On Fri, Jul 26, 2024 at 11:58 AM Sahil Siddiq <icegambi...@gmail.com> wrote:
>
> This is the first patch 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.
>
> Signed-off-by: Sahil Siddiq <sahil...@proton.me>
> ---
> Changes v1 -> v2:
> * Split commit from RFC v1 into two commits.
> * vhost-shadow-virtqueue.c
> (vhost_svq_add_packed):
> - Merge with "vhost_svq_vring_write_descs_packed()"
> - Remove "num == 0" check
>
> hw/virtio/vhost-shadow-virtqueue.c | 93 +++++++++++++++++++++++++++++-
> 1 file changed, 92 insertions(+), 1 deletion(-)
>
> diff --git a/hw/virtio/vhost-shadow-virtqueue.c
> b/hw/virtio/vhost-shadow-virtqueue.c
> index fc5f408f77..c7b7e0c477 100644
> --- a/hw/virtio/vhost-shadow-virtqueue.c
> +++ b/hw/virtio/vhost-shadow-virtqueue.c
> @@ -217,6 +217,91 @@ static bool vhost_svq_add_split(VhostShadowVirtqueue
> *svq,
> return true;
> }
>
> +static bool vhost_svq_add_packed(VhostShadowVirtqueue *svq,
> + const struct iovec *out_sg, size_t out_num,
> + const struct iovec *in_sg, size_t in_num,
> + unsigned *head)
> +{
> + bool ok;
> + uint16_t head_flags = 0;
> + g_autofree hwaddr *sgs = g_new(hwaddr, out_num + in_num);
> +
> + *head = svq->vring_packed.next_avail_idx;
> +
> + /* We need some descriptors here */
> + if (unlikely(!out_num && !in_num)) {
> + qemu_log_mask(LOG_GUEST_ERROR,
> + "Guest provided element with no descriptors");
> + return false;
> + }
> +
> + uint16_t id, curr, i;
> + unsigned n;
> + struct vring_packed_desc *descs = svq->vring_packed.vring.desc;
> +
> + i = *head;
> + id = svq->free_head;
> + curr = id;
> +
> + size_t num = out_num + in_num;
> +
> + ok = vhost_svq_translate_addr(svq, sgs, out_sg, out_num);
> + if (unlikely(!ok)) {
> + return false;
> + }
> +
> + ok = vhost_svq_translate_addr(svq, sgs + out_num, in_sg, in_num);
> + if (unlikely(!ok)) {
> + return false;
> + }
> +
(sorry I missed this from the RFC v1) I think all of the above should
be in the caller, isn't it? It is duplicated with split.
Also, declarations should be at the beginning of blocks per QEMU
coding style [1].
The rest looks good to me by visual inspection.
> + /* 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;
> +
> + return true;
> +}
> +
> static void vhost_svq_kick(VhostShadowVirtqueue *svq)
> {
> bool needs_kick;
> @@ -258,7 +343,13 @@ int vhost_svq_add(VhostShadowVirtqueue *svq, const
> struct iovec *out_sg,
> return -ENOSPC;
> }
>
> - ok = vhost_svq_add_split(svq, out_sg, out_num, in_sg, in_num,
> &qemu_head);
> + if (virtio_vdev_has_feature(svq->vdev, VIRTIO_F_RING_PACKED)) {
> + ok = vhost_svq_add_packed(svq, out_sg, out_num,
> + in_sg, in_num, &qemu_head);
> + } else {
> + ok = vhost_svq_add_split(svq, out_sg, out_num,
> + in_sg, in_num, &qemu_head);
> + }
> if (unlikely(!ok)) {
> return -EINVAL;
> }
> --
> 2.45.2
>
[1] https://www.qemu.org/docs/master/devel/style.html#declarations
