On Mon, May 6, 2024 at 5:06 PM Jonah Palmer <jonah.pal...@oracle.com> wrote:
>
> Add VIRTIO_F_IN_ORDER feature support for virtqueue_flush operations.
>
> The goal of the virtqueue_flush operation when the VIRTIO_F_IN_ORDER
> feature has been negotiated is to write elements to the used/descriptor
> ring in-order and then update used_idx.
>
> The function iterates through the VirtQueueElement used_elems array
> in-order starting at vq->used_idx. If the element is valid (filled), the
> element is written to the used/descriptor ring. This process continues
> until we find an invalid (not filled) element.
>
> If any elements were written, the used_idx is updated.
>
> Tested-by: Lei Yang <leiy...@redhat.com>
> Signed-off-by: Jonah Palmer <jonah.pal...@oracle.com>
> ---
> hw/virtio/virtio.c | 75 +++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 74 insertions(+), 1 deletion(-)
>
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 064046b5e2..0efed2c88e 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -1006,6 +1006,77 @@ static void virtqueue_packed_flush(VirtQueue *vq,
> unsigned int count)
> }
> }
>
> +static void virtqueue_ordered_flush(VirtQueue *vq)
> +{
> + unsigned int i = vq->used_idx;
> + unsigned int ndescs = 0;
> + uint16_t old = vq->used_idx;
> + bool packed;
> + VRingUsedElem uelem;
> +
> + packed = virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED);
> +
> + if (packed) {
> + if (unlikely(!vq->vring.desc)) {
> + return;
> + }
> + } else if (unlikely(!vq->vring.used)) {
> + return;
> + }
> +
> + /* First expected in-order element isn't ready, nothing to do */
> + if (!vq->used_elems[i].filled) {
> + return;
> + }
> +
> + /* Write first expected in-order element to used ring (split VQs) */
> + if (!packed) {
> + uelem.id = vq->used_elems[i].index;
> + uelem.len = vq->used_elems[i].len;
> + vring_used_write(vq, &uelem, i);
> + }
> +
> + ndescs += vq->used_elems[i].ndescs;
> + i += ndescs;
> + if (i >= vq->vring.num) {
> + i -= vq->vring.num;
> + }
> +
> + /* Search for more filled elements in-order */
> + while (vq->used_elems[i].filled) {
> + if (packed) {
> + virtqueue_packed_fill_desc(vq, &vq->used_elems[i], ndescs,
> false);
> + } else {
> + uelem.id = vq->used_elems[i].index;
> + uelem.len = vq->used_elems[i].len;
> + vring_used_write(vq, &uelem, i);
> + }
> +
> + vq->used_elems[i].filled = false;
> + ndescs += vq->used_elems[i].ndescs;
> + i += ndescs;
> + if (i >= vq->vring.num) {
> + i -= vq->vring.num;
> + }
> + }
> +
I may be missing something, but you have split out the first case as a
special one, totally out of the while loop. Can't it be contained in
the loop checking !(packed && i == vq->used_idx)? That would avoid
code duplication.
A comment can be added in the line of "first entry of packed is
written the last so the guest does not see invalid descriptors".
> + if (packed) {
> + virtqueue_packed_fill_desc(vq, &vq->used_elems[vq->used_idx], 0,
> true);
> + vq->used_idx += ndescs;
> + if (vq->used_idx >= vq->vring.num) {
> + vq->used_idx -= vq->vring.num;
> + vq->used_wrap_counter ^= 1;
> + vq->signalled_used_valid = false;
> + }
> + } else {
> + vring_used_idx_set(vq, i);
> + if (unlikely((int16_t)(i - vq->signalled_used) < (uint16_t)(i -
> old))) {
> + vq->signalled_used_valid = false;
> + }
> + }
> + vq->inuse -= ndescs;
> +}
> +
> void virtqueue_flush(VirtQueue *vq, unsigned int count)
> {
> if (virtio_device_disabled(vq->vdev)) {
> @@ -1013,7 +1084,9 @@ void virtqueue_flush(VirtQueue *vq, unsigned int count)
> return;
> }
>
> - if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) {
> + if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_IN_ORDER)) {
> + virtqueue_ordered_flush(vq);
> + } else if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) {
> virtqueue_packed_flush(vq, count);
> } else {
> virtqueue_split_flush(vq, count);
> --
> 2.39.3
>
