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

[ Upstream commit 8d14768 ]

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: 2d4238f ("ice: Add support for AF_XDP")
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/net/ethernet/intel/ice/ice_xsk.c

@@ -446,8 +446,11 @@ bool ice_alloc_rx_bufs_zc(struct ice_ring *rx_ring, u16 count)
 		}
 	} while (--count);
 
-	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.status_error0 = 0;
 		ice_release_rx_desc(rx_ring, ntu);
+	}
 
 	return ret;
 }