linux-kernel - Re: [PATCH net-next v2 4/6] net: stmmac: Add initial XDP support

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Date:   Tue, 30 Mar 2021 19:42:15 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Ong Boon Leong <boon.leong.ong@...el.com>
Cc:     Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Jose Abreu <joabreu@...opsys.com>,
        "David S . Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>, netdev@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH net-next v2 4/6] net: stmmac: Add initial XDP support

On Tue, 30 Mar 2021 10:49:47 +0800 Ong Boon Leong wrote:
> +		if (!skb) {
> +			dma_sync_single_for_cpu(priv->device, buf->addr,
> +						buf1_len, dma_dir);
> +
> +			xdp.data = page_address(buf->page) + buf->page_offset;
> +			xdp.data_end = xdp.data + len;
> +			xdp.data_hard_start = page_address(buf->page);
> +			xdp_set_data_meta_invalid(&xdp);
> +			xdp.frame_sz = buf_sz;
> +
> +			skb = stmmac_xdp_run_prog(priv, &xdp);
> +
> +			/* For Not XDP_PASS verdict */
> +			if (IS_ERR(skb)) {
> +				unsigned int xdp_res = -PTR_ERR(skb);
> +
> +				if (xdp_res & STMMAC_XDP_CONSUMED) {
> +					page_pool_recycle_direct(rx_q->page_pool,
> +								 buf->page);
> +					buf->page = NULL;
> +					priv->dev->stats.rx_dropped++;
> +
> +					/* Clear skb as it was set as
> +					 * status by XDP program.
> +					 */
> +					skb = NULL;
> +
> +					if (unlikely((status & rx_not_ls)))
> +						goto read_again;
> +
> +					count++;
> +					continue;
> +				}
> +			}
> +		}
> +
>  		if (!skb) {
>  			skb = napi_alloc_skb(&ch->rx_napi, buf1_len);
>  			if (!skb) {
> @@ -4322,9 +4400,8 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
>  				goto drain_data;
>  			}
>  
> -			dma_sync_single_for_cpu(priv->device, buf->addr,
> -						buf1_len, DMA_FROM_DEVICE);
> -			skb_copy_to_linear_data(skb, page_address(buf->page),
> +			skb_copy_to_linear_data(skb, page_address(buf->page) +
> +						buf->page_offset,
>  						buf1_len);

XDP can prepend or remove headers (using the bpf_xdp_adjust_head()
helper), so the start of data may no longer be page + HEADROOM, 
and the length of the frame may have changed. 

Are you accounting for this?