Re: [PATCH] vdpa: set old virtio status at cvq isolation probing end

[Eugenio Perez Martin]

On Wed, Jul 26, 2023 at 4:07 AM Jason Wang <jasowang@redhat.com> wrote:
>
> On Wed, Jul 26, 2023 at 2:21 AM Eugenio Pérez <eperezma@redhat.com> wrote:
> >
> > The device already has a virtio status set by vhost_vdpa_init by the
> > time vhost_vdpa_probe_cvq_isolation is called. vhost_vdpa_init set
> > S_ACKNOWLEDGE and S_DRIVER, so it is invalid to just reset it.
> >
> > It is invalid to start the device after it, but all devices seems to be
> > fine with it.  Fixing qemu so it follows virtio start procedure.
> >
> > Fixes: 152128d64697 ("vdpa: move CVQ isolation check to 
> > net_init_vhost_vdpa")
> > Reported-by: Dragos Tatulea <dtatulea@nvidia.com>
> > Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> > ---
> >  net/vhost-vdpa.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
> > index 9795306742..d7e2b714b4 100644
> > --- a/net/vhost-vdpa.c
> > +++ b/net/vhost-vdpa.c
> > @@ -1333,6 +1333,8 @@ static int vhost_vdpa_probe_cvq_isolation(int 
> > device_fd, uint64_t features,
> >  out:
> >      status = 0;
> >      ioctl(device_fd, VHOST_VDPA_SET_STATUS, &status);
> > +    status = VIRTIO_CONFIG_S_ACKNOWLEDGE | VIRTIO_CONFIG_S_DRIVER;
> > +    ioctl(device_fd, VHOST_VDPA_SET_STATUS, &status);
>
> So if we fail after FEATURES_OK, this basically clears that bit. Spec
> doesn't say it can or not, I wonder if a reset is better?
>

I don't follow this, the reset is just above the added code, isn't it?

> Btw, spec requires a read of status after setting FEATURES_OK, this
> seems to be missed in the current code.
>

I'm ok with that, but this patch does not touch that part.

To fix this properly we should:
- Expose vhost_vdpa_set_dev_features_fd as we did in previous versions
of the series that added vhost_vdpa_probe_cvq_isolation [1].
- Get status after vhost_vdpa_add_status, so both vhost start code and
this follows the standard properly.

Is it ok to do these on top of this patch?

Thanks!

[1] 
https://lore.kernel.org/qemu-devel/20230509154435.1410162-4-eperezma@redhat.com/


> Thanks
>
> >      return r;
> >  }
> >
> > --
> > 2.39.3
> >
>