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Date: Mon, 2 Mar 2020 16:29:41 +0100
From: Jürgen Groß <jgross@...e.com>
To: Denis Kirjanov <kda@...ux-powerpc.org>, netdev@...r.kernel.org
Cc: ilias.apalodimas@...aro.org
Subject: Re: [PATCH net-next v2] xen-netfront: add basic XDP support
On 02.03.20 15:21, Denis Kirjanov wrote:
> the patch adds a basic xdo logic to the netfront driver
>
> XDP redirect is not supported yet
>
> v2:
> - avoid data copying while passing to XDP
> - tell xen-natback that we need the headroom space
Please add the patch history below the "---" delimiter
>
> Signed-off-by: Denis Kirjanov <kda@...ux-powerpc.org>
> ---
> drivers/net/xen-netback/common.h | 1 +
> drivers/net/xen-netback/rx.c | 9 ++-
> drivers/net/xen-netback/xenbus.c | 21 ++++++
> drivers/net/xen-netfront.c | 157 +++++++++++++++++++++++++++++++++++++++
> 4 files changed, 186 insertions(+), 2 deletions(-)
You are modifying xen-netback sources. Please Cc the maintainers.
>
> diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-netback/common.h
> index 05847eb..0750c6f 100644
> --- a/drivers/net/xen-netback/common.h
> +++ b/drivers/net/xen-netback/common.h
> @@ -280,6 +280,7 @@ struct xenvif {
> u8 ip_csum:1;
> u8 ipv6_csum:1;
> u8 multicast_control:1;
> + u8 xdp_enabled:1;
>
> /* Is this interface disabled? True when backend discovers
> * frontend is rogue.
> diff --git a/drivers/net/xen-netback/rx.c b/drivers/net/xen-netback/rx.c
> index ef58870..a110a59 100644
> --- a/drivers/net/xen-netback/rx.c
> +++ b/drivers/net/xen-netback/rx.c
> @@ -33,6 +33,11 @@
> #include <xen/xen.h>
> #include <xen/events.h>
>
> +static inline int xenvif_rx_xdp_offset(struct xenvif *vif)
> +{
> + return (vif->xdp_enabled ? XDP_PACKET_HEADROOM : 0);
> +}
> +
> static bool xenvif_rx_ring_slots_available(struct xenvif_queue *queue)
> {
> RING_IDX prod, cons;
> @@ -356,7 +361,7 @@ static void xenvif_rx_data_slot(struct xenvif_queue *queue,
> struct xen_netif_rx_request *req,
> struct xen_netif_rx_response *rsp)
> {
> - unsigned int offset = 0;
> + unsigned int offset = xenvif_rx_xdp_offset(queue->vif);
> unsigned int flags;
>
> do {
> @@ -389,7 +394,7 @@ static void xenvif_rx_data_slot(struct xenvif_queue *queue,
> flags |= XEN_NETRXF_extra_info;
> }
>
> - rsp->offset = 0;
> + rsp->offset = xenvif_rx_xdp_offset(queue->vif);
> rsp->flags = flags;
> rsp->id = req->id;
> rsp->status = (s16)offset;
> diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-netback/xenbus.c
> index 286054b..81a6023 100644
> --- a/drivers/net/xen-netback/xenbus.c
> +++ b/drivers/net/xen-netback/xenbus.c
> @@ -393,6 +393,20 @@ static void set_backend_state(struct backend_info *be,
> }
> }
>
> +static void read_xenbus_fronetend_xdp(struct backend_info *be,
> + struct xenbus_device *dev)
Typo: s/fronetend/frontend/
> +{
> + struct xenvif *vif = be->vif;
> + unsigned int val;
> + int err;
> +
> + err = xenbus_scanf(XBT_NIL, dev->otherend,
> + "feature-xdp", "%u", &val);
> + if (err < 0)
> + return;
> + vif->xdp_enabled = val;
> +}
> +
> /**
> * Callback received when the frontend's state changes.
> */
> @@ -417,6 +431,11 @@ static void frontend_changed(struct xenbus_device *dev,
> set_backend_state(be, XenbusStateConnected);
> break;
>
> + case XenbusStateReconfiguring:
> + read_xenbus_fronetend_xdp(be, dev);
> + xenbus_switch_state(dev, XenbusStateReconfigured);
> + break;
> +
Where is the reaction to the backend being set to "Reconfigured"?
> case XenbusStateClosing:
> set_backend_state(be, XenbusStateClosing);
> break;
> @@ -935,6 +954,8 @@ static int read_xenbus_vif_flags(struct backend_info *be)
>
> vif->gso_mask = 0;
>
> + vif->xdp_enabled = 0;
> +
> if (xenbus_read_unsigned(dev->otherend, "feature-gso-tcpv4", 0))
> vif->gso_mask |= GSO_BIT(TCPV4);
>
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index 482c6c8..db8a280 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 +782,40 @@ 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)
> +{
> + u32 len = rx->status;
> + u32 act = XDP_PASS;
> +
> + xdp->data_hard_start = page_address(pdata);
> + xdp->data = xdp->data_hard_start + XDP_PACKET_HEADROOM;
> + xdp_set_data_meta_invalid(xdp);
> + xdp->data_end = xdp->data + len;
> + xdp->handle = 0;
> +
> + act = bpf_prog_run_xdp(prog, xdp);
> + switch (act) {
> + case XDP_PASS:
> + case XDP_TX:
> + case XDP_DROP:
> + break;
> +
> + case XDP_ABORTED:
> + trace_xdp_exception(queue->info->netdev, prog, act);
> + break;
> +
> + default:
> + bpf_warn_invalid_xdp_action(act);
> + }
> +
> + if (act != XDP_PASS && act != XDP_TX)
> + 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 +830,9 @@ 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 +868,22 @@ 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) {
> + /* currently only a single page contains data */
> + WARN_ON_ONCE(skb_shinfo(skb)->nr_frags != 1);
> + verdict = xennet_run_xdp(queue,
> + skb_frag_page(&skb_shinfo(skb)->frags[0]),
> + 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 +1318,105 @@ static void xennet_poll_controller(struct net_device *dev)
> }
> #endif
>
> +#define NETBACK_XDP_HEADROOM_DISABLE 0
> +#define NETBACK_XDP_HEADROOM_ENABLE 1
> +
> +static int talk_to_netback_xdp(struct netfront_info *np, int xdp)
> +{
> + struct xenbus_transaction xbt;
> + const char *message;
> + int err;
> +
> +again:
> + err = xenbus_transaction_start(&xbt);
> + if (err) {
> + xenbus_dev_fatal(np->xbdev, err, "starting transaction");
> + goto out;
> + }
> +
> + err = xenbus_printf(xbt, np->xbdev->nodename, "feature-xdp", "%d", xdp);
> + if (err) {
> + message = "writing feature-xdp";
> + goto abort_transaction;
> + }
> +
> + err = xenbus_transaction_end(xbt, 0);
> + if (err) {
> + if (err == -EAGAIN)
> + goto again;
Writing a single node to Xenstore doesn't need a transaction.
> + }
> +
> + return 0;
> +
> +abort_transaction:
> + xenbus_dev_fatal(np->xbdev, err, "%s", message);
> + xenbus_transaction_end(xbt, 1);
> +out:
> + return err;
> +}
> +
> +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, err;
> +
> + 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);
> +
> + err = talk_to_netback_xdp(np, old_prog ? NETBACK_XDP_HEADROOM_DISABLE:
> + NETBACK_XDP_HEADROOM_ENABLE);
> + if (err)
> + return err;
> +
> + xenbus_switch_state(np->xbdev, XenbusStateReconfiguring);
What is happening in case the backend doesn't support XDP?
Is it really a good idea to communicate xdp_set via a frontend state
change? This will be rather slow. OTOH I have no idea how often this
might happen.
Juergen
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