Re: [PATCH v13 05/13] vdpa: Add reset callback in vdpa_config_ops

[Yongji Xie <xieyongji@bytedance.com>]

On Mon, Sep 6, 2021 at 1:56 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Tue, Aug 31, 2021 at 06:36:26PM +0800, Xie Yongji wrote:
> > This adds a new callback to support device specific reset
> > behavior. The vdpa bus driver will call the reset function
> > instead of setting status to zero during resetting.
> >
> > Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
>
>
> This does gloss over a significant change though:
>
>
> > ---
> > @@ -348,12 +352,12 @@ static inline struct device *vdpa_get_dma_dev(struct vdpa_device *vdev)
> >       return vdev->dma_dev;
> >  }
> >
> > -static inline void vdpa_reset(struct vdpa_device *vdev)
> > +static inline int vdpa_reset(struct vdpa_device *vdev)
> >  {
> >       const struct vdpa_config_ops *ops = vdev->config;
> >
> >       vdev->features_valid = false;
> > -     ops->set_status(vdev, 0);
> > +     return ops->reset(vdev);
> >  }
> >
> >  static inline int vdpa_set_features(struct vdpa_device *vdev, u64 features)
>
>
> Unfortunately this breaks virtio_vdpa:
>
>
> static void virtio_vdpa_reset(struct virtio_device *vdev)
> {
>         struct vdpa_device *vdpa = vd_get_vdpa(vdev);
>
>         vdpa_reset(vdpa);
> }
>
>
> and there's no easy way to fix this, kernel can't recover
> from a reset failure e.g. during driver unbind.
>

Yes, but it should be safe with the protection of software IOTLB even
if the reset() fails during driver unbind.

Thanks,
Yongji