Messages in this thread | | | Date | Thu, 28 Jul 2022 16:12:39 +0800 | Subject | Re: [RFC 4/5] virtio: get desc id in order | From | Guo Zhi <> |
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On 2022/7/26 16:07, Jason Wang wrote: > > 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. > It will be implemented later. > >> >> 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. > LGTM. > >> /* 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") > LGTM, I will use desc_extra in new version patch. > >> + 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.
Because the vq->last_used_idx != vq->split.vring.used->idx, So the virtio driver know these has at least one used descriptor. the descriptor's id is vq->split.next_batch_desc_begin because of in order. Then we have to traverse the descriptor chain and point vq->split.next_batch_desc_begin to next used descriptor.
Thanks.
> > 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 > The driver will need len in used ring to get buffer size. However in order will not write len of each buffer in used ring. So I will tried pass len of buffer in device header. > >> + } 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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