Re: [PATCH v1] vdpa/vdpa_sim: Use the negotiated features when calling vringh_init_iotlb

[Stefano Garzarella]

On Tue, Jul 20, 2021 at 10:14:35AM +0300, Eli Cohen wrote:
> On Tue, Jul 20, 2021 at 08:57:40AM +0200, Stefano Garzarella wrote:
> > On Tue, Jul 20, 2021 at 08:25:33AM +0300, Eli Cohen wrote:
> > > When calling vringh_init_iotlb(), use the negotiated features which
> > > might be different than the supported features.
> > >
> > > Fixes: 2c53d0f64c06f ("vdpasim: vDPA device simulator")
> > > Signed-off-by: Eli Cohen <elic@xxxxxxxxxx>
> > > ---
> > > v0 --> v1:
> > > Update "Fixes" line
> > >
> > > drivers/vdpa/vdpa_sim/vdpa_sim.c | 4 ++--
> > > 1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> > > index 14e024de5cbf..89a474c7a096 100644
> > > --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
> > > +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> > > @@ -66,7 +66,7 @@ static void vdpasim_queue_ready(struct vdpasim *vdpasim, unsigned int idx)
> > > {
> > > 	struct vdpasim_virtqueue *vq = &vdpasim->vqs[idx];
> > >
> > > -	vringh_init_iotlb(&vq->vring, vdpasim->dev_attr.supported_features,
> > > +	vringh_init_iotlb(&vq->vring, vdpasim->features,
> > > 			  VDPASIM_QUEUE_MAX, false,
> > > 			  (struct vring_desc *)(uintptr_t)vq->desc_addr,
> > > 			  (struct vring_avail *)
> > > @@ -86,7 +86,7 @@ static void vdpasim_vq_reset(struct vdpasim *vdpasim,
> > > 	vq->device_addr = 0;
> > > 	vq->cb = NULL;
> > > 	vq->private = NULL;
> > > -	vringh_init_iotlb(&vq->vring, vdpasim->dev_attr.supported_features,
> > > +	vringh_init_iotlb(&vq->vring, vdpasim->features,
> >
> > vdpasim_vq_reset() is called while resetting the device in vdpasim_reset()
> > where we also set `vdpasim->features = 0` after resetting the vqs, so maybe
> > it's better to use the supported features here, since the negotiated ones
> > are related to the previous instance.
>
> I don't think using supported features is valid. Better to make sure
> vringh_init_iotlb() is called after the features have been negotiated.

I think the vringh_init_iotlb() call in vdpasim_vq_reset() is just used 
to clean up the `struct vringh`, then it will be initialized in 
vdpasim_queue_ready() when features have already been negotiated.

Maybe here we can pass 0 (to the features parameter) if we don't want to 
use the features supported by the device.

Thanks,
Stefano