[RFC PATCHv2 1/1] idpf: Fix header clobber in IDPF with SWIOTLB enabled

[Steve Rutherford <srutherford@google.com>]

When SWIOTLB and header split are enabled, IDPF sees empty packets in the
rx queue.

This is caused by libeth_rx_sync_for_cpu clobbering the synthesized header
in the workaround (i.e. overflow) path. After the header is synthesized by
idpf_rx_hsplit_wa, the sync call pulls from the empty SWIOTLB buffer,
effectively zeroing out the buffer.

This skips the extra sync in the workaround path in most cases. The one
exception is that it calls sync to trigger a recycle the header buffer when
it fails to find a header in the payload.

Fixes: 90912f9f4f2d1 ("idpf: convert header split mode to libeth + napi_build_skb()")
Signed-off-by: Steve Rutherford <srutherford@google.com>
---
 drivers/net/ethernet/intel/idpf/idpf_txrx.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/intel/idpf/idpf_txrx.c b/drivers/net/ethernet/intel/idpf/idpf_txrx.c
index 3ddf7b1e85ef..946203a6bd86 100644
--- a/drivers/net/ethernet/intel/idpf/idpf_txrx.c
+++ b/drivers/net/ethernet/intel/idpf/idpf_txrx.c
@@ -3007,9 +3007,14 @@ static int idpf_rx_splitq_clean(struct idpf_rx_queue *rxq, int budget)
 			u64_stats_update_begin(&rxq->stats_sync);
 			u64_stats_inc(&rxq->q_stats.hsplit_buf_ovf);
 			u64_stats_update_end(&rxq->stats_sync);
-		}
 
-		if (libeth_rx_sync_for_cpu(hdr, hdr_len)) {
+			/* Recycle the hdr buffer if unused.*/
+			if (!hdr_len)
+				libeth_rx_sync_for_cpu(hdr, 0);
+		} else if (!libeth_rx_sync_for_cpu(hdr, hdr_len))
+			hdr_len = 0;
+
+		if (hdr_len) {
 			skb = idpf_rx_build_skb(hdr, hdr_len);
 			if (!skb)
 				break;
-- 
2.53.0.473.g4a7958ca14-goog