Linux Virtualization - Mar 2023 - [PATCH v2 1/3] virtio_pci_modern: Allow non power of 2 sizes for virtqueues

On 2023-03-10 a.m.8:36, Parav Pandit wrote:
> 
> 
>> From: Feng Liu <feliu at nvidia.com>
>> Sent: Friday, March 10, 2023 12:34 AM
> 
>>
>> -	if (!is_power_of_2(num)) {
>> -		dev_warn(&vp_dev->pci_dev->dev, "bad queue size
%u",
>> num);
>> -		return ERR_PTR(-EINVAL);
>> -	}
>> -
> 
> The check is still valid for split q.
> Maybe the right place for such a check is not the pci transport driver.
> But layer below where split vs packed q knowledge resides and hence, power
of 2 check can be omitted for packed vq.
Hi, Parav
     I think you are right, I checked the virtio spec, only packed 
virtqueue can use queue size which is not power_of_2; so, I think the 
check can be reserved only for split queue here, something like

struct virtio_device *vdev = &vp_dev->vdev;
if (!virtio_has_feature(vdev, VIRTIO_F_RING_PACKED)
  && !is_power_of_2(num)){
     dev_warn(&vp_dev->pci_dev->dev, "bad queue size %u",
num);
     return ERR_PTR(-EINVAL);
}

I will fix it in next version

Hi, Michael and Jason
Do you have any comments on this?

On Fri, Mar 10, 2023 at 10:23:16AM -0500, Feng Liu
wrote:
> 
> 
> On 2023-03-10 a.m.8:36, Parav Pandit wrote:
> > 
> > 
> > > From: Feng Liu <feliu at nvidia.com>
> > > Sent: Friday, March 10, 2023 12:34 AM
> > 
> > > 
> > > -	if (!is_power_of_2(num)) {
> > > -		dev_warn(&vp_dev->pci_dev->dev, "bad queue size
%u",
> > > num);
> > > -		return ERR_PTR(-EINVAL);
> > > -	}
> > > -
> > 
> > The check is still valid for split q.
> > Maybe the right place for such a check is not the pci transport
driver.
> > But layer below where split vs packed q knowledge resides and hence,
power of 2 check can be omitted for packed vq.
> 
> Hi, Parav
>     I think you are right, I checked the virtio spec, only packed virtqueue
> can use queue size which is not power_of_2; so, I think the check can be
> reserved only for split queue here, something like
> 
> struct virtio_device *vdev = &vp_dev->vdev;
> if (!virtio_has_feature(vdev, VIRTIO_F_RING_PACKED)
>  && !is_power_of_2(num)){
>     dev_warn(&vp_dev->pci_dev->dev, "bad queue size
%u", num);
>     return ERR_PTR(-EINVAL);
> }
> 
> I will fix it in next version
> 
> Hi, Michael and Jason
> Do you have any comments on this?
> 
Hmm good point. Which raises the question: so how did you test it then?


-- 
MST