netdev - Re: [PATCH net 7/7] virtio_net: Differentiate sk_buff and xdp

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Message-ID: <669e0ca6-c095-75eb-66ec-b9f3ab5e58de@redhat.com>
Date:   Thu, 17 Jan 2019 21:04:30 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Toshiaki Makita <makita.toshiaki@....ntt.co.jp>,
        "David S. Miller" <davem@...emloft.net>,
        "Michael S. Tsirkin" <mst@...hat.com>
Cc:     netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH net 7/7] virtio_net: Differentiate sk_buff and xdp_frame
 on freeing


On 2019/1/17 7:20, Toshiaki Makita wrote:
> We do not reset or free up unused buffers when enabling/disabling XDP,
> so it can happen that xdp_frames are freed after disabling XDP or
> sk_buffs are freed after enabling XDP on xdp tx queues.
> Thus we need to handle both forms (xdp_frames and sk_buffs) regardless
> of XDP setting.
> One way to trigger this problem is to disable XDP when napi_tx is
> enabled. In that case, virtnet_xdp_set() calls virtnet_napi_enable()
> which kicks NAPI. The NAPI handler will call virtnet_poll_cleantx()
> which invokes free_old_xmit_skbs() for queues which have been used by
> XDP.
>
> Note that even with this change we need to keep skipping
> free_old_xmit_skbs() from NAPI handlers when XDP is enabled, because XDP
> tx queues do not aquire queue locks.
>
> Fixes: 4941d472bf95 ("virtio-net: do not reset during XDP set")
> Signed-off-by: Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
> ---
>   drivers/net/virtio_net.c | 54 +++++++++++++++++++++++++++++++++++++-----------
>   1 file changed, 42 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 996de69..6598c25 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -57,6 +57,8 @@
>   #define VIRTIO_XDP_TX		BIT(0)
>   #define VIRTIO_XDP_REDIR	BIT(1)
>   
> +#define VIRTIO_XDP_FLAG	BIT(0)
> +
>   /* RX packet size EWMA. The average packet size is used to determine the packet
>    * buffer size when refilling RX rings. As the entire RX ring may be refilled
>    * at once, the weight is chosen so that the EWMA will be insensitive to short-
> @@ -252,6 +254,21 @@ struct padded_vnet_hdr {
>   	char padding[4];
>   };
>   
> +static bool is_xdp_frame(void *ptr)
> +{
> +	return (unsigned long)ptr & VIRTIO_XDP_FLAG;
> +}
> +
> +static void *xdp_to_ptr(struct xdp_frame *ptr)
> +{
> +	return (void *)((unsigned long)ptr | VIRTIO_XDP_FLAG);
> +}
> +
> +static struct xdp_frame *ptr_to_xdp(void *ptr)
> +{
> +	return (struct xdp_frame *)((unsigned long)ptr & ~VIRTIO_XDP_FLAG);
> +}
> +
>   /* Converting between virtqueue no. and kernel tx/rx queue no.
>    * 0:rx0 1:tx0 2:rx1 3:tx1 ... 2N:rxN 2N+1:txN 2N+2:cvq
>    */
> @@ -462,7 +479,8 @@ static int __virtnet_xdp_xmit_one(struct virtnet_info *vi,
>   
>   	sg_init_one(sq->sg, xdpf->data, xdpf->len);
>   
> -	err = virtqueue_add_outbuf(sq->vq, sq->sg, 1, xdpf, GFP_ATOMIC);
> +	err = virtqueue_add_outbuf(sq->vq, sq->sg, 1, xdp_to_ptr(xdpf),
> +				   GFP_ATOMIC);
>   	if (unlikely(err))
>   		return -ENOSPC; /* Caller handle free/refcnt */
>   
> @@ -482,13 +500,13 @@ static int virtnet_xdp_xmit(struct net_device *dev,
>   {
>   	struct virtnet_info *vi = netdev_priv(dev);
>   	struct receive_queue *rq = vi->rq;
> -	struct xdp_frame *xdpf_sent;
>   	struct bpf_prog *xdp_prog;
>   	struct send_queue *sq;
>   	unsigned int len;
>   	int drops = 0;
>   	int kicks = 0;
>   	int ret, err;
> +	void *ptr;
>   	int i;
>   
>   	/* Only allow ndo_xdp_xmit if XDP is loaded on dev, as this
> @@ -507,8 +525,12 @@ static int virtnet_xdp_xmit(struct net_device *dev,
>   	}
>   
>   	/* Free up any pending old buffers before queueing new ones. */
> -	while ((xdpf_sent = virtqueue_get_buf(sq->vq, &len)) != NULL)
> -		xdp_return_frame(xdpf_sent);
> +	while ((ptr = virtqueue_get_buf(sq->vq, &len)) != NULL) {
> +		if (likely(is_xdp_frame(ptr)))
> +			xdp_return_frame(ptr_to_xdp(ptr));
> +		else
> +			dev_consume_skb_any(ptr);
> +	}
>   
>   	for (i = 0; i < n; i++) {
>   		struct xdp_frame *xdpf = frames[i];
> @@ -1329,18 +1351,26 @@ static int virtnet_receive(struct receive_queue *rq, int budget,
>   
>   static void free_old_xmit_skbs(struct send_queue *sq)
>   {
> -	struct sk_buff *skb;
>   	unsigned int len;
>   	unsigned int packets = 0;
>   	unsigned int bytes = 0;
> +	void *ptr;
>   
> -	while ((skb = virtqueue_get_buf(sq->vq, &len)) != NULL) {
> -		pr_debug("Sent skb %p\n", skb);
> +	while ((ptr = virtqueue_get_buf(sq->vq, &len)) != NULL) {
> +		if (likely(!is_xdp_frame(ptr))) {
> +			struct sk_buff *skb = ptr;
>   
> -		bytes += skb->len;
> -		packets++;
> +			pr_debug("Sent skb %p\n", skb);
>   
> -		dev_consume_skb_any(skb);
> +			bytes += skb->len;
> +			dev_consume_skb_any(skb);
> +		} else {
> +			struct xdp_frame *frame = ptr_to_xdp(ptr);
> +
> +			bytes += frame->len;
> +			xdp_return_frame(frame);
> +		}
> +		packets++;
>   	}
>   
>   	/* Avoid overhead when no packets have been processed
> @@ -2665,10 +2695,10 @@ 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_raw_buffer_queue(vi, i))
> +			if (!is_xdp_frame(buf))
>   				dev_kfree_skb(buf);
>   			else
> -				xdp_return_frame(buf);
> +				xdp_return_frame(ptr_to_xdp(buf));
>   		}
>   	}
>   


Acked-by: Jason Wang <jasowang@...hat.com>

Thanks!