On Mon, Mar 24, 2025 at 3:00 PM Sahil Siddiq <icegambi...@gmail.com> wrote:
>
> Implement the insertion of available buffers in the descriptor area of
> packed shadow virtqueues. It takes into account descriptor chains, but
> does not consider indirect descriptors.
>
> Enable the packed SVQ to forward the descriptors to the device.
>
> Signed-off-by: Sahil Siddiq <sahil...@proton.me>
> ---
> Changes from v4 -> v5:
> - This was commit #2 in v4. This has been reordered to commit #3
> based on review comments.
> - vhost-shadow-virtqueue.c:
> (vhost_svq_valid_features): Move addition of enums to commit #6
> based on review comments.
> (vhost_svq_add_packed): Set head_idx to buffer id instead of vring's
> index.
> (vhost_svq_kick): Split into vhost_svq_kick_split and
> vhost_svq_kick_packed.
> (vhost_svq_add): Use new vhost_svq_kick_* functions.
>
> hw/virtio/vhost-shadow-virtqueue.c | 117 +++++++++++++++++++++++++++--
> 1 file changed, 112 insertions(+), 5 deletions(-)
>
> diff --git a/hw/virtio/vhost-shadow-virtqueue.c
> b/hw/virtio/vhost-shadow-virtqueue.c
> index 4f74ad402a..6e16cd4bdf 100644
> --- a/hw/virtio/vhost-shadow-virtqueue.c
> +++ b/hw/virtio/vhost-shadow-virtqueue.c
> @@ -193,10 +193,83 @@ 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, head_idx;
> + size_t num = out_num + in_num;
> + unsigned n;
> +
> + struct vring_packed_desc *descs = svq->vring_packed.vring.desc;
> +
> + head_idx = svq->vring_packed.next_avail_idx;
> + i = head_idx;
> + id = svq->free_head;
> + curr = id;
> + *head = 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_idx) {
> + 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_idx) {
> + svq->vring_packed.avail_wrap_counter ^= 1;
> + }
> +
> + svq->vring_packed.next_avail_idx = i;
> + svq->shadow_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_idx].flags = head_flags;
> }
>
> -static void vhost_svq_kick(VhostShadowVirtqueue *svq)
> +static void vhost_svq_kick_split(VhostShadowVirtqueue *svq)
> {
> bool needs_kick;
>
> @@ -209,7 +282,8 @@ static void vhost_svq_kick(VhostShadowVirtqueue *svq)
> if (virtio_vdev_has_feature(svq->vdev, VIRTIO_RING_F_EVENT_IDX)) {
> uint16_t avail_event = le16_to_cpu(
> *(uint16_t *)(&svq->vring.used->ring[svq->vring.num]));
> - needs_kick = vring_need_event(avail_event, svq->shadow_avail_idx,
> svq->shadow_avail_idx - 1);
> + needs_kick = vring_need_event(avail_event, svq->shadow_avail_idx,
> + svq->shadow_avail_idx - 1);
> } else {
> needs_kick =
> !(svq->vring.used->flags &
> cpu_to_le16(VRING_USED_F_NO_NOTIFY));
> @@ -222,6 +296,30 @@ static void vhost_svq_kick(VhostShadowVirtqueue *svq)
> event_notifier_set(&svq->hdev_kick);
> }
>
> +static void vhost_svq_kick_packed(VhostShadowVirtqueue *svq)
> +{
> + bool needs_kick;
> +
> + /*
> + * We need to expose the available array entries before checking
> + * notification suppressions.
> + */
> + smp_mb();
> +
> + if (virtio_vdev_has_feature(svq->vdev, VIRTIO_RING_F_EVENT_IDX)) {
> + return;
It's weird SVQ does not need to kick if _F_EVENT_IDX. This should have
code checking the device ring flags etc.
> + } else {
> + needs_kick = (svq->vring_packed.vring.device->flags !=
> + cpu_to_le16(VRING_PACKED_EVENT_FLAG_DISABLE));
> + }
> +
> + if (!needs_kick) {
> + return;
> + }
> +
> + event_notifier_set(&svq->hdev_kick);
> +}
> +
> /**
> * Add an element to a SVQ.
> *
> @@ -258,13 +356,22 @@ 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 (svq->is_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;
> svq->desc_state[qemu_head].ndescs = ndescs;
> - vhost_svq_kick(svq);
> + if (svq->is_packed) {
> + vhost_svq_kick_packed(svq);
> + } else {
> + vhost_svq_kick_split(svq);
> + }
> return 0;
> }
>
> --
> 2.48.1
>
