Subject: Re: [PATCH net] virtio-net: validate features during probe

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 19 Nov 2014 10:59:39 +0200

On Wed, Nov 19, 2014 at 02:35:39PM +0800, Jason Wang wrote:
> This patch validates feature dependencies during probe and fail the probing
> if a dependency is missed. This fixes the issues of hitting BUG()
> when qemu fails to advertise features correctly. One example is booting
> guest with ctrl_vq=off through qemu.
> 
> Cc: Rusty Russell <[email-masked]>
> Cc: Michael S. Tsirkin <[email-masked]>
> Cc: Cornelia Huck <[email-masked]>
> Cc: Wanlong Gao <[email-masked]>
> Signed-off-by: Jason Wang <[email-masked]>
> ---
>  drivers/net/virtio_net.c | 93 ++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 93 insertions(+)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index ec2a8b4..4a0ad46 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1673,6 +1673,95 @@ static const struct attribute_group virtio_net_mrg_rx_group = {
>  };
>  #endif
>  
> +static int virtnet_validate_features(struct virtio_device *dev,
> +				     unsigned int *table,
> +				     int table_size,
> +				     unsigned int feature)
> +{
> +	int i;
> +
> +	if (!virtio_has_feature(dev, feature)) {
> +		for (i = 0; i < table_size; i++) {
> +			unsigned int f = table[i];
> +
> +			if (virtio_has_feature(dev, f)) {
> +				dev_err(&dev->dev,
> +					"buggy hyperviser: feature 0x%x was advertised but its dependency 0x%x was not",

This line's way too long.

> +					f, feature);
> +				return -EINVAL;
> +			}
> +		}
> +	}
> +
> +	return 0;
> +}
> +
> +static int virtnet_check_features(struct virtio_device *dev)
> +{
> +	unsigned int features_for_ctrl_vq[] = {
> +		VIRTIO_NET_F_CTRL_RX,
> +		VIRTIO_NET_F_CTRL_VLAN,
> +		VIRTIO_NET_F_GUEST_ANNOUNCE,
> +		VIRTIO_NET_F_MQ,
> +		VIRTIO_NET_F_CTRL_MAC_ADDR
> +	};
> +	unsigned int features_for_guest_csum[] = {
> +		VIRTIO_NET_F_GUEST_TSO4,
> +		VIRTIO_NET_F_GUEST_TSO6,
> +		VIRTIO_NET_F_GUEST_ECN,
> +		VIRTIO_NET_F_GUEST_UFO,
> +	};
> +	unsigned int features_for_host_csum[] = {
> +		VIRTIO_NET_F_HOST_TSO4,
> +		VIRTIO_NET_F_HOST_TSO6,
> +		VIRTIO_NET_F_HOST_ECN,
> +		VIRTIO_NET_F_HOST_UFO,
> +	};
> +	int err;
> +
> +	err = virtnet_validate_features(dev, features_for_ctrl_vq,
> +					ARRAY_SIZE(features_for_ctrl_vq),
> +					VIRTIO_NET_F_CTRL_VQ);
> +	if (err)
> +		return err;
> +
> +	err = virtnet_validate_features(dev, features_for_guest_csum,
> +					ARRAY_SIZE(features_for_guest_csum),
> +					VIRTIO_NET_F_GUEST_CSUM);
> +	if (err)
> +		return err;
> +
> +	err = virtnet_validate_features(dev, features_for_host_csum,
> +					ARRAY_SIZE(features_for_host_csum),
> +					VIRTIO_NET_F_CSUM);
> +	if (err)
> +		return err;
> +
> +	if (virtio_has_feature(dev, VIRTIO_NET_F_GUEST_ECN) &&
> +	    (!virtio_has_feature(dev, VIRTIO_NET_F_GUEST_TSO4) ||
> +	     !virtio_has_feature(dev, VIRTIO_NET_F_GUEST_TSO6))) {
> +		dev_err(&dev->dev,
> +			"buggy hyperviser: feature 0x%x was advertised but its dependency 0x%x or 0x%x was not",
> +			VIRTIO_NET_F_GUEST_ECN,
> +			VIRTIO_NET_F_GUEST_TSO4,
> +			VIRTIO_NET_F_GUEST_TSO6);
> +		return -EINVAL;
> +	}
> +
> +	if (virtio_has_feature(dev, VIRTIO_NET_F_HOST_ECN) &&
> +	    (!virtio_has_feature(dev, VIRTIO_NET_F_HOST_TSO4) ||
> +	     !virtio_has_feature(dev, VIRTIO_NET_F_HOST_TSO6))) {
> +		dev_err(&dev->dev,
> +			"buggy hyperviser: feature 0x%x was advertised but its dependency 0x%x or 0x%x was not",
> +			VIRTIO_NET_F_HOST_ECN,
> +			VIRTIO_NET_F_HOST_TSO4,
> +			VIRTIO_NET_F_HOST_TSO6);
> +		return -EINVAL;
> +	}
> +
> +	return 0;

> +}
> +
>  static int virtnet_probe(struct virtio_device *vdev)
>  {
>  	int i, err;
> @@ -1680,6 +1769,10 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	struct virtnet_info *vi;
>  	u16 max_queue_pairs;
>  
> +	err = virtnet_check_features(vdev);
> +	if (err)
> +		return -EINVAL;
> +
>  	/* Find if host supports multiqueue virtio_net device */
>  	err = virtio_cread_feature(vdev, VIRTIO_NET_F_MQ,
>  				   struct virtio_net_config,

The API seems too complex, and you still had to open-code ECN logic.
Just open-code most of it.  You can use a helper macro to output a
friendly message without code duplication.
For example like the below (completely untested)?

I would also like to split things: dependencies on
VIRTIO_NET_F_CTRL_VQ might go into this kernel,
since they help fix BUG.

Others should wait since they don't fix any crashes, and there's a small
chance of a regression for some hypervisor in the field.

-->

virtio-net: friendlier handling of misconfigured hypervisors

We currently trigger BUG when VIRTIO_NET_F_CTRL_VQ
is not set but one of features depending on it is.
That's not a friendly way to report errors to
hypervisors.
Let's check, and fail probe instead.

Signed-off-by: Michael S. Tsirkin <[email-masked]>

---

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 26e1330..7a7d1a3 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1673,6 +1673,21 @@ static const struct attribute_group virtio_net_mrg_rx_group = {
 };
 #endif
 
+bool __virtnet_fail_on_feature(struct virtio_device *vdev, unsigned int fbit,
+			       const char *fname)
+{
+	if (!virtio_has_feature(vdev, fbit))
+		return false;
+
+        dev_err(&dev->dev, "missing requirements for feature bit %d: %s\n",
+		fbit, fname);
+
+	return true;
+}
+
+#define VIRTNET_FAIL_ON(vdev, fbit) \
+	__virtnet_fail_on_feature(vdev, fbit, #fbit)
+
 static int virtnet_probe(struct virtio_device *vdev)
 {
 	int i, err;
@@ -1680,6 +1695,14 @@ static int virtnet_probe(struct virtio_device *vdev)
 	struct virtnet_info *vi;
 	u16 max_queue_pairs;
 
+	if (!virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ) &&
+		(VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_CTRL_RX) ||
+		 VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_CTRL_VLAN) ||
+		 VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_GUEST_ANNOUNCE) ||
+		 VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_MQ) ||
+		 VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_CTRL_MAC_ADDR)))
+		return -EINVAL;
+
 	/* Find if host supports multiqueue virtio_net device */
 	err = virtio_cread_feature(vdev, VIRTIO_NET_F_MQ,
 				   struct virtio_net_config,