libeth, idpf: use truesize as XDP RxQ info frag_size

The only user of frag_size field in XDP RxQ info is
bpf_xdp_frags_increase_tail(). It clearly expects whole buffer size instead
of DMA write size. Different assumptions in idpf driver configuration lead
to negative tailroom.

To make it worse, buffer sizes are not actually uniform in idpf when
splitq is enabled, as there are several buffer queues, so rxq->rx_buf_size
is meaningless in this case.

Use truesize of the first bufq in AF_XDP ZC, as there is only one. Disable
growing tail for regular splitq.

Fixes: ac8a861 ("idpf: prepare structures to support XDP")
Reviewed-by: Aleksandr Loktionov <[email protected]>
Signed-off-by: Larysa Zaremba <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: walking-machine

drivers/net/ethernet/intel/idpf/xdp.c

@@ -47,12 +47,16 @@ static int __idpf_xdp_rxq_info_init(struct idpf_rx_queue *rxq, void *arg)
 {
 	const struct idpf_vport *vport = rxq->q_vector->vport;
 	const struct idpf_q_vec_rsrc *rsrc;
+	u32 frag_size = 0;
 	bool split;
 	int err;
 
+	if (idpf_queue_has(XSK, rxq))
+		frag_size = rxq->bufq_sets[0].bufq.truesize;
+
 	err = __xdp_rxq_info_reg(&rxq->xdp_rxq, vport->netdev, rxq->idx,
 				 rxq->q_vector->napi.napi_id,
-				 rxq->rx_buf_size);
+				 frag_size);
 	if (err)
 		return err;
 

drivers/net/ethernet/intel/idpf/xsk.c

@@ -403,6 +403,7 @@ int idpf_xskfq_init(struct idpf_buf_queue *bufq)
 	bufq->pending = fq.pending;
 	bufq->thresh = fq.thresh;
 	bufq->rx_buf_size = fq.buf_len;
+	bufq->truesize = fq.truesize;
 
 	if (!idpf_xskfq_refill(bufq))
 		netdev_err(bufq->pool->netdev,

drivers/net/ethernet/intel/libeth/xsk.c

@@ -167,6 +167,7 @@ int libeth_xskfq_create(struct libeth_xskfq *fq)
 	fq->pending = fq->count;
 	fq->thresh = libeth_xdp_queue_threshold(fq->count);
 	fq->buf_len = xsk_pool_get_rx_frame_size(fq->pool);
+	fq->truesize = xsk_pool_get_rx_frag_step(fq->pool);
 
 	return 0;
 }

include/net/libeth/xsk.h

@@ -597,6 +597,7 @@ __libeth_xsk_run_pass(struct libeth_xdp_buff *xdp,
  * @pending: current number of XSkFQEs to refill
  * @thresh: threshold below which the queue is refilled
  * @buf_len: HW-writeable length per each buffer
+ * @truesize: step between consecutive buffers, 0 if none exists
  * @nid: ID of the closest NUMA node with memory
  */
 struct libeth_xskfq {
@@ -614,6 +615,8 @@ struct libeth_xskfq {
 	u32			thresh;
 
 	u32			buf_len;
+	u32			truesize;
+
 	int			nid;
 };