[xdp-hints] Re: [PATCH bpf-next v6 07/18] ice: Support XDP hints in AF_XDP ZC mode

[Maciej Fijalkowski <maciej.fijalkowski@intel.com>]

On Thu, Oct 12, 2023 at 07:05:13PM +0200, Larysa Zaremba wrote:
> In AF_XDP ZC, xdp_buff is not stored on ring,
> instead it is provided by xsk_buff_pool.
> Space for metadata sources right after such buffers was already reserved
> in commit 94ecc5ca4dbf ("xsk: Add cb area to struct xdp_buff_xsk").
> This makes the implementation rather straightforward.
> 
> Update AF_XDP ZC packet processing to support XDP hints.
> 
> Signed-off-by: Larysa Zaremba <larysa.zaremba@intel.com>
> ---
>  drivers/net/ethernet/intel/ice/ice_xsk.c | 34 ++++++++++++++++++++++--
>  1 file changed, 32 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/ice/ice_xsk.c b/drivers/net/ethernet/intel/ice/ice_xsk.c
> index ef778b8e6d1b..6ca620b2fbdd 100644
> --- a/drivers/net/ethernet/intel/ice/ice_xsk.c
> +++ b/drivers/net/ethernet/intel/ice/ice_xsk.c
> @@ -752,22 +752,51 @@ static int ice_xmit_xdp_tx_zc(struct xdp_buff *xdp,
>  	return ICE_XDP_CONSUMED;
>  }
>  
> +/**
> + * ice_prepare_pkt_ctx_zc - Prepare packet context for XDP hints
> + * @xdp: xdp_buff used as input to the XDP program
> + * @eop_desc: End of packet descriptor
> + * @rx_ring: Rx ring with packet context
> + *
> + * In regular XDP, xdp_buff is placed inside the ring structure,
> + * just before the packet context, so the latter can be accessed
> + * with xdp_buff address only at all times, but in ZC mode,

s/only// ?

> + * xdp_buffs come from the pool, so we need to reinitialize
> + * context for every packet.
> + *
> + * We can safely convert xdp_buff_xsk to ice_xdp_buff,
> + * because there are XSK_PRIV_MAX bytes reserved in xdp_buff_xsk
> + * right after xdp_buff, for our private use.
> + * XSK_CHECK_PRIV_TYPE() ensures we do not go above the limit.
> + */
> +static void ice_prepare_pkt_ctx_zc(struct xdp_buff *xdp,
> +				   union ice_32b_rx_flex_desc *eop_desc,
> +				   struct ice_rx_ring *rx_ring)
> +{
> +	XSK_CHECK_PRIV_TYPE(struct ice_xdp_buff);
> +	((struct ice_xdp_buff *)xdp)->pkt_ctx = rx_ring->pkt_ctx;
> +	ice_xdp_meta_set_desc(xdp, eop_desc);
> +}
> +
>  /**
>   * ice_run_xdp_zc - Executes an XDP program in zero-copy path
>   * @rx_ring: Rx ring
>   * @xdp: xdp_buff used as input to the XDP program
>   * @xdp_prog: XDP program to run
>   * @xdp_ring: ring to be used for XDP_TX action
> + * @rx_desc: packet descriptor
>   *
>   * Returns any of ICE_XDP_{PASS, CONSUMED, TX, REDIR}
>   */
>  static int
>  ice_run_xdp_zc(struct ice_rx_ring *rx_ring, struct xdp_buff *xdp,
> -	       struct bpf_prog *xdp_prog, struct ice_tx_ring *xdp_ring)
> +	       struct bpf_prog *xdp_prog, struct ice_tx_ring *xdp_ring,
> +	       union ice_32b_rx_flex_desc *rx_desc)
>  {
>  	int err, result = ICE_XDP_PASS;
>  	u32 act;
>  
> +	ice_prepare_pkt_ctx_zc(xdp, rx_desc, rx_ring);
>  	act = bpf_prog_run_xdp(xdp_prog, xdp);
>  
>  	if (likely(act == XDP_REDIRECT)) {
> @@ -907,7 +936,8 @@ int ice_clean_rx_irq_zc(struct ice_rx_ring *rx_ring, int budget)
>  		if (ice_is_non_eop(rx_ring, rx_desc))
>  			continue;
>  
> -		xdp_res = ice_run_xdp_zc(rx_ring, first, xdp_prog, xdp_ring);
> +		xdp_res = ice_run_xdp_zc(rx_ring, first, xdp_prog, xdp_ring,
> +					 rx_desc);
>  		if (likely(xdp_res & (ICE_XDP_TX | ICE_XDP_REDIR))) {
>  			xdp_xmit |= xdp_res;
>  		} else if (xdp_res == ICE_XDP_EXIT) {
> -- 
> 2.41.0
>