Re: [RFC] virtio-net: support modern-transtional devices

["Michael S. Tsirkin" <mst@redhat.com>]

On Sat, May 27, 2023 at 02:15:42AM +0800, Zhu Lingshan wrote:
> Current virtio-net only probes a device with VIRITO_ID_NET == 1.
> 
> For a modern-transtional virtio-net device which has a transtional
> device id 0x1000 and acts as a modern device, current virtio-pci
> modern driver will assign the sub-device-id to its mdev->id.device,
> which may not be 0x1, this sub-device-id is up to the vendor.
> 
> That means virtio-net driver doesn't probe a modern-transitonal
> virtio-net with a sub-device-id other than 0x1, which is a bug.

No, the bug is in the device. Legacy linux drivers always looked at
sub device id (other OSes might differ). So it makes no sense
for a transitional device to have sub-device-id other than 0x1.
Don't have time to look at spec but I think you will find it there.


> Other types of devices also have similar issues, like virito-blk.
> 
> I propose to fix this problem of modern-transitonal device
> whith this solution, all in the modern code path:
> 1) assign the device id to mdev->id.device
> 2) add transitional device ids in the virtio-net(and others) probe table.
> 
> Comments are welcome!
> 
> Thanks!
> 
> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
> ---
>  drivers/net/virtio_net.c               | 1 +
>  drivers/virtio/virtio_pci_modern_dev.c | 2 +-
>  2 files changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 56ca1d270304..6b45d8602a6b 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -4250,6 +4250,7 @@ static __maybe_unused int virtnet_restore(struct virtio_device *vdev)
>  
>  static struct virtio_device_id id_table[] = {
>  	{ VIRTIO_ID_NET, VIRTIO_DEV_ANY_ID },
> +	{ VIRTIO_TRANS_ID_NET, VIRTIO_DEV_ANY_ID },
>  	{ 0 },
>  };
>  
> diff --git a/drivers/virtio/virtio_pci_modern_dev.c b/drivers/virtio/virtio_pci_modern_dev.c
> index 869cb46bef96..80846e1195ce 100644
> --- a/drivers/virtio/virtio_pci_modern_dev.c
> +++ b/drivers/virtio/virtio_pci_modern_dev.c
> @@ -229,7 +229,7 @@ int vp_modern_probe(struct virtio_pci_modern_device *mdev)
>  		/* Transitional devices: use the PCI subsystem device id as
>  		 * virtio device id, same as legacy driver always did.
>  		 */
> -		mdev->id.device = pci_dev->subsystem_device;
> +		mdev->id.device = pci_dev->device;
>  	} else {
>  		/* Modern devices: simply use PCI device id, but start from 0x1040. */
>  		mdev->id.device = pci_dev->device - 0x1040;
> -- 
> 2.39.1

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