On Wed, 3 Mar 2021 16:39:26 +0100
Maciej Fijalkowski <maciej.fijalkowski@xxxxxxxxx> wrote:
> i40e_rx_offset(), that is supposed to initialize the Rx buffer headroom,
> relies on I40E_RXR_FLAGS_BUILD_SKB_ENABLED flag.
>
> Currently, the callsite of mentioned function is placed incorrectly
> within i40e_setup_rx_descriptors() where Rx ring's build skb flag is not
> set yet. This causes the XDP_REDIRECT to be partially broken due to
> inability to create xdp_frame in the headroom space, as the headroom is
> 0.
>
> For the record, below is the call graph:
>
> i40e_vsi_open
> i40e_vsi_setup_rx_resources
> i40e_setup_rx_descriptors
> i40e_rx_offset() <-- sets offset to 0 as build_skb flag is set below
>
> i40e_vsi_configure_rx
> i40e_configure_rx_ring
> set_ring_build_skb_enabled(ring) <-- set build_skb flag
>
> Fix this by moving i40e_rx_offset() to i40e_configure_rx_ring() after
> the flag setting.
>
> Fixes: f7bb0d71d658 ("i40e: store the result of i40e_rx_offset() onto i40e_ring")
> Reported-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
> Co-developed-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
> Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
> Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@xxxxxxxxx>
> ---
> drivers/net/ethernet/intel/i40e/i40e_main.c | 13 +++++++++++++
> drivers/net/ethernet/intel/i40e/i40e_txrx.c | 12 ------------
> 2 files changed, 13 insertions(+), 12 deletions(-)
Acked-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
Tested-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
I'm currently looking at extending samples/bpf/ xdp_redirect_map to
detect the situation. As with this bug the redirect tests/sample
programs will just report really high performance numbers (because
packets are dropped earlier due to err). Knowing what performance
numbers to expect, I could see that they were out-of-spec, and
investigated the root-cause.
I assume Intel QA tested XDP-redirect and didn't find the bug due to
this. Red Hat QA also use samples/bpf/xdp* and based on the reports I
get from them, I could not blame them if this bug would slip through,
as the tool reports "good" results.
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
