Date:   Wed, 4 Mar 2020 16:10:58 +0300
From:   Denis Kirjanov <kda@...ux-powerpc.org>
To:     Jürgen Groß <jgross@...e.com>
Cc:     netdev@...r.kernel.org,
        "ilias.apalodimas" <ilias.apalodimas@...aro.org>,
        wei.liu@...nel.org, paul@....org
Subject: Re: [PATCH net-next v2] xen-netfront: add basic XDP support

On 3/2/20, Jürgen Groß <jgross@...e.com> wrote:
> 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?
Here we just ask xen-backend to make a headroom, that's it.
It's better to send xen-backend changes in a separate patch.

>
> 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.

I don't think that it's going to switch often and more likely it's a one shot
action.

>
>
> Juergen
>

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