linux-kernel - Re: [PATCH v1] vdpa/vdpa_sim: Use the negotiated features when calling vringh_init

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Date:   Tue, 20 Jul 2021 10:14:35 +0300
From:   Eli Cohen <elic@...dia.com>
To:     Stefano Garzarella <sgarzare@...hat.com>
CC:     <mst@...hat.com>, <jasowang@...hat.com>,
        <virtualization@...ts.linux-foundation.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] vdpa/vdpa_sim: Use the negotiated features when
 calling vringh_init_iotlb

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@...dia.com>
> > ---
> > 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.

> Thanks,
> Stefano
>