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@xxxxxxxxxxx>
---
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;
