Messages in this thread | | | Date | Tue, 26 Jul 2022 16:07:46 +0800 | Subject | Re: [RFC 4/5] virtio: get desc id in order | From | Jason Wang <> |
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在 2022/7/21 16:43, Guo Zhi 写道: > 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@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;
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