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Date: Mon, 17 Feb 2020 16:38:00 +0200
From: Ilias Apalodimas <ilias.apalodimas@...aro.org>
To: Denis Kirjanov <kda@...ux-powerpc.org>
Cc: netdev@...r.kernel.org
Subject: Re: [PATCH net-next] xen-netfront: add basic XDP support
Hi Denis,
On Mon, Feb 17, 2020 at 04:04:17PM +0300, Denis Kirjanov wrote:
> the patch adds a basic xdp logic to the netfront driver
>
> Signed-off-by: Denis Kirjanov <kda@...ux-powerpc.org>
> ---
> drivers/net/xen-netfront.c | 125 +++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 125 insertions(+)
>
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index 482c6c8..06dd088 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -44,6 +44,8 @@
> #include <linux/mm.h>
> #include <linux/slab.h>
> #include <net/ip.h>
> +#include <linux/bpf.h>
> +#include <linux/bpf_trace.h>
>
> #include <xen/xen.h>
> #include <xen/xenbus.h>
> @@ -102,6 +104,8 @@ struct netfront_queue {
> char name[QUEUE_NAME_SIZE]; /* DEVNAME-qN */
> struct netfront_info *info;
>
> + struct bpf_prog __rcu *xdp_prog;
> +
> struct napi_struct napi;
>
> /* Split event channels support, tx_* == rx_* when using
> @@ -778,6 +782,53 @@ static int xennet_get_extras(struct netfront_queue *queue,
> return err;
> }
>
> +u32 xennet_run_xdp(struct netfront_queue *queue, struct page *pdata,
> + struct xen_netif_rx_response *rx, struct bpf_prog *prog,
> + struct xdp_buff *xdp)
> +{
> + void *data = page_address(pdata);
> + u32 len = rx->status;
> + struct page *page = NULL;
> + u32 act = XDP_PASS;
> +
> + page = alloc_page(GFP_ATOMIC);
This is not how XDP is supposed to work. You should minimize allocations/free during XDP
processing, since it's one of the reasons XDP is so fast.
The skb->data allocated memory should be allocated either via page_pool API or with any
helper that allocates pages before entering this function.
> + if (!page) {
> + act = XDP_DROP;
> + goto out;
> + }
> +
> + xdp->data_hard_start = page_address(page);
> + xdp->data = xdp->data_hard_start + 256;
Please don't use magic numbers like '256', all those are well defined in the
xdp headers.
> + xdp_set_data_meta_invalid(xdp);
> + xdp->data_end = xdp->data + len;
> + xdp->handle = 0;
> +
> + memcpy(xdp->data, data, len);
Again this should be allocated before, instead of copying it.
> +
> + act = bpf_prog_run_xdp(prog, xdp);
> + switch (act) {
> + case XDP_PASS:
> + case XDP_TX:
> + case XDP_DROP:
> + break;
> +
missing XDP_REDIRECT and .ndo_xdp_xmit,
> + case XDP_ABORTED:
> + trace_xdp_exception(queue->info->netdev, prog, act);
> + break;
> +
> + default:
> + bpf_warn_invalid_xdp_action(act);
> + }
> +
> +out:
> + if (page && act != XDP_PASS && act != XDP_TX) {
> + __free_page(page);
> + xdp->data_hard_start = NULL;
> + }
> +
> + return act;
> +}
> +
> static int xennet_get_responses(struct netfront_queue *queue,
> struct netfront_rx_info *rinfo, RING_IDX rp,
> struct sk_buff_head *list)
> @@ -792,6 +843,9 @@ static int xennet_get_responses(struct netfront_queue *queue,
> int slots = 1;
> int err = 0;
> unsigned long ret;
> + struct bpf_prog *xdp_prog;
> + struct xdp_buff xdp;
> + u32 verdict;
>
> if (rx->flags & XEN_NETRXF_extra_info) {
> err = xennet_get_extras(queue, extras, rp);
> @@ -827,6 +881,21 @@ static int xennet_get_responses(struct netfront_queue *queue,
>
> gnttab_release_grant_reference(&queue->gref_rx_head, ref);
>
> + rcu_read_lock();
> + xdp_prog = rcu_dereference(queue->xdp_prog);
> + if (xdp_prog) {
> + WARN_ON_ONCE(skb_shinfo(skb)->nr_frags != 1);
> + verdict = xennet_run_xdp(queue,
> + skb_frag_page(&skb_shinfo(skb)->frags[0]),
This should run on a single page and not a page fragment. You can check the netsec and mvneta
drivers. They are relatively simple and can give you and idea on how to allocate/recycle pages
properly for XDP.
> + rx, xdp_prog, &xdp);
> +
> + if (verdict != XDP_PASS && verdict != XDP_TX) {
> + err = -EINVAL;
> + goto next;
> + }
> +
> + }
> + rcu_read_unlock();
> __skb_queue_tail(list, skb);
>
> next:
> @@ -1261,6 +1330,61 @@ static void xennet_poll_controller(struct net_device *dev)
> }
> #endif
>
> +static int xennet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
> + struct netlink_ext_ack *extack)
> +{
> + struct netfront_info *np = netdev_priv(dev);
> + struct bpf_prog *old_prog;
> + unsigned int i;
> +
> + old_prog = rtnl_dereference(np->queues[0].xdp_prog);
> + if (!old_prog && !prog)
> + return 0;
> +
> + if (prog)
> + bpf_prog_add(prog, dev->real_num_tx_queues);
> +
> + for (i = 0; i < dev->real_num_tx_queues; ++i)
> + rcu_assign_pointer(np->queues[i].xdp_prog, prog);
> +
> + if (old_prog)
> + for (i = 0; i < dev->real_num_tx_queues; ++i)
> + bpf_prog_put(old_prog);
> +
> + return 0;
> +}
> +
> +static u32 xennet_xdp_query(struct net_device *dev)
> +{
> + struct netfront_info *np = netdev_priv(dev);
> + unsigned int num_queues = dev->real_num_tx_queues;
> + unsigned int i;
> + struct netfront_queue *queue;
> + const struct bpf_prog *xdp_prog;
> +
> + for (i = 0; i < num_queues; ++i) {
> + queue = &np->queues[i];
> + xdp_prog = rtnl_dereference(queue->xdp_prog);
> + if (xdp_prog)
> + return xdp_prog->aux->id;
> + }
> +
> + return 0;
> +}
> +
> +static int xennet_xdp(struct net_device *dev, struct netdev_bpf *xdp)
> +{
> + switch (xdp->command) {
> + case XDP_SETUP_PROG:
> + return xennet_xdp_set(dev, xdp->prog, xdp->extack);
> + case XDP_QUERY_PROG:
> + xdp->prog_id = xennet_xdp_query(dev);
> + return 0;
> + default:
> + return -EINVAL;
> + }
> +}
> +
> static const struct net_device_ops xennet_netdev_ops = {
> .ndo_open = xennet_open,
> .ndo_stop = xennet_close,
> @@ -1272,6 +1396,7 @@ static void xennet_poll_controller(struct net_device *dev)
> .ndo_fix_features = xennet_fix_features,
> .ndo_set_features = xennet_set_features,
> .ndo_select_queue = xennet_select_queue,
> + .ndo_bpf = xennet_xdp,
> #ifdef CONFIG_NET_POLL_CONTROLLER
> .ndo_poll_controller = xennet_poll_controller,
> #endif
> --
> 1.8.3.1
>
Regards
/Ilias
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