Re: [net-next, v2 1/2] psp: Support for transmit on logical device when the underlying transport device supports PSP.

[Daniel Zahka <daniel.zahka@gmail.com>]

On 2/23/26 2:11 PM, Kiran Kella wrote:
> This is achieved by propagating the psp_dev from the lower device
> to the upper devices in the device stack via a netdevice notifier.
> The lowest device owns the psp_dev pointer while the upper devices
> just borrow the pointer. When the lower device is unlinked, the
> borrowed pointer is cleared in the upper device.
> Assumption being that psp_dev is set on the lowest device before
> any upper devices are stacked on that lowest device.
>
> Signed-off-by: Kiran Kella <kiran.kella@broadcom.com>
> Reviewed-by: Ajit Kumar Khaparde <ajit.khaparde@broadcom.com>
> Reviewed-by: Akhilesh Samineni <akhilesh.samineni@broadcom.com>
> ---
>   net/psp/psp_main.c | 109 ++++++++++++++++++++++++++++++++++++++++++++-
>   1 file changed, 108 insertions(+), 1 deletion(-)
>
> diff --git a/net/psp/psp_main.c b/net/psp/psp_main.c
> index a8534124f626..fac785dcfa0f 100644
> --- a/net/psp/psp_main.c
> +++ b/net/psp/psp_main.c
> @@ -3,6 +3,7 @@
>   #include <linux/bitfield.h>
>   #include <linux/list.h>
>   #include <linux/netdevice.h>
> +#include <linux/rtnetlink.h>
>   #include <linux/xarray.h>
>   #include <net/net_namespace.h>
>   #include <net/psp.h>
> @@ -110,13 +111,45 @@ void psp_dev_free(struct psp_dev *psd)
>   	kfree_rcu(psd, rcu);
>   }
>   
> +/**
> + * psp_clear_upper_dev_psp_dev() - Clear borrowed psp_dev pointer on upper
> + *				   device
> + * @upper_dev:	Upper device that may have borrowed psp_dev pointer
> + * @priv:	netdev_nested_priv containing the psp_dev being unregistered
> + *
> + * Callback for netdev_walk_all_upper_dev_rcu() to clear borrowed psp_dev
> + * pointers on upper devices when the underlying psp_dev is being unregistered.
> + *
> + * Return: 0 to continue walking, non-zero to stop.
> + */
> +static int psp_clear_upper_dev_psp_dev(struct net_device *upper_dev,
> +				       struct netdev_nested_priv *priv)
> +{
> +	struct psp_dev *psd = priv->data;
> +	struct psp_dev *upper_psd;
> +
> +	upper_psd = rcu_dereference(upper_dev->psp_dev);
> +	if (upper_psd == psd)
> +		rcu_assign_pointer(upper_dev->psp_dev, NULL);
> +
> +	return 0;
> +}
> +
>   /**
>    * psp_dev_unregister() - unregister PSP device
>    * @psd:	PSP device structure
> + *
> + * Unregisters a PSP device and clears all borrowed psp_dev pointers on
> + * upper devices (e.g., VLAN subinterfaces) that reference this device.
> + * This prevents use-after-free if upper devices still have borrowed
> + * pointers when the psp_dev structure is freed.
>    */
>   void psp_dev_unregister(struct psp_dev *psd)
>   {
>   	struct psp_assoc *pas, *next;
> +	struct netdev_nested_priv priv = {
> +		.data = psd,
> +	};
>   
>   	mutex_lock(&psp_devs_lock);
>   	mutex_lock(&psd->lock);
> @@ -137,6 +170,12 @@ void psp_dev_unregister(struct psp_dev *psd)
>   
>   	rcu_assign_pointer(psd->main_netdev->psp_dev, NULL);
>   
> +	/* Clear borrowed psp_dev pointers on all upper devices */
> +	rcu_read_lock();
> +	netdev_walk_all_upper_dev_rcu(psd->main_netdev,
> +				      psp_clear_upper_dev_psp_dev, &priv);
> +	rcu_read_unlock();
> +
>   	psd->ops = NULL;
>   	psd->drv_priv = NULL;
>   
> @@ -313,11 +352,79 @@ int psp_dev_rcv(struct sk_buff *skb, u16 dev_id, u8 generation, bool strip_icv)
>   }
>   EXPORT_SYMBOL(psp_dev_rcv);
>   
> +/**
> + * psp_netdevice_event() - Handle netdevice events for PSP device propagation
> + * @nb:		notifier block
> + * @event:	netdevice event
> + * @ptr:	netdevice notifier info
> + *
> + * Propagates psp_dev pointer from lower devices to upper devices when
> + * upper devices are created (e.g., VLAN subinterfaces).
> + * Excluding from this logic, the upper devices that have multiple lower
> + * devices eg., bond devices.
> + *
> + * Return: NOTIFY_DONE
> + */
> +static int psp_netdevice_event(struct notifier_block *nb,
> +			       unsigned long event, void *ptr)
> +{
> +	struct netdev_notifier_changeupper_info *info;
> +	struct net_device *dev, *upper_dev;
> +	struct psp_dev *psd;
> +
> +	if (event != NETDEV_CHANGEUPPER)
> +		return NOTIFY_DONE;
> +
> +	info = ptr;
> +	dev = netdev_notifier_info_to_dev(ptr);
> +	upper_dev = info->upper_dev;
> +
> +	if (netif_is_lag_master(upper_dev))
> +		return NOTIFY_DONE;
> +
> +	if (info->linking) {
> +		/* Lower device is being linked to an upper device.
> +		 * Propagate psp_dev from the immediate lower device to the
> +		 * upper device. The immediate lower device would have already
> +		 * got the psp_dev pointer set in a previous notification (or
> +		 * owns it if it's the lowest device).
> +		 * Upper devices just borrow the pointer.
> +		 */
> +		psd = rtnl_dereference(dev->psp_dev);
> +		if (psd)
> +			rcu_assign_pointer(upper_dev->psp_dev, psd);
> +	} else {
> +		/* Lower device is being unlinked from an upper device.
> +		 * Clear the borrowed psp_dev pointer.
> +		 */
> +		psd = rtnl_dereference(upper_dev->psp_dev);
> +		if (psd)
> +			rcu_assign_pointer(upper_dev->psp_dev, NULL);
> +	}
> +
> +	return NOTIFY_DONE;
> +}
> +
> +static struct notifier_block psp_netdevice_notifier = {
> +	.notifier_call = psp_netdevice_event,
> +};
> +
>   static int __init psp_init(void)
>   {
> +	int err;
> +
>   	mutex_init(&psp_devs_lock);
>   
> -	return genl_register_family(&psp_nl_family);
> +	err = register_netdevice_notifier(&psp_netdevice_notifier);
> +	if (err)
> +		return err;
> +
> +	err = genl_register_family(&psp_nl_family);
> +	if (err) {
> +		unregister_netdevice_notifier(&psp_netdevice_notifier);
> +		return err;
> +	}
> +	return 0;
>   }
>   
>   subsys_initcall(psp_init);

The lack of support for netns is a bit of a gap for this feature. It may 
make sense to see if what was posted in 
https://lore.kernel.org/netdev/20260224002410.1553838-1-weibunny@fb.com/ 
is sufficient for your use case, as it handles cases where upper devices 
are in a different netns from psd->main_netdev.