[PATCH v2 3/9] net/gve: copy data to QPL buffer when mbuf read does not

[Joshua Washington <joshwash@google.com>]

The rte_pktmbuf_read method does not guarantee that data will be copied
from an mbuf. If the requested data is all contiguous, the method will
instead return a pointer to the memory location within the buffer that
should be read from, leaving the destination buffer empty.

This is problematic for TSO/multi-segment TX packets which only make use
of two mbufs. If all data in the second mbuf is contiguous, the data
will not be read to QPL memory.

Update the QPL copy logic to copy if the rte_pktmbuf_read does not.

Fixes: a46583cf43c8 ("net/gve: support Rx/Tx")
Cc: stable@dpdk.org
Signed-off-by: Joshua Washington <joshwash@google.com>
Reviewed-by: Jasper Tran O'Leary <jtranoleary@google.com>
---
v2:
  Removed unused declaration and definition of addr

 drivers/net/gve/gve_tx.c | 38 +++++++++++++++++++++++---------------
 1 file changed, 23 insertions(+), 15 deletions(-)

diff --git a/drivers/net/gve/gve_tx.c b/drivers/net/gve/gve_tx.c
index 59c82b04ed..d220d5167a 100644
--- a/drivers/net/gve/gve_tx.c
+++ b/drivers/net/gve/gve_tx.c
@@ -255,10 +255,10 @@ gve_tx_burst_qpl(void *tx_queue, struct rte_mbuf **tx_pkts, uint16_t nb_pkts)
 	struct rte_mbuf **sw_ring = txq->sw_ring;
 	uint16_t mask = txq->nb_tx_desc - 1;
 	uint16_t tx_id = txq->tx_tail & mask;
-	uint64_t ol_flags, addr, fifo_addr;
 	uint32_t tx_tail = txq->tx_tail;
 	struct rte_mbuf *tx_pkt, *first;
 	uint16_t sw_id = txq->sw_tail;
+	uint64_t ol_flags, fifo_addr;
 	uint16_t nb_used, i;
 	uint64_t bytes = 0;
 	uint16_t nb_tx = 0;
@@ -273,6 +273,9 @@ gve_tx_burst_qpl(void *tx_queue, struct rte_mbuf **tx_pkts, uint16_t nb_pkts)
 		gve_tx_clean_swr_qpl(txq);

 	for (nb_tx = 0; nb_tx < nb_pkts; nb_tx++) {
+		const void *mbuf_header_addr;
+		void *qpl_write_addr;
+
 		tx_pkt = *tx_pkts++;
 		ol_flags = tx_pkt->ol_flags;

@@ -306,7 +309,6 @@ gve_tx_burst_qpl(void *tx_queue, struct rte_mbuf **tx_pkts, uint16_t nb_pkts)
 			if (!is_fifo_avail(txq, hlen))
 				goto end_of_tx;
 		}
-		addr = (uint64_t)(tx_pkt->buf_addr) + tx_pkt->data_off;
 		fifo_addr = gve_tx_alloc_from_fifo(txq, tx_id, hlen);

 		/* For TSO, check if there's enough fifo space for data first */
@@ -317,26 +319,32 @@ gve_tx_burst_qpl(void *tx_queue, struct rte_mbuf **tx_pkts, uint16_t nb_pkts)
 					goto end_of_tx;
 			}
 		}
-		if (tx_pkt->nb_segs == 1 || ol_flags & RTE_MBUF_F_TX_TCP_SEG)
-			rte_memcpy((void *)(size_t)(fifo_addr + txq->fifo_base),
-				   (void *)(size_t)addr, hlen);
-		else
-			rte_pktmbuf_read(tx_pkt, 0, hlen,
-					 (void *)(size_t)(fifo_addr + txq->fifo_base));
+
+		qpl_write_addr = (void *)(size_t)(fifo_addr + txq->fifo_base);
+		mbuf_header_addr = rte_pktmbuf_read(tx_pkt, 0, hlen, qpl_write_addr);
+
+		/* Header data is linear in the mbuf head. Copy directly. */
+		if (mbuf_header_addr != qpl_write_addr)
+			rte_memcpy(qpl_write_addr, mbuf_header_addr, hlen);
+
 		gve_tx_fill_pkt_desc(txd, tx_pkt, nb_used, hlen, fifo_addr);

 		if (ol_flags & RTE_MBUF_F_TX_TCP_SEG) {
+			const void *mbuf_payload_addr;
+
 			tx_id = (tx_id + 1) & mask;
 			txd = &txr[tx_id];
-			addr = (uint64_t)(tx_pkt->buf_addr) + tx_pkt->data_off + hlen;
 			fifo_addr = gve_tx_alloc_from_fifo(txq, tx_id, tx_pkt->pkt_len - hlen);
-			if (tx_pkt->nb_segs == 1)
-				rte_memcpy((void *)(size_t)(fifo_addr + txq->fifo_base),
-					   (void *)(size_t)addr,
+			qpl_write_addr = (void *)(txq->fifo_base + fifo_addr);
+			mbuf_payload_addr = rte_pktmbuf_read(tx_pkt, hlen, tx_pkt->pkt_len - hlen,
+							     qpl_write_addr);
+
+			/* Payload data is contiguous. Take the offset from the
+			 * read request and copy from there.
+			 */
+			if (mbuf_payload_addr != qpl_write_addr)
+				rte_memcpy(qpl_write_addr, mbuf_payload_addr,
 					   tx_pkt->pkt_len - hlen);
-			else
-				rte_pktmbuf_read(tx_pkt, hlen, tx_pkt->pkt_len - hlen,
-						 (void *)(size_t)(fifo_addr + txq->fifo_base));

 			gve_tx_fill_seg_desc(txd, ol_flags, tx_offload,
 					     tx_pkt->pkt_len - hlen, fifo_addr);
--
2.55.0.rc0.799.gd6f94ed593-goog