Re: [PATCH v6 05/10] vdpa: move SVQ vring features check to net/

[Jason Wang <jasowang@redhat.com>]

On Fri, Nov 11, 2022 at 3:56 PM Eugenio Perez Martin
<eperezma@redhat.com> wrote:
>
> On Fri, Nov 11, 2022 at 8:34 AM Jason Wang <jasowang@redhat.com> wrote:
> >
> >
> > 在 2022/11/10 21:09, Eugenio Perez Martin 写道:
> > > On Thu, Nov 10, 2022 at 6:40 AM Jason Wang <jasowang@redhat.com> wrote:
> > >>
> > >> 在 2022/11/9 01:07, Eugenio Pérez 写道:
> > >>> The next patches will start control SVQ if possible. However, we don't
> > >>> know if that will be possible at qemu boot anymore.
> > >>
> > >> If I was not wrong, there's no device specific feature that is checked
> > >> in the function. So it should be general enough to be used by devices
> > >> other than net. Then I don't see any advantage of doing this.
> > >>
> > > Because vhost_vdpa_init_svq is called at qemu boot, failing if it is
> > > not possible to shadow the Virtqueue.
> > >
> > > Now the CVQ will be shadowed if possible, so we need to check this at
> > > device start, not at initialization.
> >
> >
> > Any reason we can't check this at device start? We don't need
> > driver_features and we can do any probing to make sure cvq has an unique
> > group during initialization time.
> >
>
> We need the CVQ index to check if it has an independent group. CVQ
> index depends on the features the guest's ack:
> * If it acks _F_MQ, it is the last one.
> * If it doesn't, CVQ idx is 2.
>
> We cannot have acked features at initialization, and they could
> change: It is valid for a guest to ack _F_MQ, then reset the device,
> then not ack it.

Can we do some probing by negotiating _F_MQ if the device offers it,
then we can know if cvq has a unique group?

>
> >
> > >   To store this information at boot
> > > time is not valid anymore, because v->shadow_vqs_enabled is not valid
> > > at this time anymore.
> >
> >
> > Ok, but this doesn't explain why it is net specific but vhost-vdpa specific.
> >
>
> We can try to move it to a vhost op, but we have the same problem as
> the svq array allocation: We don't have the right place in vhost ops
> to check this. Maybe vhost_set_features is the right one here?

If we can do all the probing at the initialization phase, we can do
everything there.

Thanks

>
> Thanks!
>
> > Thanks
> >
> >
> > >
> > > Thanks!
> > >
> > >> Thanks
> > >>
> > >>
> > >>> Since the moved checks will be already evaluated at net/ to know if it
> > >>> is ok to shadow CVQ, move them.
> > >>>
> > >>> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> > >>> ---
> > >>>    hw/virtio/vhost-vdpa.c | 33 ++-------------------------------
> > >>>    net/vhost-vdpa.c       |  3 ++-
> > >>>    2 files changed, 4 insertions(+), 32 deletions(-)
> > >>>
> > >>> diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> > >>> index 3df2775760..146f0dcb40 100644
> > >>> --- a/hw/virtio/vhost-vdpa.c
> > >>> +++ b/hw/virtio/vhost-vdpa.c
> > >>> @@ -402,29 +402,9 @@ static int vhost_vdpa_get_dev_features(struct vhost_dev *dev,
> > >>>        return ret;
> > >>>    }
> > >>>
> > >>> -static int vhost_vdpa_init_svq(struct vhost_dev *hdev, struct vhost_vdpa *v,
> > >>> -                               Error **errp)
> > >>> +static void vhost_vdpa_init_svq(struct vhost_dev *hdev, struct vhost_vdpa *v)
> > >>>    {
> > >>>        g_autoptr(GPtrArray) shadow_vqs = NULL;
> > >>> -    uint64_t dev_features, svq_features;
> > >>> -    int r;
> > >>> -    bool ok;
> > >>> -
> > >>> -    if (!v->shadow_vqs_enabled) {
> > >>> -        return 0;
> > >>> -    }
> > >>> -
> > >>> -    r = vhost_vdpa_get_dev_features(hdev, &dev_features);
> > >>> -    if (r != 0) {
> > >>> -        error_setg_errno(errp, -r, "Can't get vdpa device features");
> > >>> -        return r;
> > >>> -    }
> > >>> -
> > >>> -    svq_features = dev_features;
> > >>> -    ok = vhost_svq_valid_features(svq_features, errp);
> > >>> -    if (unlikely(!ok)) {
> > >>> -        return -1;
> > >>> -    }
> > >>>
> > >>>        shadow_vqs = g_ptr_array_new_full(hdev->nvqs, vhost_svq_free);
> > >>>        for (unsigned n = 0; n < hdev->nvqs; ++n) {
> > >>> @@ -436,7 +416,6 @@ static int vhost_vdpa_init_svq(struct vhost_dev *hdev, struct vhost_vdpa *v,
> > >>>        }
> > >>>
> > >>>        v->shadow_vqs = g_steal_pointer(&shadow_vqs);
> > >>> -    return 0;
> > >>>    }
> > >>>
> > >>>    static int vhost_vdpa_init(struct vhost_dev *dev, void *opaque, Error **errp)
> > >>> @@ -461,11 +440,7 @@ static int vhost_vdpa_init(struct vhost_dev *dev, void *opaque, Error **errp)
> > >>>        dev->opaque =  opaque ;
> > >>>        v->listener = vhost_vdpa_memory_listener;
> > >>>        v->msg_type = VHOST_IOTLB_MSG_V2;
> > >>> -    ret = vhost_vdpa_init_svq(dev, v, errp);
> > >>> -    if (ret) {
> > >>> -        goto err;
> > >>> -    }
> > >>> -
> > >>> +    vhost_vdpa_init_svq(dev, v);
> > >>>        vhost_vdpa_get_iova_range(v);
> > >>>
> > >>>        if (!vhost_vdpa_first_dev(dev)) {
> > >>> @@ -476,10 +451,6 @@ static int vhost_vdpa_init(struct vhost_dev *dev, void *opaque, Error **errp)
> > >>>                                   VIRTIO_CONFIG_S_DRIVER);
> > >>>
> > >>>        return 0;
> > >>> -
> > >>> -err:
> > >>> -    ram_block_discard_disable(false);
> > >>> -    return ret;
> > >>>    }
> > >>>
> > >>>    static void vhost_vdpa_host_notifier_uninit(struct vhost_dev *dev,
> > >>> diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
> > >>> index d3b1de481b..fb35b17ab4 100644
> > >>> --- a/net/vhost-vdpa.c
> > >>> +++ b/net/vhost-vdpa.c
> > >>> @@ -117,9 +117,10 @@ static bool vhost_vdpa_net_valid_svq_features(uint64_t features, Error **errp)
> > >>>        if (invalid_dev_features) {
> > >>>            error_setg(errp, "vdpa svq does not work with features 0x%" PRIx64,
> > >>>                       invalid_dev_features);
> > >>> +        return false;
> > >>>        }
> > >>>
> > >>> -    return !invalid_dev_features;
> > >>> +    return vhost_svq_valid_features(features, errp);
> > >>>    }
> > >>>
> > >>>    static int vhost_vdpa_net_check_device_id(struct vhost_net *net)
> >
>