netdev - Re: [PATCH v9 net-next 3/4] xdp: add multi-buff support for xdp running in generic mode

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Date: Sat, 17 Feb 2024 12:07:01 +0200
From: Julian Wiedmann <jwiedmann.dev@...il.com>
To: Lorenzo Bianconi <lorenzo@...nel.org>, netdev@...r.kernel.org
Cc: lorenzo.bianconi@...hat.com, kuba@...nel.org, davem@...emloft.net,
 edumazet@...gle.com, pabeni@...hat.com, bpf@...r.kernel.org,
 toke@...hat.com, willemdebruijn.kernel@...il.com, jasowang@...hat.com,
 sdf@...gle.com, hawk@...nel.org, ilias.apalodimas@...aro.org,
 linyunsheng@...wei.com
Subject: Re: [PATCH v9 net-next 3/4] xdp: add multi-buff support for xdp
 running in generic mode



On 12.02.24 11:50, Lorenzo Bianconi wrote:
> Similar to native xdp, do not always linearize the skb in
> netif_receive_generic_xdp routine but create a non-linear xdp_buff to be
> processed by the eBPF program. This allow to add multi-buffer support
> for xdp running in generic mode.
> 
> Acked-by: Jesper Dangaard Brouer <hawk@...nel.org>
> Reviewed-by: Toke Hoiland-Jorgensen <toke@...hat.com>
> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> ---
>  include/linux/skbuff.h |  2 +
>  net/core/dev.c         | 70 +++++++++++++++++++++++---------
>  net/core/skbuff.c      | 91 ++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 144 insertions(+), 19 deletions(-)
> 

[...]

> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 9e5eb47b4025..bdb94749f05d 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -895,6 +895,97 @@ static bool is_pp_page(struct page *page)
>  	return (page->pp_magic & ~0x3UL) == PP_SIGNATURE;
>  }
>  
> +static int skb_pp_cow_data(struct page_pool *pool, struct sk_buff **pskb,
> +			   unsigned int headroom)
> +{
> +#if IS_ENABLED(CONFIG_PAGE_POOL)
> +	u32 size, truesize, len, max_head_size, off;
> +	struct sk_buff *skb = *pskb, *nskb;
> +	int err, i, head_off;
> +	void *data;
> +
> +	/* XDP does not support fraglist so we need to linearize
> +	 * the skb.
> +	 */
> +	if (skb_has_frag_list(skb))
> +		return -EOPNOTSUPP;
> +
> +	max_head_size = SKB_WITH_OVERHEAD(PAGE_SIZE - headroom);
> +	if (skb->len > max_head_size + MAX_SKB_FRAGS * PAGE_SIZE)
> +		return -ENOMEM;
> +
> +	size = min_t(u32, skb->len, max_head_size);
> +	truesize = SKB_HEAD_ALIGN(size) + headroom;
> +	data = page_pool_dev_alloc_va(pool, &truesize);
> +	if (!data)
> +		return -ENOMEM;
> +
> +	nskb = napi_build_skb(data, truesize);
> +	if (!nskb) {
> +		page_pool_free_va(pool, data, true);
> +		return -ENOMEM;
> +	}
> +
> +	skb_reserve(nskb, headroom);
> +	skb_copy_header(nskb, skb);
> +	skb_mark_for_recycle(nskb);
> +
> +	err = skb_copy_bits(skb, 0, nskb->data, size);
> +	if (err) {
> +		consume_skb(nskb);
> +		return err;
> +	}
> +	skb_put(nskb, size);
> +
> +	head_off = skb_headroom(nskb) - skb_headroom(skb);
> +	skb_headers_offset_update(nskb, head_off);
> +
> +	off = size;
> +	len = skb->len - off;
> +	for (i = 0; i < MAX_SKB_FRAGS && off < skb->len; i++) {
> +		struct page *page;
> +		u32 page_off;
> +
> +		size = min_t(u32, len, PAGE_SIZE);
> +		truesize = size;
> +
> +		page = page_pool_dev_alloc(pool, &page_off, &truesize);
> +		if (!data) {
> +			consume_skb(nskb);
> +			return -ENOMEM;
> +		}
> +

This should check for !page instead, no?

(picked up as CID 1583654 by the coverity scan for linux-next)