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 10:13:27 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Eli Cohen <elic@...dia.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 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