq) \
    do { if ((vq)->weak_barriers) smp_mb(); else mb(); } while(0)
#define virtio_rmb(vq) \
    do { if ((vq)->weak_barriers) smp_rmb(); else rmb(); } while(0)
#define virtio_wmb(vq) \
    do { if ((vq)->weak_barriers) smp_wmb(); else wmb(); } while(0)
#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(vq) mb()
#define virtio_rmb(vq) rmb()
#define virtio_wmb(vq) 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;

    /* Can we use weak barriers? */
    bool weak_barriers;

    /* 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);

    /* Index of the queue */
    int queue_index;

#ifdef DEBUG
    /* They're supposed to lock for us. */
    unsigned int in_use;

    /* Figure out if their kicks are too delayed. */
    bool last_add_time_valid;
    ktime_t last_add_time;
#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_get_queue_index(struct virtqueue *_vq)
{
    struct vring_virtqueue *vq = to_vvq(_vq);
    return vq->queue_index;
}
EXPORT_SYMBOL_GPL(virtqueue_get_queue_index);

int virtqueue_add_buf(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);

#ifdef DEBUG
    {
        ktime_t now = ktime_get();

        /* No kick or get, with .1 second between?  Warn. */
        if (vq->last_add_time_valid)
            WARN_ON(ktime_to_ms(ktime_sub(now, vq->last_add_time))
                        > 100);
        vq->last_add_time = now;
        vq->last_add_time_valid = true;
    }
#endif

    /* 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). */
    avail = (vq->vring.avail->idx & (vq->vring.num-1));
    vq->vring.avail->ring[avail] = head;

    /* Descriptors and available array need to be set before we expose the
     * new available array entries. */
    virtio_wmb(vq);
    vq->vring.avail->idx++;
    vq->num_added++;

    /* This is very unlikely, but theoretically possible.  Kick
     * just in case. */
    if (unlikely(vq->num_added == (1 << 16) - 1))
        virtqueue_kick(_vq);

    pr_debug("Added buffer head %i to %p\n", head, vq);
    END_USE(vq);

    return vq->num_free;
}
EXPORT_SYMBOL_GPL(virtqueue_add_buf);

bool virtqueue_kick_prepare(struct virtqueue *_vq)
{
    struct vring_virtqueue *vq = to_vvq(_vq);
    u16 new, old;
    bool needs_kick;

    START_USE(vq);
    /* We need to expose available array entries before checking avail
     * event. */
    virtio_mb(vq);

    old = vq->vring.avail->idx - vq->num_added;
    new = vq->vring.avail->idx;
    vq->num_added = 0;

#ifdef DEBUG
    if (vq->last_add_time_valid) {
        WARN_ON(ktime_to_ms(ktime_sub(ktime_get(),
                          vq->last_add_time)) > 100);
    }
    vq->last_add_time_valid = false;
#endif

    if (vq->event) {
        needs_kick = vring_need_event(vring_avail_event(&vq->vring),
                          new, old);
    } else {
        needs_kick = !(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY);
    }
    END_USE(vq);
    return needs_kick;
}
EXPORT_SYMBOL_GPL(virtqueue_kick_prepare);

void virtqueue_notify(struct virtqueue *_vq)
{
    struct vring_virtqueue *vq = to_vvq(_vq);

    /* Prod other side to tell it about changes. */
    vq->notify(_vq);
}
EXPORT_SYMBOL_GPL(virtqueue_notify);

void virtqueue_kick(struct virtqueue *vq)
{
    if (virtqueue_kick_prepare(vq))
        virtqueue_notify(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;
    u16 last_used;

    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(vq);

    last_used = (vq->last_used_idx & (vq->vring.num - 1));
    i = vq->vring.used->ring[last_used].id;
    *len = vq->vring.used->ring[last_used].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(vq);
    }

#ifdef DEBUG
    vq->last_add_time_valid = false;
#endif

    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(vq);
    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(vq);
    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 index,
                      unsigned int num,
                      unsigned int vring_align,
                      struct virtio_device *vdev,
                      bool weak_barriers,
                      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->weak_barriers = weak_barriers;
    vq->broken = false;
    vq->last_used_idx = 0;
    vq->num_added = 0;
    vq->queue_index = index;
    list_add_tail(&vq->vq.list, &vdev->vqs);
#ifdef DEBUG
    vq->in_use = false;
    vq->last_add_time_valid = 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);

unsigned int virtqueue_get_vring_size(struct virtqueue *_vq)
{

    struct vring_virtqueue *vq = to_vvq(_vq);

    return vq->vring.num;
}
EXPORT_SYMBOL_GPL(virtqueue_get_vring_size);

MODULE_LICENSE("GPL");