RE: [EXT] Re: [PATCH 1/1] net: fec: add initial XDP support

Shenwei Wang
2022-09-29T13:11:07Z

> -----Original Message-----
> From: Jesper Dangaard Brouer <jbrouer@redhat.com>
> Sent: Thursday, September 29, 2022 5:17 AM
> To: Shenwei Wang <shenwei.wang@nxp.com>; Joakim Zhang
> <qiangqing.zhang@nxp.com>; David S. Miller <davem@davemloft.net>; Eric
> Dumazet <edumazet@google.com>; Jakub Kicinski <kuba@kernel.org>; Paolo
> Abeni <pabeni@redhat.com>
> > diff --git a/drivers/net/ethernet/freescale/fec.h
> > b/drivers/net/ethernet/freescale/fec.h
> > index b0100fe3c9e4..f7531503aa95 100644
> > --- a/drivers/net/ethernet/freescale/fec.h
> > +++ b/drivers/net/ethernet/freescale/fec.h
> > @@ -346,8 +346,10 @@ struct bufdesc_ex {
> > * the skbuffer directly.
> > */
> >
> > +#define FEC_ENET_XDP_HEADROOM (512) /* XDP_PACKET_HEADROOM
> + NET_IP_ALIGN) */
>
> Why the large headroom?
>

The accurate value here should be "XDP_PACKET_HEADROOM (256) + NET_IP_ALIGN" which then aligns with 64 bytes. So 256 + 64 should be enough here.

> > +
> > #define FEC_ENET_RX_PAGES 256
> > -#define FEC_ENET_RX_FRSIZE 2048
> > +#define FEC_ENET_RX_FRSIZE (PAGE_SIZE - FEC_ENET_XDP_HEADROOM)
>
> This FEC_ENET_RX_FRSIZE is likely wrong, because you also need to reserve 320
> bytes at the end for struct skb_shared_info.
> (320 calculated as SKB_DATA_ALIGN(sizeof(struct skb_shared_info)))
>
> > #define FEC_ENET_RX_FRPPG (PAGE_SIZE / FEC_ENET_RX_FRSIZE)
> > #define RX_RING_SIZE (FEC_ENET_RX_FRPPG *
> FEC_ENET_RX_PAGES)
> > #define FEC_ENET_TX_FRSIZE 2048
> > @@ -517,6 +519,22 @@ struct bufdesc_prop {
> [...]
>
> > diff --git a/drivers/net/ethernet/freescale/fec_main.c
> > b/drivers/net/ethernet/freescale/fec_main.c
> > index 59921218a8a4..2e30182ed770 100644
> > --- a/drivers/net/ethernet/freescale/fec_main.c
> > +++ b/drivers/net/ethernet/freescale/fec_main.c
> > @@ -66,6 +66,8 @@
> > #include <linux/mfd/syscon.h>
> > #include <linux/regmap.h>
> > #include <soc/imx/cpuidle.h>
> > +#include <linux/filter.h>
> > +#include <linux/bpf.h>
> >
> > #include <asm/cacheflush.h>
> >
> > @@ -87,6 +89,11 @@ static const u16 fec_enet_vlan_pri_to_queue[8] = {0, 0,
> 1, 1, 1, 2, 2, 2};
> > #define FEC_ENET_OPD_V 0xFFF0
> > #define FEC_MDIO_PM_TIMEOUT 100 /* ms */
> >
> > +#define FEC_ENET_XDP_PASS 0
> > +#define FEC_ENET_XDP_CONSUMED BIT(0)
> > +#define FEC_ENET_XDP_TX BIT(1)
> > +#define FEC_ENET_XDP_REDIR BIT(2)
> > +
> > struct fec_devinfo {
> > u32 quirks;
> > };
> > @@ -422,6 +429,49 @@ fec_enet_clear_csum(struct sk_buff *skb, struct
> net_device *ndev)
> > return 0;
> > }
> >
> > +static int
> > +fec_enet_create_page_pool(struct fec_enet_private *fep,
> > + struct fec_enet_priv_rx_q *rxq, int size) {
> > + struct bpf_prog *xdp_prog = READ_ONCE(fep->xdp_prog);
> > + struct page_pool_params pp_params = {
> > + .order = 0,
> > + .flags = PP_FLAG_DMA_MAP | PP_FLAG_DMA_SYNC_DEV,
> > + .pool_size = size,
> > + .nid = dev_to_node(&fep->pdev->dev),
> > + .dev = &fep->pdev->dev,
> > + .dma_dir = xdp_prog ? DMA_BIDIRECTIONAL : DMA_FROM_DEVICE,
> > + .offset = FEC_ENET_XDP_HEADROOM,
> > + .max_len = FEC_ENET_RX_FRSIZE,
>
> XDP BPF-prog cannot access last 320 bytes, so FEC_ENET_RX_FRSIZE is wrong
> here.
>

So the FEC_ENET_RX_FRSIZE should subtract the sizeof(struct skb_shared_info) in the definition, right?

> > + };
> > + int err;
> > +
> > + rxq->page_pool = page_pool_create(&pp_params);
> > + if (IS_ERR(rxq->page_pool)) {
> > + err = PTR_ERR(rxq->page_pool);
> > + rxq->page_pool = NULL;
> > + return err;
> > + }
> > +
> > + err = xdp_rxq_info_reg(&rxq->xdp_rxq, fep->netdev, rxq->id, 0);
> > + if (err < 0)
> > + goto err_free_pp;
> > +
> > + err = xdp_rxq_info_reg_mem_model(&rxq->xdp_rxq,
> MEM_TYPE_PAGE_POOL,
> > + rxq->page_pool);
> > + if (err)
> > + goto err_unregister_rxq;
> > +
> > + return 0;
> > +
> > +err_unregister_rxq:
> > + xdp_rxq_info_unreg(&rxq->xdp_rxq);
> > +err_free_pp:
> > + page_pool_destroy(rxq->page_pool);
> > + rxq->page_pool = NULL;
> > + return err;
> > +}
> > +
> > static struct bufdesc *
> > fec_enet_txq_submit_frag_skb(struct fec_enet_priv_tx_q *txq,
> > struct sk_buff *skb, @@ -1285,7 +1335,6 @@
> > fec_stop(struct net_device *ndev)
> > }
> > }
> >
> > -
> > static void
> > fec_timeout(struct net_device *ndev, unsigned int txqueue)
> > {
> > @@ -1450,7 +1499,7 @@ static void fec_enet_tx(struct net_device *ndev)
> > fec_enet_tx_queue(ndev, i);
> > }
> >
> > -static int
> > +static int __maybe_unused
> > fec_enet_new_rxbdp(struct net_device *ndev, struct bufdesc *bdp, struct
> sk_buff *skb)
> > {
> > struct fec_enet_private *fep = netdev_priv(ndev); @@ -1470,8
> > +1519,9 @@ fec_enet_new_rxbdp(struct net_device *ndev, struct bufdesc
> *bdp, struct sk_buff
> > return 0;
> > }
> >
> > -static bool fec_enet_copybreak(struct net_device *ndev, struct sk_buff **skb,
> > - struct bufdesc *bdp, u32 length, bool swap)
> > +static bool __maybe_unused
> > +fec_enet_copybreak(struct net_device *ndev, struct sk_buff **skb,
> > + struct bufdesc *bdp, u32 length, bool swap)
> > {
> > struct fec_enet_private *fep = netdev_priv(ndev);
> > struct sk_buff *new_skb;
> > @@ -1496,6 +1546,78 @@ static bool fec_enet_copybreak(struct net_device
> *ndev, struct sk_buff **skb,
> > return true;
> > }
> >
> > +static void fec_enet_update_cbd(struct fec_enet_priv_rx_q *rxq,
> > + struct bufdesc *bdp, int index) {
> > + struct page *new_page;
> > + dma_addr_t phys_addr;
> > +
> > + new_page = page_pool_dev_alloc_pages(rxq->page_pool);
> > + WARN_ON(!new_page);
> > + rxq->rx_skb_info[index].page = new_page;
> > +
> > + rxq->rx_skb_info[index].offset = FEC_ENET_XDP_HEADROOM;
> > + phys_addr = page_pool_get_dma_addr(new_page) +
> FEC_ENET_XDP_HEADROOM;
> > + bdp->cbd_bufaddr = cpu_to_fec32(phys_addr); }
> > +
> > +static u32
> > +fec_enet_run_xdp(struct fec_enet_private *fep, struct bpf_prog *prog,
> > + struct xdp_buff *xdp, struct fec_enet_priv_rx_q *rxq,
> > +int index) {
> > + unsigned int sync, len = xdp->data_end - xdp->data;
> > + u32 ret = FEC_ENET_XDP_PASS;
> > + struct page *page;
> > + int err;
> > + u32 act;
> > +
> > + act = bpf_prog_run_xdp(prog, xdp);
> > +
> > + /* Due xdp_adjust_tail: DMA sync for_device cover max len CPU touch */
> > + sync = xdp->data_end - xdp->data_hard_start -
> FEC_ENET_XDP_HEADROOM;
> > + sync = max(sync, len);
> > +
> > + switch (act) {
> > + case XDP_PASS:
> > + rxq->stats.xdp_pass++;
> > + ret = FEC_ENET_XDP_PASS;
> > + break;
> > +
> > + case XDP_TX:
> > + rxq->stats.xdp_tx++;
> > + bpf_warn_invalid_xdp_action(fep->netdev, prog, act);
> > + fallthrough;
>
> This fallthrough looks wrong. The next xdp_do_redirect() call will pickup left-
> overs in per CPU bpf_redirect_info.
>

So before the XDP_TX is implemented, this part of codes should reside below the XDP_REDIRECT case?

> > +
> > + case XDP_REDIRECT:
> > + err = xdp_do_redirect(fep->netdev, xdp, prog);
> > + rxq->stats.xdp_redirect++;
> > - dma_unmap_single(&fep->pdev->dev,
...

> > - fec32_to_cpu(bdp->cbd_bufaddr),
> > - FEC_ENET_RX_FRSIZE - fep->rx_align,
> > - DMA_FROM_DEVICE);
> > - }
> > -
> > - prefetch(skb->data - NET_IP_ALIGN);
> > + skb = build_skb(page_address(page), FEC_ENET_RX_FRSIZE);
>
> This looks wrong, I think FEC_ENET_RX_FRSIZE should be replaced by PAGE_SIZE.
> As build_skb() does:
>
> size -= SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
>

Agree. As the current FRSIZE definition did not subtract the sizeof(struct skb_shared_info), I happened to not see the problem during the testing.

Thanks,
Shenwei

> > + skb_reserve(skb, FEC_ENET_XDP_HEADROOM);
>
> The skb_reserve looks correct.
>
> > skb_put(skb, pkt_len - 4);
> > data = skb->data;
> > + page_pool_release_page(rxq->page_pool, page);
>
> Today page_pool have SKB recycle support (you might have looked at drivers
> that didn't utilize this yet), thus you don't need to release the page
> (page_pool_release_page) here. Instead you could simply mark the SKB for
> recycling, unless driver does some page refcnt tricks I didn't notice.
>
> skb_mark_for_recycle(skb);
>
>
> > - if (!is_copybreak && need_swap)
> > + if (need_swap)
> > swap_buffer(data, pkt_len);
> >
> > #if !defined(CONFIG_M5272)
> > @@ -1649,16 +1781,6 @@ fec_enet_rx_queue(struct net_device *ndev, int
> > budget, u16 queue_id)
> …