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 <mst@xxxxxxxxxx> > > Signed-off-by: Eugenio Pérez <eperezma@xxxxxxxxxx> > > Link: https://lore.kernel.org/r/20200401183118.8334-2-eperezma@xxxxxxxxxx > > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx> > > --- > > 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,
