On Fri, Apr 09, 2021 at 12:47:55PM +0800, Jason Wang
wrote:>
> ? 2021/4/8 ??11:59, Michael S. Tsirkin ??:
> > 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 at redhat.com>
> > 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 ...
My point is this neither fixes or prevents this.
So my suggestion is to finally add ioctls along the lines
of PROTOCOL_FEATURES of vhost-user.
Then that one can have bits for legacy le, legacy be and modern.
BTW I looked at vhost-user and it does not look like that
has a solution for this problem either, right?
>
> > 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
I frankly think we'll need PROTOCOL_FEATURES anyway, it's too useful ...
so why not teach drivers about it and be done with it? You can't emulate
legacy on modern in a cross endian situation because of vring
endian-ness ...
>
> >
> >
> >
> >
> >
> > > ---
> > > 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