[PATCH net-next] xen-netfront: add basic XDP support

[PATCH net-next] xen-netfront: add basic XDP support

[Denis Kirjanov]

the patch adds a basic xdp logic to the netfront driver

Signed-off-by: Denis Kirjanov <kda@linux-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);
+	if (!page) {
+		act = XDP_DROP;
+		goto out;
+	}
+
+	xdp->data_hard_start = page_address(page);
+	xdp->data = xdp->data_hard_start + 256;
+	xdp_set_data_meta_invalid(xdp);
+	xdp->data_end = xdp->data + len;
+	xdp->handle = 0;
+
+	memcpy(xdp->data, data, len);
+
+	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);
+	}
+
+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]),
+				       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

Re: [PATCH net-next] xen-netfront: add basic XDP support

[Ilias Apalodimas]

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@linux-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