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Date: Thu, 01 Apr 2021 13:26:02 +0200
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Vladimir Oltean <olteanv@...il.com>,
Jakub Kicinski <kuba@...nel.org>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Jesper Dangaard Brouer <hawk@...nel.org>,
John Fastabend <john.fastabend@...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>,
"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
bpf@...r.kernel.org
Cc: Alexander Duyck <alexander.duyck@...il.com>,
Ioana Ciornei <ioana.ciornei@....com>,
Alex Marginean <alexandru.marginean@....com>,
Claudiu Manoil <claudiu.manoil@....com>,
Ilias Apalodimas <ilias.apalodimas@...aro.org>,
Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [PATCH net-next 9/9] net: enetc: add support for XDP_REDIRECT
Vladimir Oltean <olteanv@...il.com> writes:
> From: Vladimir Oltean <vladimir.oltean@....com>
>
> The driver implementation of the XDP_REDIRECT action reuses parts from
> XDP_TX, most notably the enetc_xdp_tx function which transmits an array
> of TX software BDs. Only this time, the buffers don't have DMA mappings,
> we need to create them.
>
> When a BPF program reaches the XDP_REDIRECT verdict for a frame, we can
> employ the same buffer reuse strategy as for the normal processing path
> and for XDP_PASS: we can flip to the other page half and seed that to
> the RX ring.
>
> Note that scatter/gather support is there, but disabled due to lack of
> multi-buffer support in XDP (which is added by this series):
> https://patchwork.kernel.org/project/netdevbpf/cover/cover.1616179034.git.lorenzo@kernel.org/
>
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> ---
> drivers/net/ethernet/freescale/enetc/enetc.c | 212 +++++++++++++++++-
> drivers/net/ethernet/freescale/enetc/enetc.h | 11 +-
> .../ethernet/freescale/enetc/enetc_ethtool.c | 6 +
> .../net/ethernet/freescale/enetc/enetc_pf.c | 1 +
> 4 files changed, 218 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c b/drivers/net/ethernet/freescale/enetc/enetc.c
> index ba5313a5d7a4..57049ae97201 100644
> --- a/drivers/net/ethernet/freescale/enetc/enetc.c
> +++ b/drivers/net/ethernet/freescale/enetc/enetc.c
> @@ -8,6 +8,23 @@
> #include <linux/vmalloc.h>
> #include <net/pkt_sched.h>
>
> +static struct sk_buff *enetc_tx_swbd_get_skb(struct enetc_tx_swbd *tx_swbd)
> +{
> + if (tx_swbd->is_xdp_tx || tx_swbd->is_xdp_redirect)
> + return NULL;
> +
> + return tx_swbd->skb;
> +}
> +
> +static struct xdp_frame *
> +enetc_tx_swbd_get_xdp_frame(struct enetc_tx_swbd *tx_swbd)
> +{
> + if (tx_swbd->is_xdp_redirect)
> + return tx_swbd->xdp_frame;
> +
> + return NULL;
> +}
> +
> static void enetc_unmap_tx_buff(struct enetc_bdr *tx_ring,
> struct enetc_tx_swbd *tx_swbd)
> {
> @@ -25,14 +42,20 @@ static void enetc_unmap_tx_buff(struct enetc_bdr *tx_ring,
> tx_swbd->dma = 0;
> }
>
> -static void enetc_free_tx_skb(struct enetc_bdr *tx_ring,
> - struct enetc_tx_swbd *tx_swbd)
> +static void enetc_free_tx_frame(struct enetc_bdr *tx_ring,
> + struct enetc_tx_swbd *tx_swbd)
> {
> + struct xdp_frame *xdp_frame = enetc_tx_swbd_get_xdp_frame(tx_swbd);
> + struct sk_buff *skb = enetc_tx_swbd_get_skb(tx_swbd);
> +
> if (tx_swbd->dma)
> enetc_unmap_tx_buff(tx_ring, tx_swbd);
>
> - if (tx_swbd->skb) {
> - dev_kfree_skb_any(tx_swbd->skb);
> + if (xdp_frame) {
> + xdp_return_frame(tx_swbd->xdp_frame);
> + tx_swbd->xdp_frame = NULL;
> + } else if (skb) {
> + dev_kfree_skb_any(skb);
> tx_swbd->skb = NULL;
> }
> }
> @@ -183,7 +206,7 @@ static int enetc_map_tx_buffs(struct enetc_bdr *tx_ring, struct sk_buff *skb,
>
> do {
> tx_swbd = &tx_ring->tx_swbd[i];
> - enetc_free_tx_skb(tx_ring, tx_swbd);
> + enetc_free_tx_frame(tx_ring, tx_swbd);
> if (i == 0)
> i = tx_ring->bd_count;
> i--;
> @@ -381,6 +404,9 @@ static bool enetc_clean_tx_ring(struct enetc_bdr *tx_ring, int napi_budget)
> do_tstamp = false;
>
> while (bds_to_clean && tx_frm_cnt < ENETC_DEFAULT_TX_WORK) {
> + struct xdp_frame *xdp_frame = enetc_tx_swbd_get_xdp_frame(tx_swbd);
> + struct sk_buff *skb = enetc_tx_swbd_get_skb(tx_swbd);
> +
> if (unlikely(tx_swbd->check_wb)) {
> struct enetc_ndev_priv *priv = netdev_priv(ndev);
> union enetc_tx_bd *txbd;
> @@ -400,12 +426,15 @@ static bool enetc_clean_tx_ring(struct enetc_bdr *tx_ring, int napi_budget)
> else if (likely(tx_swbd->dma))
> enetc_unmap_tx_buff(tx_ring, tx_swbd);
>
> - if (tx_swbd->skb) {
> + if (xdp_frame) {
> + xdp_return_frame(xdp_frame);
> + tx_swbd->xdp_frame = NULL;
> + } else if (skb) {
> if (unlikely(do_tstamp)) {
> - enetc_tstamp_tx(tx_swbd->skb, tstamp);
> + enetc_tstamp_tx(skb, tstamp);
> do_tstamp = false;
> }
> - napi_consume_skb(tx_swbd->skb, napi_budget);
> + napi_consume_skb(skb, napi_budget);
> tx_swbd->skb = NULL;
> }
>
> @@ -827,6 +856,109 @@ static bool enetc_xdp_tx(struct enetc_bdr *tx_ring,
> return true;
> }
>
> +static int enetc_xdp_frame_to_xdp_tx_swbd(struct enetc_bdr *tx_ring,
> + struct enetc_tx_swbd *xdp_tx_arr,
> + struct xdp_frame *xdp_frame)
> +{
> + struct enetc_tx_swbd *xdp_tx_swbd = &xdp_tx_arr[0];
> + struct skb_shared_info *shinfo;
> + void *data = xdp_frame->data;
> + int len = xdp_frame->len;
> + skb_frag_t *frag;
> + dma_addr_t dma;
> + unsigned int f;
> + int n = 0;
> +
> + dma = dma_map_single(tx_ring->dev, data, len, DMA_TO_DEVICE);
> + if (unlikely(dma_mapping_error(tx_ring->dev, dma))) {
> + netdev_err(tx_ring->ndev, "DMA map error\n");
> + return -1;
> + }
> +
> + xdp_tx_swbd->dma = dma;
> + xdp_tx_swbd->dir = DMA_TO_DEVICE;
> + xdp_tx_swbd->len = len;
> + xdp_tx_swbd->is_xdp_redirect = true;
> + xdp_tx_swbd->is_eof = false;
> + xdp_tx_swbd->xdp_frame = NULL;
> +
> + n++;
> + xdp_tx_swbd = &xdp_tx_arr[n];
> +
> + shinfo = xdp_get_shared_info_from_frame(xdp_frame);
> +
> + for (f = 0, frag = &shinfo->frags[0]; f < shinfo->nr_frags;
> + f++, frag++) {
> + data = skb_frag_address(frag);
> + len = skb_frag_size(frag);
> +
> + dma = dma_map_single(tx_ring->dev, data, len, DMA_TO_DEVICE);
> + if (unlikely(dma_mapping_error(tx_ring->dev, dma))) {
> + /* Undo the DMA mapping for all fragments */
> + while (n-- >= 0)
> + enetc_unmap_tx_buff(tx_ring, &xdp_tx_arr[n]);
> +
> + netdev_err(tx_ring->ndev, "DMA map error\n");
> + return -1;
> + }
> +
> + xdp_tx_swbd->dma = dma;
> + xdp_tx_swbd->dir = DMA_TO_DEVICE;
> + xdp_tx_swbd->len = len;
> + xdp_tx_swbd->is_xdp_redirect = true;
> + xdp_tx_swbd->is_eof = false;
> + xdp_tx_swbd->xdp_frame = NULL;
> +
> + n++;
> + xdp_tx_swbd = &xdp_tx_arr[n];
> + }
> +
> + xdp_tx_arr[n - 1].is_eof = true;
> + xdp_tx_arr[n - 1].xdp_frame = xdp_frame;
> +
> + return n;
> +}
> +
> +int enetc_xdp_xmit(struct net_device *ndev, int num_frames,
> + struct xdp_frame **frames, u32 flags)
> +{
> + struct enetc_tx_swbd xdp_redirect_arr[ENETC_MAX_SKB_FRAGS] = {0};
> + struct enetc_ndev_priv *priv = netdev_priv(ndev);
> + struct enetc_bdr *tx_ring;
> + int xdp_tx_bd_cnt, i, k;
> + int xdp_tx_frm_cnt = 0;
> +
> + tx_ring = priv->tx_ring[smp_processor_id()];
What mechanism guarantees that this won't overflow the array? :)
-Toke
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