Re: [RFC PATCH] vdpa: mandate 1.0 device

[Jason Wang]

在 2021/4/8 下午11:59, Michael S. Tsirkin 写道:
> On Thu, Apr 08, 2021 at 04:26:48PM +0800, Jason Wang wrote:
> > This patch mandates 1.0 for vDPA devices. The goal is to have the
> > semantic of normative statement in the virtio spec and eliminate the
> > burden of transitional device for both vDPA bus and vDPA parent.
> >
> > uAPI seems fine since all the vDPA parent mandates
> > VIRTIO_F_ACCESS_PLATFORM which implies 1.0 devices.
> >
> > For legacy guests, it can still work since Qemu will mediate when
> > necessary (e.g doing the endian conversion).
> >
> > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> Hmm. If we do this, don't we still have a problem with
> legacy drivers which don't ack 1.0?


Yes, but it's not something that is introduced in this commit. The 
legacy driver never work ...


> Note 1.0 affects ring endianness which is not mediated in QEMU
> so QEMU can't pretend to device guest is 1.0.


Right, I plan to send patches to do mediation in the Qemu to unbreak 
legacy drivers.

Thanks


> > ---
> >   include/linux/vdpa.h | 6 ++++++
> >   1 file changed, 6 insertions(+)
> >
> > diff --git a/include/linux/vdpa.h b/include/linux/vdpa.h
> > index 0fefeb976877..cfde4ec999b4 100644
> > --- a/include/linux/vdpa.h
> > +++ b/include/linux/vdpa.h
> > @@ -6,6 +6,7 @@
> >   #include <linux/device.h>
> >   #include <linux/interrupt.h>
> >   #include <linux/vhost_iotlb.h>
> > +#include <uapi/linux/virtio_config.h>
> >   
> >   /**
> >    * vDPA callback definition.
> > @@ -317,6 +318,11 @@ static inline int vdpa_set_features(struct vdpa_device *vdev, u64 features)
> >   {
> >           const struct vdpa_config_ops *ops = vdev->config;
> >   
> > +        /* Mandating 1.0 to have semantics of normative statements in
> > +         * the spec. */
> > +        if (!(features & BIT_ULL(VIRTIO_F_VERSION_1)))
> > +		return -EINVAL;
> > +
> >   	vdev->features_valid = true;
> >           return ops->set_features(vdev, features);
> >   }
> > --
> > 2.25.1