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Date: Thu, 27 Jun 2019 16:18:16 +0200
From: Maciej Fijalkowski <maciejromanfijalkowski@...il.com>
To: Ilias Apalodimas <ilias.apalodimas@...aro.org>
Cc: netdev@...r.kernel.org, jaswinder.singh@...aro.org,
ard.biesheuvel@...aro.org, bjorn.topel@...el.com,
magnus.karlsson@...el.com, brouer@...hat.com, daniel@...earbox.net,
ast@...nel.org, makita.toshiaki@....ntt.co.jp,
jakub.kicinski@...ronome.com, john.fastabend@...il.com,
davem@...emloft.net
Subject: Re: [RFC, PATCH 2/2, net-next] net: netsec: add XDP support
On Tue, 25 Jun 2019 18:06:19 +0300
Ilias Apalodimas <ilias.apalodimas@...aro.org> wrote:
Hi Ilias,
> +/* The current driver only supports 1 Txq, this should run under spin_lock() */
> +static u32 netsec_xdp_queue_one(struct netsec_priv *priv,
> + struct xdp_frame *xdpf, bool is_ndo)
> +
> +{
> + struct netsec_desc_ring *tx_ring = &priv->desc_ring[NETSEC_RING_TX];
> + struct page *page = virt_to_page(xdpf->data);
> + struct netsec_tx_pkt_ctrl tx_ctrl = {};
> + struct netsec_desc tx_desc;
> + dma_addr_t dma_handle;
> + u16 filled;
> +
> + if (tx_ring->head >= tx_ring->tail)
> + filled = tx_ring->head - tx_ring->tail;
> + else
> + filled = tx_ring->head + DESC_NUM - tx_ring->tail;
> +
> + if (DESC_NUM - filled <= 1)
> + return NETSEC_XDP_CONSUMED;
> +
> + if (is_ndo) {
> + /* this is for ndo_xdp_xmit, the buffer needs mapping before
> + * sending
> + */
> + dma_handle = dma_map_single(priv->dev, xdpf->data, xdpf->len,
> + DMA_TO_DEVICE);
> + if (dma_mapping_error(priv->dev, dma_handle))
> + return NETSEC_XDP_CONSUMED;
> + tx_desc.buf_type = TYPE_NETSEC_XDP_NDO;
> + } else {
> + /* This is the device Rx buffer from page_pool. No need to remap
> + * just sync and send it
> + */
> + dma_handle = page_pool_get_dma_addr(page) +
> + NETSEC_RXBUF_HEADROOM;
> + dma_sync_single_for_device(priv->dev, dma_handle, xdpf->len,
> + DMA_BIDIRECTIONAL);
> + tx_desc.buf_type = TYPE_NETSEC_XDP_TX;
> + }
> + tx_ctrl.cksum_offload_flag = false;
> + tx_ctrl.tcp_seg_offload_flag = false;
> + tx_ctrl.tcp_seg_len = 0;
Aren't these three lines redundant? tx_ctrl is zero initialized.
> +
> + tx_desc.dma_addr = dma_handle;
> + tx_desc.addr = xdpf->data;
> + tx_desc.len = xdpf->len;
> +
> + netsec_set_tx_de(priv, tx_ring, &tx_ctrl, &tx_desc, xdpf);
> +
> + return NETSEC_XDP_TX;
> +}
> +
> +static u32 netsec_xdp_xmit_back(struct netsec_priv *priv, struct xdp_buff *xdp)
> +{
> + struct netsec_desc_ring *tx_ring = &priv->desc_ring[NETSEC_RING_TX];
> + struct xdp_frame *xdpf = convert_to_xdp_frame(xdp);
> + u32 ret;
> +
> + if (unlikely(!xdpf))
> + return NETSEC_XDP_CONSUMED;
> +
> + spin_lock(&tx_ring->lock);
> + ret = netsec_xdp_queue_one(priv, xdpf, false);
> + spin_unlock(&tx_ring->lock);
> +
> + return ret;
> +}
> +
> +static u32 netsec_run_xdp(struct netsec_priv *priv, struct bpf_prog *prog,
> + struct xdp_buff *xdp)
> +{
> + u32 ret = NETSEC_XDP_PASS;
> + int err;
> + u32 act;
> +
> + rcu_read_lock();
> + act = bpf_prog_run_xdp(prog, xdp);
> +
> + switch (act) {
> + case XDP_PASS:
> + ret = NETSEC_XDP_PASS;
> + break;
> + case XDP_TX:
> + ret = netsec_xdp_xmit_back(priv, xdp);
> + if (ret != NETSEC_XDP_TX)
> + xdp_return_buff(xdp);
> + break;
> + case XDP_REDIRECT:
> + err = xdp_do_redirect(priv->ndev, xdp, prog);
> + if (!err) {
> + ret = NETSEC_XDP_REDIR;
> + } else {
> + ret = NETSEC_XDP_CONSUMED;
> + xdp_return_buff(xdp);
> + }
> + break;
> + default:
> + bpf_warn_invalid_xdp_action(act);
> + /* fall through */
> + case XDP_ABORTED:
> + trace_xdp_exception(priv->ndev, prog, act);
> + /* fall through -- handle aborts by dropping packet */
> + case XDP_DROP:
> + ret = NETSEC_XDP_CONSUMED;
> + xdp_return_buff(xdp);
> + break;
> + }
> +
> + rcu_read_unlock();
> +
> + return ret;
> +}
> +
> static int netsec_process_rx(struct netsec_priv *priv, int budget)
> {
> struct netsec_desc_ring *dring = &priv->desc_ring[NETSEC_RING_RX];
> + struct bpf_prog *xdp_prog = READ_ONCE(priv->xdp_prog);
Reading BPF prog should be RCU protected. There might be a case where RCU
callback that destroys BPF prog is executed during the bottom half handling and
you have the PREEMPT_RCU=y in your kernel config. I've just rephrased Brenden's
words here, so for further info, see:
https://lore.kernel.org/netdev/20160904042958.8594-1-bblanco@plumgrid.com/
So either expand the RCU section or read prog pointer per each frame, under the
lock, as it seems that currently we have these two schemes in drivers that
support XDP.
> struct net_device *ndev = priv->ndev;
> struct netsec_rx_pkt_info rx_info;
> - struct sk_buff *skb;
> + struct sk_buff *skb = NULL;
> + u16 xdp_xmit = 0;
> + u32 xdp_act = 0;
> int done = 0;
>
> while (done < budget) {
> @@ -727,8 +903,10 @@ static int netsec_process_rx(struct netsec_priv *priv, int budget)
> struct netsec_de *de = dring->vaddr + (DESC_SZ * idx);
> struct netsec_desc *desc = &dring->desc[idx];
> struct page *page = virt_to_page(desc->addr);
> + u32 xdp_result = XDP_PASS;
> u16 pkt_len, desc_len;
> dma_addr_t dma_handle;
> + struct xdp_buff xdp;
> void *buf_addr;
>
> if (de->attr & (1U << NETSEC_RX_PKT_OWN_FIELD)) {
> @@ -773,7 +951,23 @@ static int netsec_process_rx(struct netsec_priv *priv, int budget)
> DMA_FROM_DEVICE);
> prefetch(desc->addr);
>
> + xdp.data_hard_start = desc->addr;
> + xdp.data = desc->addr + NETSEC_RXBUF_HEADROOM;
> + xdp_set_data_meta_invalid(&xdp);
> + xdp.data_end = xdp.data + pkt_len;
> + xdp.rxq = &dring->xdp_rxq;
> +
> + if (xdp_prog) {
> + xdp_result = netsec_run_xdp(priv, xdp_prog, &xdp);
> + if (xdp_result != NETSEC_XDP_PASS) {
> + xdp_act |= xdp_result;
> + if (xdp_result == NETSEC_XDP_TX)
> + xdp_xmit++;
> + goto next;
> + }
> + }
> skb = build_skb(desc->addr, desc->len + NETSEC_RX_BUF_NON_DATA);
> +
> if (unlikely(!skb)) {
> /* If skb fails recycle_direct will either unmap and
> * free the page or refill the cache depending on the
> @@ -787,27 +981,30 @@ static int netsec_process_rx(struct netsec_priv *priv, int budget)
> }
> page_pool_release_page(dring->page_pool, page);
>
> - /* Update the descriptor with the new buffer we allocated */
> - desc->len = desc_len;
> - desc->dma_addr = dma_handle;
> - desc->addr = buf_addr;
> -
> - skb_reserve(skb, NETSEC_SKB_PAD);
> - skb_put(skb, pkt_len);
> + skb_reserve(skb, xdp.data - xdp.data_hard_start);
> + skb_put(skb, xdp.data_end - xdp.data);
> skb->protocol = eth_type_trans(skb, priv->ndev);
>
> if (priv->rx_cksum_offload_flag &&
> rx_info.rx_cksum_result == NETSEC_RX_CKSUM_OK)
> skb->ip_summed = CHECKSUM_UNNECESSARY;
>
> - if (napi_gro_receive(&priv->napi, skb) != GRO_DROP) {
> +next:
> + if ((skb && napi_gro_receive(&priv->napi, skb) != GRO_DROP) ||
> + xdp_result & NETSEC_XDP_RX_OK) {
> ndev->stats.rx_packets++;
> - ndev->stats.rx_bytes += pkt_len;
> + ndev->stats.rx_bytes += xdp.data_end - xdp.data;
> }
>
> + /* Update the descriptor with fresh buffers */
> + desc->len = desc_len;
> + desc->dma_addr = dma_handle;
> + desc->addr = buf_addr;
> +
> netsec_rx_fill(priv, idx, 1);
> dring->tail = (dring->tail + 1) % DESC_NUM;
> }
> + netsec_finalize_xdp_rx(priv, xdp_act, xdp_xmit);
>
> return done;
> }
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