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

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Message-ID: <20210810115418-mutt-send-email-mst@kernel.org>
Date:   Tue, 10 Aug 2021 11:55:04 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Stefano Garzarella <sgarzare@...hat.com>
Cc:     Eli Cohen <elic@...dia.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 10:13:27AM +0200, Stefano Garzarella wrote:
> 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@...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.
> > 
> 
> 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

Eli? Maybe you can describe what is the observed bug the patch
is trying to fix.

Thanks!

-- 
MST