On Mon, Mar 24, 2025 at 3:00 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.
>
> Linux commit 1225c216d954 ("vp_vdpa: allow set vq state to initial
> state after reset") enabled the vp_vdpa driver to set the vq state to
> the device's initial state. This works differently for split and packed
> vqs.
>
> With shadow virtqueues enabled, vhost-vdpa sets the vring base using
> the VHOST_SET_VRING_BASE ioctl. The payload (vhost_vring_state)
> differs for split and packed vqs. The implementation in QEMU currently
> uses the payload required for split vqs (i.e., the num field of
> vhost_vring_state is set to 0). The kernel throws EOPNOTSUPP when this
> payload is used with packed vqs.
>
> This patch sets the num field in the payload appropriately so vhost-vdpa
> (with the vp_vdpa driver) can use packed SVQs.
>
> Link: https://lists.nongnu.org/archive/html/qemu-devel/2024-10/msg05106.html
> Link: https://lore.kernel.org/r/20210602021536.39525-4-jasow...@redhat.com
> Link: 1225c216d954 ("vp_vdpa: allow set vq state to initial state after
> reset")
> Signed-off-by: Sahil Siddiq <sahil...@proton.me>
> Acked-by: Eugenio Pérez <epere...@redhat.com>
> ---
> Changes from v4 -> v5:
> - Initially commit #5 in v4.
> - Fix coding style of commit block as stated by checkpatch.pl.
>
> hw/virtio/vhost-vdpa.c | 15 +++++++++++++++
> 1 file changed, 15 insertions(+)
>
> diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> index 58c8931d89..0625e349b3 100644
> --- a/hw/virtio/vhost-vdpa.c
> +++ b/hw/virtio/vhost-vdpa.c
> @@ -1265,6 +1265,21 @@ static bool vhost_vdpa_svq_setup(struct vhost_dev *dev,
> };
> int r;
>
> + /*
> + * In Linux, the upper 16 bits of s.num is encoded as
> + * the last used idx while the lower 16 bits is encoded
> + * as the last avail idx when using packed vqs. The most
> + * significant bit for each idx represents the counter
> + * and should be set in both cases while the remaining
> + * bits are cleared.
> + */
> + if (virtio_vdev_has_feature(dev->vdev, VIRTIO_F_RING_PACKED)) {
> + uint32_t last_avail_idx = 0 | (1 << VRING_PACKED_EVENT_F_WRAP_CTR);
> + uint32_t last_used_idx = 0 | (1 << VRING_PACKED_EVENT_F_WRAP_CTR);
> +
> + s.num = (last_used_idx << 16) | last_avail_idx;
> + }
> +
This should be added before 6/7 so we don't declare we support packed
without this.
> r = vhost_vdpa_set_dev_vring_base(dev, &s);
> if (unlikely(r)) {
> error_setg_errno(errp, -r, "Cannot set vring base");
> --
> 2.48.1
>
