Re: [PATCH net 05/13] idpf: do not enable XDP if queue based scheduling is not supported

[Jacob Keller <jacob.e.keller@intel.com>]

On 5/4/2026 10:14 PM, Jacob Keller wrote:
> From: Joshua Hay <joshua.a.hay@intel.com>
> 
> The current XDP implementation uses queue based scheduling for its TxQs.
> If the FW does not advertise support for queue based scheduling, do not
> enable XDP. Add the missing capability check at the start of the XDP
> configuration. This will temporarily break XDP while a flow based
> implementation is worked on, as well as while FWs with queue based by
> default are rolled out.
> 
> Fixes: 705457e7211f ("idpf: implement XDP_SETUP_PROG in ndo_bpf for splitq")
> Signed-off-by: Joshua Hay <joshua.a.hay@intel.com>
> Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
> Reviewed-by: Madhu Chittim <madhu.chittim@intel.com>
> Tested-by: Patryk Holda <patryk.holda@intel.com>
> Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
> ---
>  drivers/net/ethernet/intel/idpf/xdp.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/net/ethernet/intel/idpf/xdp.c b/drivers/net/ethernet/intel/idpf/xdp.c
> index cbccd4546768..dcd867517a5f 100644
> --- a/drivers/net/ethernet/intel/idpf/xdp.c
> +++ b/drivers/net/ethernet/intel/idpf/xdp.c
> @@ -510,6 +510,13 @@ int idpf_xdp(struct net_device *dev, struct netdev_bpf *xdp)
>  	if (!idpf_is_queue_model_split(vport->dflt_qv_rsrc.txq_model))
>  		goto notsupp;
>  
> +	if (!idpf_is_cap_ena(vport->adapter, IDPF_OTHER_CAPS,
> +			     VIRTCHNL2_CAP_SPLITQ_QSCHED)) {
> +		NL_SET_ERR_MSG_MOD(xdp->extack,
> +				   "Device does not support requested XDP Tx scheduling mode");
> +		goto notsupp;
> +	}
> +

Sashiko points out that this is only valid for XDP_SETUP_PROG:

> Could accessing xdp->extack here cause an uninitialized memory dereference?
> idpf_xdp() handles multiple commands like XDP_SETUP_PROG and
> XDP_SETUP_XSK_POOL. In struct netdev_bpf, extack is part of a union and
> is only valid when xdp->command is XDP_SETUP_PROG.
> Since this capability check happens before the switch (xdp->command) block,
> if the command is XDP_SETUP_XSK_POOL, xdp->extack overlaps with the xsk
> sub-struct and might contain uninitialized stack data.
> If that memory is non-NULL, NL_SET_ERR_MSG_MOD could write the error message
> pointer to an arbitrary memory address.
> Should this capability check be moved inside the XDP_SETUP_PROG case,
> or should the command type be verified before accessing xdp->extack?

I checked and the netdev_bpf structure indeed only has extack for the
XDP_SETUP_PROG case.

Because extack is only valid for that command, you can't use extack here.

I don't know if this check either belongs inside idpf_xdp_setup_prog()
or if you should just call NL_SET_ERR_MSG_MOD if it is an XDP_SETUP_PROG.

Josh, could you figure out which solution is better and prepare an
updated version.

>  	switch (xdp->command) {
>  	case XDP_SETUP_PROG:
>  		ret = idpf_xdp_setup_prog(vport, xdp);
>