net/mlx5e: RX, Fix generating skb from non-linear xdp_buff for legacy RQ

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: ea5d49b ("net/mlx5e: Add XDP multi buffer support to the non-linear legacy RQ")
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Signed-off-by: Amery Hung <ameryhung@gmail.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/1760644540-899148-2-git-send-email-tariqt@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: ameryhung

drivers/net/ethernet/mellanox/mlx5/core/en_rx.c

@@ -1794,14 +1794,27 @@ mlx5e_skb_from_cqe_nonlinear(struct mlx5e_rq *rq, struct mlx5e_wqe_frag_info *wi
 	}
 
 	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;
+	if (prog) {
+		u8 nr_frags_free, old_nr_frags = sinfo->nr_frags;
+
+		if (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 */
+		}
 
-			for (pwi = head_wi; pwi < wi; pwi++)
-				pwi->frag_page->frags++;
+		nr_frags_free = old_nr_frags - sinfo->nr_frags;
+		if (unlikely(nr_frags_free)) {
+			wi -= nr_frags_free;
+			truesize -= nr_frags_free * frag_info->frag_stride;
 		}
-		return NULL; /* page/packet was consumed by XDP */
 	}
 
 	skb = mlx5e_build_linear_skb(