Subject: Re: [PATCH net] virtio_net: split out ctrl buffer

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 19 Apr 2018 08:18:55 +0300

On Thu, Apr 19, 2018 at 08:01:49AM +0300, Michael S. Tsirkin wrote:
> When sending control commands, virtio net sets up several buffers for
> DMA. The buffers are all part of the net device which means it's
> actually allocated by kvmalloc so in theory (on extreme memory pressure)
> it's possible to get a vmalloc'ed buffer which on some platforms means
> we can't DMA there.
> 
> Fix up by moving the DMA buffers out into a separate structure.
> 
> Reported-by: Mikulas Patocka <[email-masked]>
> Suggested-by: Eric Dumazet <[email-masked]>
> Signed-off-by: Michael S. Tsirkin <[email-masked]>

Ouch forgot to commit a fix. Pls ignore will send v2 now.

> ---
> 
> Lightly tested.
> Mikulas, does this address your problem?
> 
>  drivers/net/virtio_net.c | 68 +++++++++++++++++++++++++++---------------------
>  1 file changed, 39 insertions(+), 29 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 7b187ec..82f50e5 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -147,6 +147,17 @@ struct receive_queue {
>  	struct xdp_rxq_info xdp_rxq;
>  };
>  
> +/* Control VQ buffers: protected by the rtnl lock */
> +struct control_buf {
> +	struct virtio_net_ctrl_hdr hdr;
> +	virtio_net_ctrl_ack status;
> +	struct virtio_net_ctrl_mq mq;
> +	u8 promisc;
> +	u8 allmulti;
> +	u16 vid;
> +	u64 offloads;
> +};
> +
>  struct virtnet_info {
>  	struct virtio_device *vdev;
>  	struct virtqueue *cvq;
> @@ -192,14 +203,7 @@ struct virtnet_info {
>  	struct hlist_node node;
>  	struct hlist_node node_dead;
>  
> -	/* Control VQ buffers: protected by the rtnl lock */
> -	struct virtio_net_ctrl_hdr ctrl_hdr;
> -	virtio_net_ctrl_ack ctrl_status;
> -	struct virtio_net_ctrl_mq ctrl_mq;
> -	u8 ctrl_promisc;
> -	u8 ctrl_allmulti;
> -	u16 ctrl_vid;
> -	u64 ctrl_offloads;
> +	struct control_buf *ctrl;
>  
>  	/* Ethtool settings */
>  	u8 duplex;
> @@ -1454,25 +1458,25 @@ static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
>  	/* Caller should know better */
>  	BUG_ON(!virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_VQ));
>  
> -	vi->ctrl_status = ~0;
> -	vi->ctrl_hdr.class = class;
> -	vi->ctrl_hdr.cmd = cmd;
> +	vi->ctrl->status = ~0;
> +	vi->ctrl->hdr.class = class;
> +	vi->ctrl->hdr.cmd = cmd;
>  	/* Add header */
> -	sg_init_one(&hdr, &vi->ctrl_hdr, sizeof(vi->ctrl_hdr));
> +	sg_init_one(&hdr, &vi->ctrl->hdr, sizeof(vi->ctrl->hdr));
>  	sgs[out_num++] = &hdr;
>  
>  	if (out)
>  		sgs[out_num++] = out;
>  
>  	/* Add return status. */
> -	sg_init_one(&stat, &vi->ctrl_status, sizeof(vi->ctrl_status));
> +	sg_init_one(&stat, &vi->ctrl->status, sizeof(vi->ctrl->status));
>  	sgs[out_num] = &stat;
>  
>  	BUG_ON(out_num + 1 > ARRAY_SIZE(sgs));
>  	virtqueue_add_sgs(vi->cvq, sgs, out_num, 1, vi, GFP_ATOMIC);
>  
>  	if (unlikely(!virtqueue_kick(vi->cvq)))
> -		return vi->ctrl_status == VIRTIO_NET_OK;
> +		return vi->ctrl->status == VIRTIO_NET_OK;
>  
>  	/* Spin for a response, the kick causes an ioport write, trapping
>  	 * into the hypervisor, so the request should be handled immediately.
> @@ -1481,7 +1485,7 @@ static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
>  	       !virtqueue_is_broken(vi->cvq))
>  		cpu_relax();
>  
> -	return vi->ctrl_status == VIRTIO_NET_OK;
> +	return vi->ctrl->status == VIRTIO_NET_OK;
>  }
>  
>  static int virtnet_set_mac_address(struct net_device *dev, void *p)
> @@ -1593,8 +1597,8 @@ static int _virtnet_set_queues(struct virtnet_info *vi, u16 queue_pairs)
>  	if (!vi->has_cvq || !virtio_has_feature(vi->vdev, VIRTIO_NET_F_MQ))
>  		return 0;
>  
> -	vi->ctrl_mq.virtqueue_pairs = cpu_to_virtio16(vi->vdev, queue_pairs);
> -	sg_init_one(&sg, &vi->ctrl_mq, sizeof(vi->ctrl_mq));
> +	vi->ctrl->mq.virtqueue_pairs = cpu_to_virtio16(vi->vdev, queue_pairs);
> +	sg_init_one(&sg, &vi->ctrl->mq, sizeof(vi->ctrl->mq));
>  
>  	if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_MQ,
>  				  VIRTIO_NET_CTRL_MQ_VQ_PAIRS_SET, &sg)) {
> @@ -1653,22 +1657,22 @@ static void virtnet_set_rx_mode(struct net_device *dev)
>  	if (!virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_RX))
>  		return;
>  
> -	vi->ctrl_promisc = ((dev->flags & IFF_PROMISC) != 0);
> -	vi->ctrl_allmulti = ((dev->flags & IFF_ALLMULTI) != 0);
> +	vi->ctrl->promisc = ((dev->flags & IFF_PROMISC) != 0);
> +	vi->ctrl->allmulti = ((dev->flags & IFF_ALLMULTI) != 0);
>  
> -	sg_init_one(sg, &vi->ctrl_promisc, sizeof(vi->ctrl_promisc));
> +	sg_init_one(sg, &vi->ctrl->promisc, sizeof(vi->ctrl->promisc));
>  
>  	if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_RX,
>  				  VIRTIO_NET_CTRL_RX_PROMISC, sg))
>  		dev_warn(&dev->dev, "Failed to %sable promisc mode.\n",
> -			 vi->ctrl_promisc ? "en" : "dis");
> +			 vi->ctrl->promisc ? "en" : "dis");
>  
> -	sg_init_one(sg, &vi->ctrl_allmulti, sizeof(vi->ctrl_allmulti));
> +	sg_init_one(sg, &vi->ctrl->allmulti, sizeof(vi->ctrl->allmulti));
>  
>  	if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_RX,
>  				  VIRTIO_NET_CTRL_RX_ALLMULTI, sg))
>  		dev_warn(&dev->dev, "Failed to %sable allmulti mode.\n",
> -			 vi->ctrl_allmulti ? "en" : "dis");
> +			 vi->ctrl->allmulti ? "en" : "dis");
>  
>  	uc_count = netdev_uc_count(dev);
>  	mc_count = netdev_mc_count(dev);
> @@ -1714,8 +1718,8 @@ static int virtnet_vlan_rx_add_vid(struct net_device *dev,
>  	struct virtnet_info *vi = netdev_priv(dev);
>  	struct scatterlist sg;
>  
> -	vi->ctrl_vid = vid;
> -	sg_init_one(&sg, &vi->ctrl_vid, sizeof(vi->ctrl_vid));
> +	vi->ctrl->vid = vid;
> +	sg_init_one(&sg, &vi->ctrl->vid, sizeof(vi->ctrl->vid));
>  
>  	if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_VLAN,
>  				  VIRTIO_NET_CTRL_VLAN_ADD, &sg))
> @@ -1729,8 +1733,8 @@ static int virtnet_vlan_rx_kill_vid(struct net_device *dev,
>  	struct virtnet_info *vi = netdev_priv(dev);
>  	struct scatterlist sg;
>  
> -	vi->ctrl_vid = vid;
> -	sg_init_one(&sg, &vi->ctrl_vid, sizeof(vi->ctrl_vid));
> +	vi->ctrl->vid = vid;
> +	sg_init_one(&sg, &vi->ctrl->vid, sizeof(vi->ctrl->vid));
>  
>  	if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_VLAN,
>  				  VIRTIO_NET_CTRL_VLAN_DEL, &sg))
> @@ -2126,9 +2130,9 @@ static int virtnet_restore_up(struct virtio_device *vdev)
>  static int virtnet_set_guest_offloads(struct virtnet_info *vi, u64 offloads)
>  {
>  	struct scatterlist sg;
> -	vi->ctrl_offloads = cpu_to_virtio64(vi->vdev, offloads);
> +	vi->ctrl->offloads = cpu_to_virtio64(vi->vdev, offloads);
>  
> -	sg_init_one(&sg, &vi->ctrl_offloads, sizeof(vi->ctrl_offloads));
> +	sg_init_one(&sg, &vi->ctrl->offloads, sizeof(vi->ctrl->offloads));
>  
>  	if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_GUEST_OFFLOADS,
>  				  VIRTIO_NET_CTRL_GUEST_OFFLOADS_SET, &sg)) {
> @@ -2351,6 +2355,7 @@ static void virtnet_free_queues(struct virtnet_info *vi)
>  
>  	kfree(vi->rq);
>  	kfree(vi->sq);
> +	kfree(vi->err_ctrl);
>  }
>  
>  static void _free_receive_bufs(struct virtnet_info *vi)
> @@ -2543,6 +2548,9 @@ static int virtnet_alloc_queues(struct virtnet_info *vi)
>  {
>  	int i;
>  
> +	vi->ctrl = kzalloc(sizeof(*vi->ctrl), GFP_KERNEL);
> +	if (!vi->ctrl)
> +		goto err_ctrl;
>  	vi->sq = kzalloc(sizeof(*vi->sq) * vi->max_queue_pairs, GFP_KERNEL);
>  	if (!vi->sq)
>  		goto err_sq;
> @@ -2571,6 +2579,8 @@ static int virtnet_alloc_queues(struct virtnet_info *vi)
>  err_rq:
>  	kfree(vi->sq);
>  err_sq:
> +	kfree(vq->ctrl);
> +err_ctrl:
>  	return -ENOMEM;
>  }
>  
> -- 
> MST