Messages in this thread | | | Subject | Re: [PATCH RFC 01/13] vhost: option to fetch descriptors through an independent struct | From | Jason Wang <> | Date | Wed, 3 Jun 2020 20:04:45 +0800 |
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On 2020/6/3 下午5:48, Michael S. Tsirkin wrote: > 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:
[...]
>>> + >>> +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.
Yes.
> >>> + } 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? >
No, but I meant current vhost_get_vq_desc() supports chained indirect descriptor. Not sure if there's an application that depends on this silently.
Thanks
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