i40e, xsk: clear the status bits for the next_to_use descriptor

On the Rx side, the next_to_use index points to the next item in the
HW ring to be refilled/allocated, and next_to_clean points to the next
item to potentially be processed.

When the HW Rx ring is fully refilled, i.e. no packets has been
processed, the next_to_use will be next_to_clean - 1. When the ring is
fully processed next_to_clean will be equal to next_to_use. The latter
case is where a bug is triggered.

If the next_to_use bits are not cleared, and the "fully processed"
state is entered, a stale descriptor can be processed.

The skb-path correctly clear the status bit for the next_to_use
descriptor, but the AF_XDP zero-copy path did not do that.

This change adds the status bits clearing of the next_to_use
descriptor.

Fixes: 3b4f0b66c2b3 ("i40e, xsk: Migrate to new MEM_TYPE_XSK_BUFF_POOL")
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/ethernet/intel/i40e/i40e_xsk.c b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
index bfa84bf..47eb9c5 100644 (file)
--- a/drivers/net/ethernet/intel/i40e/i40e_xsk.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
@@ -220,8 +220,11 @@ bool i40e_alloc_rx_buffers_zc(struct i40e_ring *rx_ring, u16 count)
        } while (count);
 
 no_buffers:
-       if (rx_ring->next_to_use != ntu)
+       if (rx_ring->next_to_use != ntu) {
+               /* clear the status bits for the next_to_use descriptor */
+               rx_desc->wb.qword1.status_error_len = 0;
                i40e_release_rx_desc(rx_ring, ntu);
+       }
 
        return ok;
 }