On Wed, Sep 10, 2025 at 12:24 PM Dragos Tatulea <dtatulea@xxxxxxxxxx> wrote:
>
> On Tue, Sep 09, 2025 at 08:41:02PM -0700, Amery Hung wrote:
> > XDP programs can release xdp_buff fragments when calling
> > bpf_xdp_adjust_tail(). The driver currently assumes the number of
> > fragments to be unchanged and may generate skb with wrong truesize or
> > containing invalid frags. Fix the bug by generating skb according to
> > xdp_buff after the XDP program runs.
> >
> > Fixes: ea5d49bdae8b ("net/mlx5e: Add XDP multi buffer support to the non-linear legacy RQ")
> > Signed-off-by: Amery Hung <ameryhung@xxxxxxxxx>
> > ---
> > drivers/net/ethernet/mellanox/mlx5/core/en_rx.c | 9 +++++++++
> > 1 file changed, 9 insertions(+)
> >
> > diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
> > index b8c609d91d11..1d3eacfd0325 100644
> > --- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
> > +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
> > @@ -1729,6 +1729,7 @@ mlx5e_skb_from_cqe_nonlinear(struct mlx5e_rq *rq, struct mlx5e_wqe_frag_info *wi
> > struct mlx5e_wqe_frag_info *head_wi = wi;
> > u16 rx_headroom = rq->buff.headroom;
> > struct mlx5e_frag_page *frag_page;
> > + u8 nr_frags_free, old_nr_frags;
> > struct skb_shared_info *sinfo;
> > u32 frag_consumed_bytes;
> > struct bpf_prog *prog;
> > @@ -1772,17 +1773,25 @@ mlx5e_skb_from_cqe_nonlinear(struct mlx5e_rq *rq, struct mlx5e_wqe_frag_info *wi
> > wi++;
> > }
> >
> > + old_nr_frags = sinfo->nr_frags;
> > +
> > prog = rcu_dereference(rq->xdp_prog);
> > if (prog && mlx5e_xdp_handle(rq, prog, mxbuf)) {
> > if (__test_and_clear_bit(MLX5E_RQ_FLAG_XDP_XMIT, rq->flags)) {
> > struct mlx5e_wqe_frag_info *pwi;
> >
> > + wi -= old_nr_frags - sinfo->nr_frags;
> > +
> > for (pwi = head_wi; pwi < wi; pwi++)
> > pwi->frag_page->frags++;
> > }
> > return NULL; /* page/packet was consumed by XDP */
> > }
> >
> > + nr_frags_free = old_nr_frags - sinfo->nr_frags;
> Just double checking that my understanding is correct:
> bpf_xdp_adjust_tail() can increase the tail only up to fragment limit,
> right? So this operation can always be >= 0.
>
Right, AFAIK bpf programs cannot add fragments to xdp_buff.
> If yes:
> Reviewed-by: Dragos Tatulea <dtatulea@xxxxxxxxxx>
>
> Thanks,
> Dragos
