? 2022/7/21 16:43, Guo Zhi ??:> If in order feature negotiated, we can skip the used ring to get
> buffer's desc id sequentially.
Let's rename the patch to something like "in order support for
virtio_ring"
>
> Signed-off-by: Guo Zhi <qtxuning1999 at sjtu.edu.cn>
> ---
> drivers/virtio/virtio_ring.c | 37 ++++++++++++++++++++++++++++--------
> 1 file changed, 29 insertions(+), 8 deletions(-)
I don't see packed support in this patch, we need to implement that.
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index a5ec724c0..4d57a4edc 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -144,6 +144,9 @@ struct vring_virtqueue {
> /* DMA address and size information */
> dma_addr_t queue_dma_addr;
> size_t queue_size_in_bytes;
> +
> + /* In order feature batch begin here */
> + u16 next_batch_desc_begin;
> } split;
>
> /* Available for packed ring */
> @@ -700,8 +703,10 @@ static void detach_buf_split(struct vring_virtqueue
*vq, unsigned int head,
> }
>
> vring_unmap_one_split(vq, i);
> - vq->split.desc_extra[i].next = vq->free_head;
> - vq->free_head = head;
> + if (!virtio_has_feature(vq->vq.vdev, VIRTIO_F_IN_ORDER)) {
> + vq->split.desc_extra[i].next = vq->free_head;
> + vq->free_head = head;
> + }
Let's add a comment to explain why we don't need anything if in order is
neogitated.
>
> /* Plus final descriptor */
> vq->vq.num_free++;
> @@ -743,7 +748,8 @@ static void *virtqueue_get_buf_ctx_split(struct
virtqueue *_vq,
> {
> struct vring_virtqueue *vq = to_vvq(_vq);
> void *ret;
> - unsigned int i;
> + __virtio16 nextflag = cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_NEXT);
> + unsigned int i, j;
> u16 last_used;
>
> START_USE(vq);
> @@ -762,11 +768,24 @@ static void *virtqueue_get_buf_ctx_split(struct
virtqueue *_vq,
> /* Only get used array entries after they have been exposed by host. */
> virtio_rmb(vq->weak_barriers);
>
> - last_used = (vq->last_used_idx & (vq->split.vring.num - 1));
> - i = virtio32_to_cpu(_vq->vdev,
> - vq->split.vring.used->ring[last_used].id);
> - *len = virtio32_to_cpu(_vq->vdev,
> - vq->split.vring.used->ring[last_used].len);
> + if (virtio_has_feature(_vq->vdev, VIRTIO_F_IN_ORDER)) {
> + /* Skip used ring and get used desc in order*/
> + i = vq->split.next_batch_desc_begin;
> + j = i;
> + while (vq->split.vring.desc[j].flags & nextflag)
Let's don't depend on the descriptor ring which is under the control of
the malicious hypervisor.
Let's use desc_extra that is not visible by the hypervisor. More can be
seen in this commit:
72b5e8958738 ("virtio-ring: store DMA metadata in desc_extra for split
virtqueue")
> + j = (j + 1) % vq->split.vring.num;
> + /* move to next */
> + j = (j + 1) % vq->split.vring.num;
> + vq->split.next_batch_desc_begin = j;
I'm not sure I get the logic here, basically I think we should check
buffer instead of descriptor here.
So if vring.used->ring[last_used].id != last_used, we know all
[last_used, vring.used->ring[last_used].id] have been used in a batch?
> +
> + /* TODO: len of buffer */
So spec said:
"
The skipped buffers (for which no used ring entry was written) are
assumed to have been used (read or written) by the device completely.
"
Thanks
> + } else {
> + last_used = (vq->last_used_idx & (vq->split.vring.num - 1));
> + i = virtio32_to_cpu(_vq->vdev,
> + vq->split.vring.used->ring[last_used].id);
> + *len = virtio32_to_cpu(_vq->vdev,
> + vq->split.vring.used->ring[last_used].len);
> + }
>
> if (unlikely(i >= vq->split.vring.num)) {
> BAD_RING(vq, "id %u out of range\n", i);
> @@ -2234,6 +2253,8 @@ struct virtqueue *__vring_new_virtqueue(unsigned int
index,
> vq->split.avail_flags_shadow = 0;
> vq->split.avail_idx_shadow = 0;
>
> + vq->split.next_batch_desc_begin = 0;
> +
> /* No callback? Tell other side not to bother us. */
> if (!callback) {
> vq->split.avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT;