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

[Kiran Kella]

On Wed, Feb 25, 2026 at 2:28 AM Daniel Zahka <daniel.zahka@xxxxxxxxx> wrote:
>
>
>
> 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@xxxxxxxxxxxx>
> > Reviewed-by: Ajit Kumar Khaparde <ajit.khaparde@xxxxxxxxxxxx>
> > Reviewed-by: Akhilesh Samineni <akhilesh.samineni@xxxxxxxxxxxx>
> > ---
> >   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@xxxxxx/
> is sufficient for your use case, as it handles cases where upper devices
> are in a different netns from psd->main_netdev.

Thanks. Went through the changes in
https://lore.kernel.org/netdev/20260224002410.1553838-1-weibunny@xxxxxx/
It is sufficient for my use case too, although it specifically
addresses the cross-netns virtual devices use case.
But the same net-ns stacked devices like VLANs can be handled with
this patch implicitly, without user intervention through dev-assoc.
I think both approaches can co-exist without conflict.
However, I am ok with using a single approach to use the dev-assoc for
the same net-ns use case too.

Thanks,
Kiran