Linux Virtualization - Nov 2014 - [PATCH 1/2] virito: introduce methods of fixing device features

Buggy host may advertised buggy host features (a usual case is that host
advertise a feature whose dependencies were missed). In this case, driver
should detect and disable the buggy features by itself.

This patch introduces driver specific fix_features() method which is called
just before features finalizing to detect and disable buggy features
advertised by host.

Virtio-net will be the first user.

Cc: Rusty Russell <rusty at rustcorp.com.au>
Cc: Michael S. Tsirkin <mst at redhat.com>
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/virtio/virtio.c       |  4 ++++
 include/linux/virtio.h        |  1 +
 include/linux/virtio_config.h | 12 ++++++++++++
 3 files changed, 17 insertions(+)

diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index df598dd..7001d6e 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -181,6 +181,10 @@ static int virtio_dev_probe(struct device *_d)
 		if (device_features & (1 << i))
 			set_bit(i, dev->features);
 
+	/* Fix buggy features advertised by host */
+	if (drv->fix_features)
+		drv->fix_features(dev);
+
 	dev->config->finalize_features(dev);
 
 	err = drv->probe(dev);
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 65261a7..9d01b54 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -142,6 +142,7 @@ struct virtio_driver {
 	void (*scan)(struct virtio_device *dev);
 	void (*remove)(struct virtio_device *dev);
 	void (*config_changed)(struct virtio_device *dev);
+	void (*fix_features)(struct virtio_device *dev);
 #ifdef CONFIG_PM
 	int (*freeze)(struct virtio_device *dev);
 	int (*restore)(struct virtio_device *dev);
diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index 7f4ef66..7bd89ea 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -96,6 +96,18 @@ static inline bool virtio_has_feature(const struct
virtio_device *vdev,
 	return test_bit(fbit, vdev->features);
 }
 
+static inline void virtio_disable_feature(struct virtio_device *vdev,
+                                          unsigned int fbit)
+{
+	BUG_ON(fbit >= VIRTIO_TRANSPORT_F_START);
+	BUG_ON(vdev->config->get_status(vdev) &
+	       ~(VIRTIO_CONFIG_S_ACKNOWLEDGE | VIRTIO_CONFIG_S_DRIVER));
+
+	virtio_check_driver_offered_feature(vdev, fbit);
+
+	clear_bit(fbit, vdev->features);
+}
+
 static inline
 struct virtqueue *virtio_find_single_vq(struct virtio_device *vdev,
 					vq_callback_t *c, const char *n)
-- 
1.9.1

This patch tries to detect the possible buggy features advertised by host
and fix them. One example is current booting virtio-net with only
ctrl_vq disabled, qemu may still advertise many features which depends
it. This will trigger several BUG()s in virtnet_send_command().

This patch utilizes the fix_features() method, and disable all features that
depends on ctrl_vq if it was not advertised.

This fixes the crash when booting with ctrl_vq=off.

Cc: Rusty Russell <rusty at rustcorp.com.au>
Cc: Michael S. Tsirkin <mst at redhat.com>
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/net/virtio_net.c | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index ec2a8b4..d6bb5fa 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1948,6 +1948,40 @@ static int virtnet_restore(struct virtio_device *vdev)
 }
 #endif
 
+static void virtnet_fix_features(struct virtio_device *dev)
+{
+	if (!virtio_has_feature(dev, VIRTIO_NET_F_CTRL_VQ)) {
+		if (virtio_has_feature(dev, VIRTIO_NET_F_CTRL_RX)) {
+			pr_warning("Disable VIRTIO_NET_F_CTRL_RX since host "
+				   "does not advertise VIRTIO_NET_F_CTRL_VQ");
+			virtio_disable_feature(dev, VIRTIO_NET_F_CTRL_RX);
+		}
+		if (virtio_has_feature(dev, VIRTIO_NET_F_CTRL_VLAN)) {
+			pr_warning("Disable VIRTIO_NET_F_CTRL_VLAN since host "
+				   "does not advertise VIRTIO_NET_F_CTRL_VQ");
+			virtio_disable_feature(dev, VIRTIO_NET_F_CTRL_VLAN);
+		}
+		if (virtio_has_feature(dev, VIRTIO_NET_F_GUEST_ANNOUNCE)) {
+			pr_warning("Disable VIRTIO_NET_F_GUEST_ANNOUCE since "
+				   "host does not advertise "
+				   "VIRTIO_NET_F_CTRL_VQ");
+			virtio_disable_feature(dev,
+					       VIRTIO_NET_F_GUEST_ANNOUNCE);
+		}
+		if (virtio_has_feature(dev, VIRTIO_NET_F_MQ)) {
+			pr_warning("Disable VIRTIO_NET_F_MQ since host "
+				   "does not advertise VIRTIO_NET_F_CTRL_VQ");
+			virtio_disable_feature(dev, VIRTIO_NET_F_CTRL_VLAN);
+		}
+		if (virtio_has_feature(dev, VIRTIO_NET_F_CTRL_MAC_ADDR)) {
+			pr_warning("Disable VIRTIO_NET_F_CTRL_MAC_ADDR since "
+				   "host does not advertise "
+				   "VIRTIO_NET_F_CTRL_VQ");
+			virtio_disable_feature(dev, VIRTIO_NET_F_CTRL_VLAN);
+		}
+	}
+}
+
 static struct virtio_device_id id_table[] = {
 	{ VIRTIO_ID_NET, VIRTIO_DEV_ANY_ID },
 	{ 0 },
@@ -1975,6 +2009,7 @@ static struct virtio_driver virtio_net_driver = {
 	.probe =	virtnet_probe,
 	.remove =	virtnet_remove,
 	.config_changed = virtnet_config_changed,
+	.fix_features = virtnet_fix_features,
 #ifdef CONFIG_PM_SLEEP
 	.freeze =	virtnet_freeze,
 	.restore =	virtnet_restore,
-- 
1.9.1

On 11/13/2014 01:24 PM, Jason Wang wrote:
> This patch tries to detect the possible buggy features advertised by host
> and fix them. One example is current booting virtio-net with only
> ctrl_vq disabled, qemu may still advertise many features which depends
> it. This will trigger several BUG()s in virtnet_send_command().
>
> This patch utilizes the fix_features() method, and disable all features
that
> depends on ctrl_vq if it was not advertised.
>
> This fixes the crash when booting with ctrl_vq=off.
>
> Cc: Rusty Russell <rusty at rustcorp.com.au>
> Cc: Michael S. Tsirkin <mst at redhat.com>
> Signed-off-by: Jason Wang <jasowang at redhat.com>
> ---
>  drivers/net/virtio_net.c | 35 +++++++++++++++++++++++++++++++++++
>  1 file changed, 35 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index ec2a8b4..d6bb5fa 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1948,6 +1948,40 @@ static int virtnet_restore(struct virtio_device
*vdev)
>  }
>  #endif
>  
> +static void virtnet_fix_features(struct virtio_device *dev)
> +{
> +	if (!virtio_has_feature(dev, VIRTIO_NET_F_CTRL_VQ)) {
> +		if (virtio_has_feature(dev, VIRTIO_NET_F_CTRL_RX)) {
> +			pr_warning("Disable VIRTIO_NET_F_CTRL_RX since host "
> +				   "does not advertise VIRTIO_NET_F_CTRL_VQ");
> +			virtio_disable_feature(dev, VIRTIO_NET_F_CTRL_RX);
> +		}
> +		if (virtio_has_feature(dev, VIRTIO_NET_F_CTRL_VLAN)) {
> +			pr_warning("Disable VIRTIO_NET_F_CTRL_VLAN since host "
> +				   "does not advertise VIRTIO_NET_F_CTRL_VQ");
> +			virtio_disable_feature(dev, VIRTIO_NET_F_CTRL_VLAN);
> +		}
> +		if (virtio_has_feature(dev, VIRTIO_NET_F_GUEST_ANNOUNCE)) {
> +			pr_warning("Disable VIRTIO_NET_F_GUEST_ANNOUCE since "
> +				   "host does not advertise "
> +				   "VIRTIO_NET_F_CTRL_VQ");
> +			virtio_disable_feature(dev,
> +					       VIRTIO_NET_F_GUEST_ANNOUNCE);
> +		}
> +		if (virtio_has_feature(dev, VIRTIO_NET_F_MQ)) {
> +			pr_warning("Disable VIRTIO_NET_F_MQ since host "
> +				   "does not advertise VIRTIO_NET_F_CTRL_VQ");
> +			virtio_disable_feature(dev, VIRTIO_NET_F_CTRL_VLAN);
> +		}
> +		if (virtio_has_feature(dev, VIRTIO_NET_F_CTRL_MAC_ADDR)) {
> +			pr_warning("Disable VIRTIO_NET_F_CTRL_MAC_ADDR since "
> +				   "host does not advertise "
> +				   "VIRTIO_NET_F_CTRL_VQ");
> +			virtio_disable_feature(dev, VIRTIO_NET_F_CTRL_VLAN);
Oops, this looks like a cut-and-paste error. Will post
V2.
> +		}
> +	}
> +}
> +
>  static struct virtio_device_id id_table[] = {
>  	{ VIRTIO_ID_NET, VIRTIO_DEV_ANY_ID },
>  	{ 0 },
> @@ -1975,6 +2009,7 @@ static struct virtio_driver virtio_net_driver = {
>  	.probe =	virtnet_probe,
>  	.remove =	virtnet_remove,
>  	.config_changed = virtnet_config_changed,
> +	.fix_features = virtnet_fix_features,
>  #ifdef CONFIG_PM_SLEEP
>  	.freeze =	virtnet_freeze,
>  	.restore =	virtnet_restore,