On Wed, Jun 03, 2020 at 03:13:56PM +0800, Jason Wang wrote:
>
> On 2020/6/2 下午9:05, Michael S. Tsirkin wrote:
> > The idea is to support multiple ring formats by converting
> > to a format-independent array of descriptors.
> >
> > This costs extra cycles, but we gain in ability
> > to fetch a batch of descriptors in one go, which
> > is good for code cache locality.
> >
> > When used, this causes a minor performance degradation,
> > it's been kept as simple as possible for ease of review.
> > A follow-up patch gets us back the performance by adding batching.
> >
> > To simplify benchmarking, I kept the old code around so one can switch
> > back and forth between old and new code. This will go away in the final
> > submission.
> >
> > Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
> > Signed-off-by: Eugenio Pérez <epere...@redhat.com>
> > Link: https://lore.kernel.org/r/20200401183118.8334-2-epere...@redhat.com
> > Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
> > ---
> > drivers/vhost/vhost.c | 297 +++++++++++++++++++++++++++++++++++++++++-
> > drivers/vhost/vhost.h | 16 +++
> > 2 files changed, 312 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > index 96d9871fa0cb..105fc97af2c8 100644
> > --- a/drivers/vhost/vhost.c
> > +++ b/drivers/vhost/vhost.c
> > @@ -298,6 +298,7 @@ static void vhost_vq_reset(struct vhost_dev *dev,
> > struct vhost_virtqueue *vq)
> > {
> > vq->num = 1;
> > + vq->ndescs = 0;
> > vq->desc = NULL;
> > vq->avail = NULL;
> > vq->used = NULL;
> > @@ -368,6 +369,9 @@ static int vhost_worker(void *data)
> > static void vhost_vq_free_iovecs(struct vhost_virtqueue *vq)
> > {
> > + kfree(vq->descs);
> > + vq->descs = NULL;
> > + vq->max_descs = 0;
> > kfree(vq->indirect);
> > vq->indirect = NULL;
> > kfree(vq->log);
> > @@ -384,6 +388,10 @@ static long vhost_dev_alloc_iovecs(struct vhost_dev
> > *dev)
> > for (i = 0; i < dev->nvqs; ++i) {
> > vq = dev->vqs[i];
> > + vq->max_descs = dev->iov_limit;
> > + vq->descs = kmalloc_array(vq->max_descs,
> > + sizeof(*vq->descs),
> > + GFP_KERNEL);
> > vq->indirect = kmalloc_array(UIO_MAXIOV,
> > sizeof(*vq->indirect),
> > GFP_KERNEL);
> > @@ -391,7 +399,7 @@ static long vhost_dev_alloc_iovecs(struct vhost_dev
> > *dev)
> > GFP_KERNEL);
> > vq->heads = kmalloc_array(dev->iov_limit, sizeof(*vq->heads),
> > GFP_KERNEL);
> > - if (!vq->indirect || !vq->log || !vq->heads)
> > + if (!vq->indirect || !vq->log || !vq->heads || !vq->descs)
> > goto err_nomem;
> > }
> > return 0;
> > @@ -2277,6 +2285,293 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
> > }
> > EXPORT_SYMBOL_GPL(vhost_get_vq_desc);
> > +static struct vhost_desc *peek_split_desc(struct vhost_virtqueue *vq)
> > +{
> > + BUG_ON(!vq->ndescs);
> > + return &vq->descs[vq->ndescs - 1];
> > +}
> > +
> > +static void pop_split_desc(struct vhost_virtqueue *vq)
> > +{
> > + BUG_ON(!vq->ndescs);
> > + --vq->ndescs;
> > +}
> > +
> > +#define VHOST_DESC_FLAGS (VRING_DESC_F_INDIRECT | VRING_DESC_F_WRITE | \
> > + VRING_DESC_F_NEXT)
> > +static int push_split_desc(struct vhost_virtqueue *vq, struct vring_desc
> > *desc, u16 id)
> > +{
> > + struct vhost_desc *h;
> > +
> > + if (unlikely(vq->ndescs >= vq->max_descs))
> > + return -EINVAL;
> > + h = &vq->descs[vq->ndescs++];
> > + h->addr = vhost64_to_cpu(vq, desc->addr);
> > + h->len = vhost32_to_cpu(vq, desc->len);
> > + h->flags = vhost16_to_cpu(vq, desc->flags) & VHOST_DESC_FLAGS;
> > + h->id = id;
> > +
> > + return 0;
> > +}
> > +
> > +static int fetch_indirect_descs(struct vhost_virtqueue *vq,
> > + struct vhost_desc *indirect,
> > + u16 head)
> > +{
> > + struct vring_desc desc;
> > + unsigned int i = 0, count, found = 0;
> > + u32 len = 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, indirect->addr, len, vq->indirect,
> > + UIO_MAXIOV, VHOST_ACCESS_RO);
> > + if (unlikely(ret < 0)) {
> > + if (ret != -EAGAIN)
> > + 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;
> > + }
> > + if (unlikely(vq->ndescs + count > vq->max_descs)) {
> > + vq_err(vq, "Too many indirect + direct descs: %d + %d\n",
> > + vq->ndescs, indirect->len);
> > + return -E2BIG;
> > + }
> > +
> > + do {
> > + 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_full(&desc, sizeof(desc), &from)))
> > {
> > + vq_err(vq, "Failed indirect descriptor: idx %d, %zx\n",
> > + i, (size_t)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)indirect->addr + i * sizeof desc);
> > + return -EINVAL;
> > + }
> > +
> > + push_split_desc(vq, &desc, head);
>
>
> The error is ignored.
See above:
if (unlikely(vq->ndescs + count > vq->max_descs))
So it can't fail here, we never fetch unless there's space.
I guess we can add a WARN_ON here.
>
> > + } while ((i = next_desc(vq, &desc)) != -1);
> > + return 0;
> > +}
> > +
> > +static int fetch_descs(struct vhost_virtqueue *vq)
> > +{
> > + unsigned int i, head, found = 0;
> > + struct vhost_desc *last;
> > + struct vring_desc desc;
> > + __virtio16 avail_idx;
> > + __virtio16 ring_head;
> > + u16 last_avail_idx;
> > + int ret;
> > +
> > + /* Check it isn't doing very strange things with descriptor numbers. */
> > + last_avail_idx = vq->last_avail_idx;
> > +
> > + if (vq->avail_idx == vq->last_avail_idx) {
> > + if (unlikely(vhost_get_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 */
> > + if (unlikely(vhost_get_avail_head(vq, &ring_head, last_avail_idx))) {
> > + 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;
> > + }
> > +
> > + i = head;
> > + do {
> > + 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 = vhost_get_desc(vq, &desc, i);
> > + if (unlikely(ret)) {
> > + vq_err(vq, "Failed to get descriptor: idx %d addr %p\n",
> > + i, vq->desc + i);
> > + return -EFAULT;
> > + }
> > + ret = push_split_desc(vq, &desc, head);
> > + if (unlikely(ret)) {
> > + vq_err(vq, "Failed to save descriptor: idx %d\n", i);
> > + return -EINVAL;
> > + }
> > + } while ((i = next_desc(vq, &desc)) != -1);
> > +
> > + last = peek_split_desc(vq);
> > + if (unlikely(last->flags & VRING_DESC_F_INDIRECT)) {
> > + pop_split_desc(vq);
> > + ret = fetch_indirect_descs(vq, last, head);
>
>
> Note that this means we don't supported chained indirect descriptors which
> complies the spec but we support this in vhost_get_vq_desc().
Well the spec says:
A driver MUST NOT set both VIRTQ_DESC_F_INDIRECT and VIRTQ_DESC_F_NEXT
in flags.
Did I miss anything?
> We probably need either fail early or just support that.
>
> Thanks
>
>
> > + if (unlikely(ret < 0)) {
> > + if (ret != -EAGAIN)
> > + vq_err(vq, "Failure detected "
> > + "in indirect descriptor at idx %d\n",
> > head);
> > + return ret;
> > + }
> > + }
> > +
> > + /* 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));
> > +
> > + /* On success, increment avail index. */
> > + vq->last_avail_idx++;
> > +
> > + 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_batch(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)
> > +{
> > + int ret = fetch_descs(vq);
> > + int i;
> > +
> > + if (ret)
> > + return ret;
> > +
> > + /* Now convert to IOV */
> > + /* When we start there are none of either input nor output. */
> > + *out_num = *in_num = 0;
> > + if (unlikely(log))
> > + *log_num = 0;
> > +
> > + for (i = 0; i < vq->ndescs; ++i) {
> > + unsigned iov_count = *in_num + *out_num;
> > + struct vhost_desc *desc = &vq->descs[i];
> > + int access;
> > +
> > + if (desc->flags & ~VHOST_DESC_FLAGS) {
> > + vq_err(vq, "Unexpected flags: 0x%x at descriptor id
> > 0x%x\n",
> > + desc->flags, desc->id);
> > + ret = -EINVAL;
> > + goto err;
> > + }
> > + if (desc->flags & VRING_DESC_F_WRITE)
> > + access = VHOST_ACCESS_WO;
> > + else
> > + access = VHOST_ACCESS_RO;
> > + ret = translate_desc(vq, desc->addr,
> > + desc->len, iov + iov_count,
> > + iov_size - iov_count, access);
> > + if (unlikely(ret < 0)) {
> > + if (ret != -EAGAIN)
> > + vq_err(vq, "Translation failure %d descriptor
> > idx %d\n",
> > + ret, i);
> > + goto err;
> > + }
> > + if (access == VHOST_ACCESS_WO) {
> > + /* If this is an input descriptor,
> > + * increment that count. */
> > + *in_num += ret;
> > + if (unlikely(log && ret)) {
> > + log[*log_num].addr = desc->addr;
> > + log[*log_num].len = 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);
> > + ret = -EINVAL;
> > + goto err;
> > + }
> > + *out_num += ret;
> > + }
> > +
> > + ret = desc->id;
> > + }
> > +
> > + vq->ndescs = 0;
> > +
> > + return ret;
> > +
> > +err:
> > + vhost_discard_vq_desc(vq, 1);
> > + vq->ndescs = 0;
> > +
> > + return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(vhost_get_vq_desc_batch);
> > +
> > /* Reverse the effect of vhost_get_vq_desc. Useful for error handling. */
> > void vhost_discard_vq_desc(struct vhost_virtqueue *vq, int n)
> > {
> > diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> > index 60cab4c78229..0976a2853935 100644
> > --- a/drivers/vhost/vhost.h
> > +++ b/drivers/vhost/vhost.h
> > @@ -60,6 +60,13 @@ enum vhost_uaddr_type {
> > VHOST_NUM_ADDRS = 3,
> > };
> > +struct vhost_desc {
> > + u64 addr;
> > + u32 len;
> > + u16 flags; /* VRING_DESC_F_WRITE, VRING_DESC_F_NEXT */
> > + u16 id;
> > +};
> > +
> > /* The virtqueue structure describes a queue attached to a device. */
> > struct vhost_virtqueue {
> > struct vhost_dev *dev;
> > @@ -71,6 +78,11 @@ struct vhost_virtqueue {
> > vring_avail_t __user *avail;
> > vring_used_t __user *used;
> > const struct vhost_iotlb_map *meta_iotlb[VHOST_NUM_ADDRS];
> > +
> > + struct vhost_desc *descs;
> > + int ndescs;
> > + int max_descs;
> > +
> > struct file *kick;
> > struct eventfd_ctx *call_ctx;
> > struct eventfd_ctx *error_ctx;
> > @@ -175,6 +187,10 @@ long vhost_vring_ioctl(struct vhost_dev *d, unsigned
> > int ioctl, void __user *arg
> > bool vhost_vq_access_ok(struct vhost_virtqueue *vq);
> > bool vhost_log_access_ok(struct vhost_dev *);
> > +int vhost_get_vq_desc_batch(struct vhost_virtqueue *,
> > + struct iovec iov[], unsigned int iov_count,
> > + unsigned int *out_num, unsigned int *in_num,
> > + struct vhost_log *log, unsigned int *log_num);
> > int vhost_get_vq_desc(struct vhost_virtqueue *,
> > struct iovec iov[], unsigned int iov_count,
> > unsigned int *out_num, unsigned int *in_num,
