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    Subject[PATCH 5.10 463/717] i40e, xsk: clear the status bits for the next_to_use descriptor
    Date
    From: Björn Töpel <bjorn.topel@intel.com>

    [ Upstream commit 64050b5b8706d304ba647591b06e1eddc55e8bd9 ]

    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>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/net/ethernet/intel/i40e/i40e_xsk.c | 5 ++++-
    1 file changed, 4 insertions(+), 1 deletion(-)

    diff --git a/drivers/net/ethernet/intel/i40e/i40e_xsk.c b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
    index 567fd67e900ef..e402c62eb3137 100644
    --- a/drivers/net/ethernet/intel/i40e/i40e_xsk.c
    +++ b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
    @@ -219,8 +219,11 @@ 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;
    }
    --
    2.27.0


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