On Thu, Dec 5, 2024 at 9:35 PM Sahil Siddiq <icegambi...@gmail.com> wrote:
>
> This commit is the first in a series to add support for packed
> virtqueues in vhost_shadow_virtqueue.
>
> This patch implements the insertion of available buffers in the
> descriptor area. It takes into account descriptor chains, but does
> not consider indirect descriptors.
>
> Also validate svq-specific features that vdpa supports.
>
> Signed-off-by: Sahil Siddiq <sahil...@proton.me>
> ---
> Changes v3 -> v4:
> - Split commit #1 in v3 into 2 commits.
> - vhost-shadow-virtqueue.c
> (vhost_svq_valid_features): Add enums.
>
> hw/virtio/vhost-shadow-virtqueue.c | 83 +++++++++++++++++++++++++++++-
> 1 file changed, 81 insertions(+), 2 deletions(-)
>
> diff --git a/hw/virtio/vhost-shadow-virtqueue.c
> b/hw/virtio/vhost-shadow-virtqueue.c
> index bb7cf6d5db..6eee01ab3c 100644
> --- a/hw/virtio/vhost-shadow-virtqueue.c
> +++ b/hw/virtio/vhost-shadow-virtqueue.c
> @@ -33,6 +33,9 @@ bool vhost_svq_valid_features(uint64_t features, Error
> **errp)
> ++b) {
> switch (b) {
> case VIRTIO_F_ANY_LAYOUT:
> + case VIRTIO_F_RING_PACKED:
> + case VIRTIO_F_RING_RESET:
> + case VIRTIO_RING_F_INDIRECT_DESC:
> case VIRTIO_RING_F_EVENT_IDX:
This is good, but it should be added in the last commit. Otherwise
we're enabling packed vq without the code to handle it.
The rest looks good to me.
> continue;
>
> @@ -178,7 +181,78 @@ static void vhost_svq_add_split(VhostShadowVirtqueue
> *svq,
> /* Update the avail index after write the descriptor */
> smp_wmb();
> avail->idx = cpu_to_le16(svq->shadow_avail_idx);
> +}
>
> +/**
> + * Write descriptors to SVQ packed vring
> + *
> + * @svq: The shadow virtqueue
> + * @out_sg: The iovec to the guest
> + * @out_num: Outgoing iovec length
> + * @in_sg: The iovec from the guest
> + * @in_num: Incoming iovec length
> + * @sgs: Cache for hwaddr
> + * @head: Saves current free_head
> + */
> +static void vhost_svq_add_packed(VhostShadowVirtqueue *svq,
> + const struct iovec *out_sg, size_t out_num,
> + const struct iovec *in_sg, size_t in_num,
> + hwaddr *sgs, unsigned *head)
> +{
> + uint16_t id, curr, i, head_flags = 0;
> + size_t num = out_num + in_num;
> + unsigned n;
> +
> + struct vring_packed_desc *descs = svq->vring_packed.vring.desc;
> +
> + *head = svq->vring_packed.next_avail_idx;
> + i = *head;
> + id = svq->free_head;
> + curr = id;
> +
> + /* Write descriptors to SVQ packed vring */
> + for (n = 0; n < num; n++) {
> + uint16_t flags = cpu_to_le16(svq->vring_packed.avail_used_flags |
> + (n < out_num ? 0 : VRING_DESC_F_WRITE) |
> + (n + 1 == num ? 0 : VRING_DESC_F_NEXT));
> + if (i == *head) {
> + head_flags = flags;
> + } else {
> + descs[i].flags = flags;
> + }
> +
> + descs[i].addr = cpu_to_le64(sgs[n]);
> + descs[i].id = id;
> + if (n < out_num) {
> + descs[i].len = cpu_to_le32(out_sg[n].iov_len);
> + } else {
> + descs[i].len = cpu_to_le32(in_sg[n - out_num].iov_len);
> + }
> +
> + curr = cpu_to_le16(svq->desc_next[curr]);
> +
> + if (++i >= svq->vring_packed.vring.num) {
> + i = 0;
> + svq->vring_packed.avail_used_flags ^=
> + 1 << VRING_PACKED_DESC_F_AVAIL |
> + 1 << VRING_PACKED_DESC_F_USED;
> + }
> + }
> +
> + if (i <= *head) {
> + svq->vring_packed.avail_wrap_counter ^= 1;
> + }
> +
> + svq->vring_packed.next_avail_idx = i;
> + svq->free_head = curr;
> +
> + /*
> + * A driver MUST NOT make the first descriptor in the list
> + * available before all subsequent descriptors comprising
> + * the list are made available.
> + */
> + smp_wmb();
> + svq->vring_packed.vring.desc[*head].flags = head_flags;
> }
>
> static void vhost_svq_kick(VhostShadowVirtqueue *svq)
> @@ -240,8 +314,13 @@ int vhost_svq_add(VhostShadowVirtqueue *svq, const
> struct iovec *out_sg,
> return -EINVAL;
> }
>
> - vhost_svq_add_split(svq, out_sg, out_num, in_sg,
> - in_num, sgs, &qemu_head);
> + if (virtio_vdev_has_feature(svq->vdev, VIRTIO_F_RING_PACKED)) {
> + vhost_svq_add_packed(svq, out_sg, out_num, in_sg,
> + in_num, sgs, &qemu_head);
> + } else {
> + vhost_svq_add_split(svq, out_sg, out_num, in_sg,
> + in_num, sgs, &qemu_head);
> + }
>
> svq->num_free -= ndescs;
> svq->desc_state[qemu_head].elem = elem;
> --
> 2.47.0
>
