Re: [PATCH net] mediathek: mtk_eth_soc: fix netdev inside xdp_rxq_info

[Lorenzo Bianconi <lorenzo@kernel.org>]

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> On Tue, Nov 26, 2024 at 07:16:00PM +0100, Lorenzo Bianconi wrote:
> > > Currently, the network device isn't set inside the xdp_rxq_info
> > > of the mtk_rx_ring, which means that an XDP program attached to
> > > the Mediathek ethernet driver cannot retrieve the index of the
> > > interface that received the package since it's always 0 inside
> > > the xdp_md struct.
> > > 
> > > This patch sets the network device pointer inside the
> > > xdp_rxq_info struct, which is later used to initialize
> > > the xdp_buff struct via xdp_init_buff.
> > > 
> > > This was tested using the following eBPF/XDP program attached
> > > to a network interface of the mtk_eth_soc driver. As said before,
> > > ingress_ifindex always had a value of zero. After applying the
> > > patch, ingress_ifindex holds the correct interface index.
> > > 
> > > 	#include <linux/bpf.h>
> > > 	#include <bpf/bpf_helpers.h>
> > > 
> > > 	SEC("pass")
> > > 	int pass_func(struct xdp_md *xdp) {
> > >     		bpf_printk("ingress_ifindex: %u",
> > > 			xdp->ingress_ifindex);
> > > 
> > > 		return XDP_PASS;
> > > 	}
> > > 
> > > 	char _license[] SEC("license") = "GPL";
> > > 
> > > Signed-off-by: Til Kaiser <mail@tk154.de>
> > > ---
> > >  drivers/net/ethernet/mediatek/mtk_eth_soc.c | 1 +
> > >  1 file changed, 1 insertion(+)
> > > 
> > > diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> > > index 53485142938c..9c6d4477e536 100644
> > > --- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> > > +++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> > > @@ -2069,6 +2069,7 @@ static int mtk_poll_rx(struct napi_struct *napi, int budget,
> > >  
> > >  		netdev = eth->netdev[mac];
> > >  		ppe_idx = eth->mac[mac]->ppe_idx;
> > > +		ring->xdp_q.dev = netdev;
> > 
> > I guess you can set it just before running xdp_init_buff(), but the change is fine.
> 
> Lorenzo, is it legitimate to change rxq->dev post registration like
> that?
> 
> I am asking because we have a similar problem [1]. In our case we also
> register the rxq structure with a dummy netdev which is why XDP programs
> see an ifindex of 0.

to be honest I was thinking about it but I guess the dev pointer is just used
running the eBPF program.
@Jesper: any concern?

Regards,
Lorenzo

> 
> Thanks
> 
> [1] https://lore.kernel.org/netdev/ZzYR2ZJ1mGRq12VL@shredder/
> 
> > 
> > Regards,
> > Lorenzo
> > 
> > >  
> > >  		if (unlikely(test_bit(MTK_RESETTING, &eth->state)))
> > >  			goto release_desc;
> > > -- 
> > > 2.47.1
> > > 
> > > 
> 
> 

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