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

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

On 2023-03-11 p.m.2:05, Michael S. Tsirkin wrote:
> External email: Use caution opening links or attachments
> 
> 
> 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?
> 
Hi Michael

I will construct a non power of 2 size packed virtqueue device to test 
whether the driver is loaded successfully and whether the traffic is 
normal; at the same time, I will also construct a non power of 2 size 
split virtqueue device for testing to see if an warning is given and the 
driver is loaded fail

The method of constructing the device, such as the reply steps in the 
previous email
> 
> --
> MST
>