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

According to the Virtio Specification, the Queue Size parameter of a
virtqueue corresponds to the maximum number of descriptors in that
queue, and it does not have to be a power of 2 for packed virtqueues.
However, the virtio_pci_modern driver enforced a power of 2 check for
virtqueue sizes, which is unnecessary and restrictive for packed
virtuqueue.

Split virtqueue still needs to check the virtqueue size is power_of_2
which has been done in vring_alloc_queue_split of the virtio_ring layer.

To validate this change, we tested various virtqueue sizes for packed
rings, including 128, 256, 512, 100, 200, 500, and 1000, with
CONFIG_PAGE_POISONING enabled, and all tests passed successfully.

Signed-off-by: Feng Liu <feliu at nvidia.com>
Reviewed-by: Jiri Pirko <jiri at nvidia.com>

---
v0 -> v1
feedbacks from Jason Wang and Michael S. Tsirkin
- remove power_of_2 check of virtqueue size

v1 -> v2
feedbacks from Parav Pandit and Jiri Pirko
- keep power_of_2 check of split virtqueue in vring_alloc_queue_split of
  virtio_ring layer.
---
 drivers/virtio/virtio_pci_modern.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/drivers/virtio/virtio_pci_modern.c
b/drivers/virtio/virtio_pci_modern.c
index 9e496e288cfa..6e713904d8e8 100644
--- a/drivers/virtio/virtio_pci_modern.c
+++ b/drivers/virtio/virtio_pci_modern.c
@@ -310,11 +310,6 @@ static struct virtqueue *setup_vq(struct virtio_pci_device
*vp_dev,
 	if (!num || vp_modern_get_queue_enable(mdev, index))
 		return ERR_PTR(-ENOENT);
 
-	if (!is_power_of_2(num)) {
-		dev_warn(&vp_dev->pci_dev->dev, "bad queue size %u",
num);
-		return ERR_PTR(-EINVAL);
-	}
-
 	info->msix_vector = msix_vec;
 
 	/* create the vring */
-- 
2.34.1

On Thu, Mar 16, 2023 at 2:55?AM Feng Liu <feliu at nvidia.com>
wrote:
>
> According to the Virtio Specification, the Queue Size parameter of a
> virtqueue corresponds to the maximum number of descriptors in that
> queue, and it does not have to be a power of 2 for packed virtqueues.
> However, the virtio_pci_modern driver enforced a power of 2 check for
> virtqueue sizes, which is unnecessary and restrictive for packed
> virtuqueue.
>
> Split virtqueue still needs to check the virtqueue size is power_of_2
> which has been done in vring_alloc_queue_split of the virtio_ring layer.
>
> To validate this change, we tested various virtqueue sizes for packed
> rings, including 128, 256, 512, 100, 200, 500, and 1000, with
> CONFIG_PAGE_POISONING enabled, and all tests passed successfully.
>
> Signed-off-by: Feng Liu <feliu at nvidia.com>
> Reviewed-by: Jiri Pirko <jiri at nvidia.com>
Acked-by: Jason Wang <jasowang at redhat.com>

Thanks
>
> ---
> v0 -> v1
> feedbacks from Jason Wang and Michael S. Tsirkin
> - remove power_of_2 check of virtqueue size
>
> v1 -> v2
> feedbacks from Parav Pandit and Jiri Pirko
> - keep power_of_2 check of split virtqueue in vring_alloc_queue_split of
>   virtio_ring layer.
> ---
>  drivers/virtio/virtio_pci_modern.c | 5 -----
>  1 file changed, 5 deletions(-)
>
> diff --git a/drivers/virtio/virtio_pci_modern.c
b/drivers/virtio/virtio_pci_modern.c
> index 9e496e288cfa..6e713904d8e8 100644
> --- a/drivers/virtio/virtio_pci_modern.c
> +++ b/drivers/virtio/virtio_pci_modern.c
> @@ -310,11 +310,6 @@ static struct virtqueue *setup_vq(struct
virtio_pci_device *vp_dev,
>         if (!num || vp_modern_get_queue_enable(mdev, index))
>                 return ERR_PTR(-ENOENT);
>
> -       if (!is_power_of_2(num)) {
> -               dev_warn(&vp_dev->pci_dev->dev, "bad queue
size %u", num);
> -               return ERR_PTR(-EINVAL);
> -       }
> -
>         info->msix_vector = msix_vec;
>
>         /* create the vring */
> --
> 2.34.1
>

Feng Liu <feliu at nvidia.com> writes:
> According to the Virtio Specification, the Queue Size parameter of a
> virtqueue corresponds to the maximum number of descriptors in that
> queue, and it does not have to be a power of 2 for packed virtqueues.
> However, the virtio_pci_modern driver enforced a power of 2 check for
> virtqueue sizes, which is unnecessary and restrictive for packed
> virtuqueue.
>
> Split virtqueue still needs to check the virtqueue size is power_of_2
> which has been done in vring_alloc_queue_split of the virtio_ring layer.
>
> To validate this change, we tested various virtqueue sizes for packed
> rings, including 128, 256, 512, 100, 200, 500, and 1000, with
> CONFIG_PAGE_POISONING enabled, and all tests passed successfully.
>
> Signed-off-by: Feng Liu <feliu at nvidia.com>
> Reviewed-by: Jiri Pirko <jiri at nvidia.com>
>
Reviewed-by: David Edmondson <david.edmondson at oracle.com>
> ---
> v0 -> v1
> feedbacks from Jason Wang and Michael S. Tsirkin
> - remove power_of_2 check of virtqueue size
>
> v1 -> v2
> feedbacks from Parav Pandit and Jiri Pirko
> - keep power_of_2 check of split virtqueue in vring_alloc_queue_split of
>   virtio_ring layer.
> ---
>  drivers/virtio/virtio_pci_modern.c | 5 -----
>  1 file changed, 5 deletions(-)
>
> diff --git a/drivers/virtio/virtio_pci_modern.c
b/drivers/virtio/virtio_pci_modern.c
> index 9e496e288cfa..6e713904d8e8 100644
> --- a/drivers/virtio/virtio_pci_modern.c
> +++ b/drivers/virtio/virtio_pci_modern.c
> @@ -310,11 +310,6 @@ static struct virtqueue *setup_vq(struct
virtio_pci_device *vp_dev,
>  	if (!num || vp_modern_get_queue_enable(mdev, index))
>  		return ERR_PTR(-ENOENT);
>  
> -	if (!is_power_of_2(num)) {
> -		dev_warn(&vp_dev->pci_dev->dev, "bad queue size %u",
num);
> -		return ERR_PTR(-EINVAL);
> -	}
> -
>  	info->msix_vector = msix_vec;
>  
>  	/* create the vring */
> -- 
> 2.34.1
-- 
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