netdev - Re: [PATCH v3 bpf-next 2/8] veth: Add driver XDP

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Date:   Tue, 24 Jul 2018 10:47:25 +0900
From:   Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Toshiaki Makita <toshiaki.makita1@...il.com>
Cc:     netdev@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [PATCH v3 bpf-next 2/8] veth: Add driver XDP

Hi Jakub,

Thanks for reviewing!

On 2018/07/24 9:23, Jakub Kicinski wrote:
> On Mon, 23 Jul 2018 00:13:02 +0900, Toshiaki Makita wrote:
>> From: Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
>>
>> This is the basic implementation of veth driver XDP.
>>
>> Incoming packets are sent from the peer veth device in the form of skb,
>> so this is generally doing the same thing as generic XDP.
>>
>> This itself is not so useful, but a starting point to implement other
>> useful veth XDP features like TX and REDIRECT.
>>
>> This introduces NAPI when XDP is enabled, because XDP is now heavily
>> relies on NAPI context. Use ptr_ring to emulate NIC ring. Tx function
>> enqueues packets to the ring and peer NAPI handler drains the ring.
>>
>> Currently only one ring is allocated for each veth device, so it does
>> not scale on multiqueue env. This can be resolved by allocating rings
>> on the per-queue basis later.
>>
>> Note that NAPI is not used but netif_rx is used when XDP is not loaded,
>> so this does not change the default behaviour.
>>
>> v3:
>> - Fix race on closing the device.
>> - Add extack messages in ndo_bpf.
>>
>> v2:
>> - Squashed with the patch adding NAPI.
>> - Implement adjust_tail.
>> - Don't acquire consumer lock because it is guarded by NAPI.
>> - Make poll_controller noop since it is unnecessary.
>> - Register rxq_info on enabling XDP rather than on opening the device.
>>
>> Signed-off-by: Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
> 
>> +static struct sk_buff *veth_xdp_rcv_skb(struct veth_priv *priv,
>> +					struct sk_buff *skb)
>> +{
>> +	u32 pktlen, headroom, act, metalen;
>> +	void *orig_data, *orig_data_end;
>> +	int size, mac_len, delta, off;
>> +	struct bpf_prog *xdp_prog;
>> +	struct xdp_buff xdp;
>> +
>> +	rcu_read_lock();
>> +	xdp_prog = rcu_dereference(priv->xdp_prog);
>> +	if (unlikely(!xdp_prog)) {
>> +		rcu_read_unlock();
>> +		goto out;
>> +	}
>> +
>> +	mac_len = skb->data - skb_mac_header(skb);
>> +	pktlen = skb->len + mac_len;
>> +	size = SKB_DATA_ALIGN(VETH_XDP_HEADROOM + pktlen) +
>> +	       SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
>> +	if (size > PAGE_SIZE)
>> +		goto drop;
>> +
>> +	headroom = skb_headroom(skb) - mac_len;
>> +	if (skb_shared(skb) || skb_head_is_locked(skb) ||
>> +	    skb_is_nonlinear(skb) || headroom < XDP_PACKET_HEADROOM) {
>> +		struct sk_buff *nskb;
>> +		void *head, *start;
>> +		struct page *page;
>> +		int head_off;
>> +
>> +		page = alloc_page(GFP_ATOMIC);
>> +		if (!page)
>> +			goto drop;
>> +
>> +		head = page_address(page);
>> +		start = head + VETH_XDP_HEADROOM;
>> +		if (skb_copy_bits(skb, -mac_len, start, pktlen)) {
>> +			page_frag_free(head);
>> +			goto drop;
>> +		}
>> +
>> +		nskb = veth_build_skb(head,
>> +				      VETH_XDP_HEADROOM + mac_len, skb->len,
>> +				      PAGE_SIZE);
>> +		if (!nskb) {
>> +			page_frag_free(head);
>> +			goto drop;
>> +		}
> 
>> +static int veth_enable_xdp(struct net_device *dev)
>> +{
>> +	struct veth_priv *priv = netdev_priv(dev);
>> +	int err;
>> +
>> +	if (!xdp_rxq_info_is_reg(&priv->xdp_rxq)) {
>> +		err = xdp_rxq_info_reg(&priv->xdp_rxq, dev, 0);
>> +		if (err < 0)
>> +			return err;
>> +
>> +		err = xdp_rxq_info_reg_mem_model(&priv->xdp_rxq,
>> +						 MEM_TYPE_PAGE_SHARED, NULL);
> 
> nit: doesn't matter much but looks like a mix of MEM_TYPE_PAGE_SHARED
>      and MEM_TYPE_PAGE_ORDER0

Actually I'm not sure when to use MEM_TYPE_PAGE_ORDER0. It seems a page
allocated by alloc_page() can be freed by page_frag_free() and it is
more lightweight than put_page(), isn't it?
virtio_net is doing it in a similar way.

-- 
Toshiaki Makita