Re: [PATCH] vhost-vdpa: check vhost_vdpa_set_vring_ready() return value

[Stefano Garzarella]

On Thu, Mar 14, 2024 at 11:17:01AM +0800, Jason Wang wrote:
> On Wed, Feb 7, 2024 at 5:27 PM Stefano Garzarella <sgarzare@redhat.com> wrote:
> > vhost_vdpa_set_vring_ready() could already fail, but if Linux's
> > patch [1] will be merged, it may fail with more chance if
> > userspace does not activate virtqueues before DRIVER_OK when
> > VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK is not negotiated.
>
> I wonder what happens if we just leave it as is.

Are you referring to this patch or the kernel patch?

Here I'm just checking the return value of vhost_vdpa_set_vring_ready().
It can return an error also without that kernel patch, so IMHO is
better to check the return value here in QEMU.

What issue do you see with this patch applied?

> VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK: We do know enabling could be
> done after driver_ok.
> Without VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK: We don't know whether
> enabling could be done after driver_ok or not.

I see your point, indeed I didn't send a v2 of that patch.
Maybe we should document that, because it could be interpreted that if
VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK is not negotiated the enabling
should always be done before driver_ok (which is true for example in
VDUSE).

BTW I think we should discuss it in the kernel patch.

Thanks,
Stefano

> Thanks
>
> > So better check its return value anyway.
> >
> > [1] 
> > https://lore.kernel.org/virtualization/20240206145154.118044-1-sgarzare@redhat.com/T/#u
> >
> > Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> > ---
> > Note: This patch conflicts with [2], but the resolution is simple,
> > so for now I sent a patch for the current master, but I'll rebase
> > this patch if we merge the other one first.
> >
> > [2] 
> > https://lore.kernel.org/qemu-devel/20240202132521.32714-1-kwolf@redhat.com/
> > ---
> >  hw/virtio/vdpa-dev.c |  8 +++++++-
> >  net/vhost-vdpa.c     | 15 ++++++++++++---
> >  2 files changed, 19 insertions(+), 4 deletions(-)
> >
> > diff --git a/hw/virtio/vdpa-dev.c b/hw/virtio/vdpa-dev.c
> > index eb9ecea83b..d57cd76c18 100644
> > --- a/hw/virtio/vdpa-dev.c
> > +++ b/hw/virtio/vdpa-dev.c
> > @@ -259,7 +259,11 @@ static int vhost_vdpa_device_start(VirtIODevice *vdev, 
> > Error **errp)
> >          goto err_guest_notifiers;
> >      }
> >      for (i = 0; i < s->dev.nvqs; ++i) {
> > -        vhost_vdpa_set_vring_ready(&s->vdpa, i);
> > +        ret = vhost_vdpa_set_vring_ready(&s->vdpa, i);
> > +        if (ret < 0) {
> > +            error_setg_errno(errp, -ret, "Error starting vring %d", i);
> > +            goto err_dev_stop;
> > +        }
> >      }
> >      s->started = true;
> >
> > @@ -274,6 +278,8 @@ static int vhost_vdpa_device_start(VirtIODevice *vdev, 
> > Error **errp)
> >
> >      return ret;
> >
> > +err_dev_stop:
> > +    vhost_dev_stop(&s->dev, vdev, false);
> >  err_guest_notifiers:
> >      k->set_guest_notifiers(qbus->parent, s->dev.nvqs, false);
> >  err_host_notifiers:
> > diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
> > index 3726ee5d67..e3d8036479 100644
> > --- a/net/vhost-vdpa.c
> > +++ b/net/vhost-vdpa.c
> > @@ -381,7 +381,10 @@ static int vhost_vdpa_net_data_load(NetClientState *nc)
> >      }
> >
> >      for (int i = 0; i < v->dev->nvqs; ++i) {
> > -        vhost_vdpa_set_vring_ready(v, i + v->dev->vq_index);
> > +        int ret = vhost_vdpa_set_vring_ready(v, i + v->dev->vq_index);
> > +        if (ret < 0) {
> > +            return ret;
> > +        }
> >      }
> >      return 0;
> >  }
> > @@ -1213,7 +1216,10 @@ static int vhost_vdpa_net_cvq_load(NetClientState *nc)
> >
> >      assert(nc->info->type == NET_CLIENT_DRIVER_VHOST_VDPA);
> >
> > -    vhost_vdpa_set_vring_ready(v, v->dev->vq_index);
> > +    r = vhost_vdpa_set_vring_ready(v, v->dev->vq_index);
> > +    if (unlikely(r < 0)) {
> > +        return r;
> > +    }
> >
> >      if (v->shadow_vqs_enabled) {
> >          n = VIRTIO_NET(v->dev->vdev);
> > @@ -1252,7 +1258,10 @@ static int vhost_vdpa_net_cvq_load(NetClientState *nc)
> >      }
> >
> >      for (int i = 0; i < v->dev->vq_index; ++i) {
> > -        vhost_vdpa_set_vring_ready(v, i);
> > +        r = vhost_vdpa_set_vring_ready(v, i);
> > +        if (unlikely(r < 0)) {
> > +            return r;
> > +        }
> >      }
> >
> >      return 0;
> > --
> > 2.43.0