[net PATCH 1/2] virtio_net: cap mtu when XDP programs are running

[net PATCH 1/2] virtio_net: cap mtu when XDP programs are running

[John Fastabend]

XDP programs can not consume multiple pages so we cap the MTU to
avoid this case. Virtio-net however only checks the MTU at XDP
program load and does not block MTU changes after the program
has loaded.

This patch sets/clears the max_mtu value at XDP load/unload time.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
---
 drivers/net/virtio_net.c |   26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 4a10500..261103d9 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1699,11 +1699,28 @@ static void virtnet_init_settings(struct net_device *dev)
 	.set_settings = virtnet_set_settings,
 };
 
+#define MIN_MTU ETH_MIN_MTU
+#define MAX_MTU ETH_MAX_MTU
+
+static unsigned long int virtnet_xdp_mtu(struct bpf_prog *prog,
+					 struct virtnet_info *vi)
+{
+	if (!prog && virtio_has_feature(vi->vdev, VIRTIO_NET_F_MTU))
+		return virtio_cread16(vi->vdev,
+				      offsetof(struct virtio_net_config, mtu));
+	else if (!prog)
+		return ETH_MAX_MTU;
+	else if (vi->mergeable_rx_bufs)
+		return PAGE_SIZE - sizeof(struct padded_vnet_hdr);
+	else
+		return GOOD_PACKET_LEN;
+}
+
 static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
 {
-	unsigned long int max_sz = PAGE_SIZE - sizeof(struct padded_vnet_hdr);
 	struct virtnet_info *vi = netdev_priv(dev);
 	struct bpf_prog *old_prog;
+	unsigned long int max_sz;
 	u16 xdp_qp = 0, curr_qp;
 	int i, err;
 
@@ -1720,6 +1737,7 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
 		return -EINVAL;
 	}
 
+	max_sz = virtnet_xdp_mtu(prog, vi);
 	if (dev->mtu > max_sz) {
 		netdev_warn(dev, "XDP requires MTU less than %lu\n", max_sz);
 		return -EINVAL;
@@ -1748,6 +1766,9 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
 			virtnet_set_queues(vi, curr_qp);
 			return PTR_ERR(prog);
 		}
+		dev->max_mtu = max_sz;
+	} else {
+		dev->max_mtu = ETH_MAX_MTU;
 	}
 
 	vi->xdp_queue_pairs = xdp_qp;
@@ -2133,9 +2154,6 @@ static bool virtnet_validate_features(struct virtio_device *vdev)
 	return true;
 }
 
-#define MIN_MTU ETH_MIN_MTU
-#define MAX_MTU ETH_MAX_MTU
-
 static int virtnet_probe(struct virtio_device *vdev)
 {
 	int i, err;

[net PATCH 2/2] virtio_net: use dev_kfree_skb for small buffer XDP receive

[John Fastabend]

In the small buffer case during driver unload we currently use
put_page instead of dev_kfree_skb. Resolve this by adding a check
for virtnet mode when checking XDP queue type. Also name the
function so that the code reads correctly to match the additional
check.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
---
 drivers/net/virtio_net.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 261103d9..a224d3e 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1911,8 +1911,12 @@ static void free_receive_page_frags(struct virtnet_info *vi)
 			put_page(vi->rq[i].alloc_frag.page);
 }
 
-static bool is_xdp_queue(struct virtnet_info *vi, int q)
+static bool is_xdp_raw_buffer_queue(struct virtnet_info *vi, int q)
 {
+	/* For small receive mode always use kfree_skb variants */
+	if (!vi->mergeable_rx_bufs)
+		return false;
+
 	if (q < (vi->curr_queue_pairs - vi->xdp_queue_pairs))
 		return false;
 	else if (q < vi->curr_queue_pairs)
@@ -1929,7 +1933,7 @@ static void free_unused_bufs(struct virtnet_info *vi)
 	for (i = 0; i < vi->max_queue_pairs; i++) {
 		struct virtqueue *vq = vi->sq[i].vq;
 		while ((buf = virtqueue_detach_unused_buf(vq)) != NULL) {
-			if (!is_xdp_queue(vi, i))
+			if (!is_xdp_raw_buffer_queue(vi, i))
 				dev_kfree_skb(buf);
 			else
 				put_page(virt_to_head_page(buf));

Re: [net PATCH 1/2] virtio_net: cap mtu when XDP programs are running

[John Fastabend]

On 17-01-04 07:11 PM, John Fastabend wrote:
> XDP programs can not consume multiple pages so we cap the MTU to
> avoid this case. Virtio-net however only checks the MTU at XDP
> program load and does not block MTU changes after the program
> has loaded.
> 
> This patch sets/clears the max_mtu value at XDP load/unload time.
> 
> Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
> ---
>  drivers/net/virtio_net.c |   26 ++++++++++++++++++++++----
>  1 file changed, 22 insertions(+), 4 deletions(-)


[...]

>  static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
>  {
> -	unsigned long int max_sz = PAGE_SIZE - sizeof(struct padded_vnet_hdr);
>  	struct virtnet_info *vi = netdev_priv(dev);
>  	struct bpf_prog *old_prog;
> +	unsigned long int max_sz;
>  	u16 xdp_qp = 0, curr_qp;
>  	int i, err;
>  
> @@ -1720,6 +1737,7 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
>  		return -EINVAL;
>  	}
>  
> +	max_sz = virtnet_xdp_mtu(prog, vi);
>  	if (dev->mtu > max_sz) {
>  		netdev_warn(dev, "XDP requires MTU less than %lu\n", max_sz);
>  		return -EINVAL;
> @@ -1748,6 +1766,9 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
>  			virtnet_set_queues(vi, curr_qp);
>  			return PTR_ERR(prog);
>  		}
> +		dev->max_mtu = max_sz;
> +	} else {
> +		dev->max_mtu = ETH_MAX_MTU;
>  	}

oops v2 needed. The else branch is not required anymore. :/

Re: [net PATCH 1/2] virtio_net: cap mtu when XDP programs are running

[Michael S. Tsirkin]

On Wed, Jan 04, 2017 at 07:11:18PM -0800, John Fastabend wrote:
> XDP programs can not consume multiple pages so we cap the MTU to
> avoid this case. Virtio-net however only checks the MTU at XDP
> program load and does not block MTU changes after the program
> has loaded.

Do drivers really have to tweak max mtu all the time?
Seems strange, I would say drivers just report device caps
and net core enforces rules.
Can't net core do these checks?

> 
> This patch sets/clears the max_mtu value at XDP load/unload time.
> 
> Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
> ---
>  drivers/net/virtio_net.c |   26 ++++++++++++++++++++++----
>  1 file changed, 22 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 4a10500..261103d9 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1699,11 +1699,28 @@ static void virtnet_init_settings(struct net_device *dev)
>  	.set_settings = virtnet_set_settings,
>  };
>  
> +#define MIN_MTU ETH_MIN_MTU
> +#define MAX_MTU ETH_MAX_MTU
> +
> +static unsigned long int virtnet_xdp_mtu(struct bpf_prog *prog,
> +					 struct virtnet_info *vi)
> +{
> +	if (!prog && virtio_has_feature(vi->vdev, VIRTIO_NET_F_MTU))
> +		return virtio_cread16(vi->vdev,
> +				      offsetof(struct virtio_net_config, mtu));
> +	else if (!prog)
> +		return ETH_MAX_MTU;
> +	else if (vi->mergeable_rx_bufs)
> +		return PAGE_SIZE - sizeof(struct padded_vnet_hdr);
> +	else
> +		return GOOD_PACKET_LEN;
> +}
> +
>  static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
>  {
> -	unsigned long int max_sz = PAGE_SIZE - sizeof(struct padded_vnet_hdr);
>  	struct virtnet_info *vi = netdev_priv(dev);
>  	struct bpf_prog *old_prog;
> +	unsigned long int max_sz;
>  	u16 xdp_qp = 0, curr_qp;
>  	int i, err;
>  
> @@ -1720,6 +1737,7 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
>  		return -EINVAL;
>  	}
>  
> +	max_sz = virtnet_xdp_mtu(prog, vi);
>  	if (dev->mtu > max_sz) {
>  		netdev_warn(dev, "XDP requires MTU less than %lu\n", max_sz);
>  		return -EINVAL;
> @@ -1748,6 +1766,9 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
>  			virtnet_set_queues(vi, curr_qp);
>  			return PTR_ERR(prog);
>  		}
> +		dev->max_mtu = max_sz;
> +	} else {
> +		dev->max_mtu = ETH_MAX_MTU;
>  	}
>  
>  	vi->xdp_queue_pairs = xdp_qp;
> @@ -2133,9 +2154,6 @@ static bool virtnet_validate_features(struct virtio_device *vdev)
>  	return true;
>  }
>  
> -#define MIN_MTU ETH_MIN_MTU
> -#define MAX_MTU ETH_MAX_MTU
> -
>  static int virtnet_probe(struct virtio_device *vdev)
>  {
>  	int i, err;

Re: [net PATCH 1/2] virtio_net: cap mtu when XDP programs are running

[Jason Wang]

On 2017年01月05日 11:18, Michael S. Tsirkin wrote:
> On Wed, Jan 04, 2017 at 07:11:18PM -0800, John Fastabend wrote:
>> XDP programs can not consume multiple pages so we cap the MTU to
>> avoid this case. Virtio-net however only checks the MTU at XDP
>> program load and does not block MTU changes after the program
>> has loaded.
> Do drivers really have to tweak max mtu all the time?
> Seems strange, I would say drivers just report device caps
> and net core enforces rules.
> Can't net core do these checks?

I think this needs host co-operation, at least this patch prevents user 
from misconfiguring mtu in guest.