netdev - Re: [PATCH net 1/1] ice: xsk: do not use xdp_return_frame() on tx_buf->raw

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Date:   Wed, 21 Dec 2022 09:09:30 +0100
From:   Piotr Raczynski <piotr.raczynski@...el.com>
To:     Tony Nguyen <anthony.l.nguyen@...el.com>
CC:     <davem@...emloft.net>, <kuba@...nel.org>, <pabeni@...hat.com>,
        <edumazet@...gle.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        <netdev@...r.kernel.org>, <magnus.karlsson@...el.com>,
        <ast@...nel.org>, <daniel@...earbox.net>, <hawk@...nel.org>,
        <john.fastabend@...il.com>, <bpf@...r.kernel.org>,
        Robin Cowley <robin.cowley@...hutgroup.com>,
        "Chandan Kumar Rout" <chandanx.rout@...el.com>
Subject: Re: [PATCH net 1/1] ice: xsk: do not use xdp_return_frame() on
 tx_buf->raw_buf

On Tue, Dec 20, 2022 at 09:54:48AM -0800, Tony Nguyen wrote:
> From: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
> 
> Previously ice XDP xmit routine was changed in a way that it avoids
> xdp_buff->xdp_frame conversion as it is simply not needed for handling
> XDP_TX action and what is more it saves us CPU cycles. This routine is
> re-used on ZC driver to handle XDP_TX action.
> 
> Although for XDP_TX on Rx ZC xdp_buff that comes from xsk_buff_pool is
> converted to xdp_frame, xdp_frame itself is not stored inside
> ice_tx_buf, we only store raw data pointer. Casting this pointer to
> xdp_frame and calling against it xdp_return_frame in
> ice_clean_xdp_tx_buf() results in undefined behavior.
> 
> To fix this, simply call page_frag_free() on tx_buf->raw_buf.
> Later intention is to remove the buff->frame conversion in order to
> simplify the codebase and improve XDP_TX performance on ZC.
> 
> Fixes: 126cdfe1007a ("ice: xsk: Improve AF_XDP ZC Tx and use batching API")
> Reported-and-tested-by: Robin Cowley <robin.cowley@...hutgroup.com>
> Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
> Tested-by: Chandan Kumar Rout <chandanx.rout@...el.com> (A Contingent Worker at Intel)
> Signed-off-by: Tony Nguyen <anthony.l.nguyen@...el.com>
> ---
>  drivers/net/ethernet/intel/ice/ice_xsk.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/intel/ice/ice_xsk.c b/drivers/net/ethernet/intel/ice/ice_xsk.c
> index 907055b77af0..7105de6fb344 100644
> --- a/drivers/net/ethernet/intel/ice/ice_xsk.c
> +++ b/drivers/net/ethernet/intel/ice/ice_xsk.c
> @@ -783,7 +783,7 @@ int ice_clean_rx_irq_zc(struct ice_rx_ring *rx_ring, int budget)
>  static void
>  ice_clean_xdp_tx_buf(struct ice_tx_ring *xdp_ring, struct ice_tx_buf *tx_buf)
>  {
> -	xdp_return_frame((struct xdp_frame *)tx_buf->raw_buf);
> +	page_frag_free(tx_buf->raw_buf);
>  	xdp_ring->xdp_tx_active--;
>  	dma_unmap_single(xdp_ring->dev, dma_unmap_addr(tx_buf, dma),
>  			 dma_unmap_len(tx_buf, len), DMA_TO_DEVICE);
> -- 
> 2.35.1
> 
LGTM

Reviewed-by: Piotr Raczynski <piotr.raczynski@...tel.com>