Re: [PATCH] vhost-vdpa: fail enabling virtqueue in certain conditions

[Jason Wang]

On Tue, Feb 6, 2024 at 10:52 PM Stefano Garzarella <sgarzare@redhatcom> wrote:
>
> If VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK is not negotiated, we expect
> the driver to enable virtqueue before setting DRIVER_OK. If the driver
> tries anyway, better to fail right away as soon as we get the ioctl.
> Let's also update the documentation to make it clearer.
>
> We had a problem in QEMU for not meeting this requirement, see
> https://lore.kernel.org/qemu-devel/20240202132521.32714-1-kwolf@xxxxxxxxxx/

Maybe it's better to only enable cvq when the backend supports
VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK. Eugenio, any comment on this?

>
> Fixes: 9f09fd6171fe ("vdpa: accept VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK backend feature")
> Cc: eperezma@xxxxxxxxxx
> Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> ---
>  include/uapi/linux/vhost_types.h | 3 ++-
>  drivers/vhost/vdpa.c             | 4 ++++
>  2 files changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/vhost_types.h b/include/uapi/linux/vhost_types.h
> index d7656908f730..5df49b6021a7 100644
> --- a/include/uapi/linux/vhost_types.h
> +++ b/include/uapi/linux/vhost_types.h
> @@ -182,7 +182,8 @@ struct vhost_vdpa_iova_range {
>  /* Device can be resumed */
>  #define VHOST_BACKEND_F_RESUME  0x5
>  /* Device supports the driver enabling virtqueues both before and after
> - * DRIVER_OK
> + * DRIVER_OK. If this feature is not negotiated, the virtqueues must be
> + * enabled before setting DRIVER_OK.
>   */
>  #define VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK  0x6
>  /* Device may expose the virtqueue's descriptor area, driver area and
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index bc4a51e4638b..1fba305ba8c1 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -651,6 +651,10 @@ static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
>         case VHOST_VDPA_SET_VRING_ENABLE:
>                 if (copy_from_user(&s, argp, sizeof(s)))
>                         return -EFAULT;
> +               if (!vhost_backend_has_feature(vq,
> +                       VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK) &&
> +                   (ops->get_status(vdpa) & VIRTIO_CONFIG_S_DRIVER_OK))
> +                       return -EINVAL;

As discussed, without VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK, we don't
know if parents can do vq_ready after driver_ok.

So maybe we need to keep this behaviour to unbreak some "legacy" userspace?

For example ifcvf did:

static void ifcvf_vdpa_set_vq_ready(struct vdpa_device *vdpa_dev,
                                    u16 qid, bool ready)
{
  struct ifcvf_hw *vf = vdpa_to_vf(vdpa_dev);

        ifcvf_set_vq_ready(vf, qid, ready);
}

And it did:

void ifcvf_set_vq_ready(struct ifcvf_hw *hw, u16 qid, bool ready)
{
        struct virtio_pci_common_cfg __iomem *cfg = hw->common_cfg;

        vp_iowrite16(qid, &cfg->queue_select);
        vp_iowrite16(ready, &cfg->queue_enable);
}

Though it didn't advertise VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK?

Adding LingShan for more thought.

Thanks

>                 ops->set_vq_ready(vdpa, idx, s.num);
>                 return 0;
>         case VHOST_VDPA_GET_VRING_GROUP:
> --
> 2.43.0
>