[PATCH V3 1/2] virtio: introduce methods of sanitizing device features

[PATCH V3 1/2] virtio: introduce methods of sanitizing device features

[Jason Wang]

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 sanitize_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@rustcorp.com.au>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
Cc: Wanlong Gao <gaowanlong@cn.fujitsu.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
Changes from V2:
- fix typo
- rename fix_features to sanitize_features
---
 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..6a86b4f 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);
 
+	/* Sanitize buggy features advertised by host */
+	if (drv->sanitize_features)
+		drv->sanitize_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..5aed283 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 (*sanitize_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

[PATCH V3 2/2] virtio-net: sanitize buggy features advertised by host

[Jason Wang]

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

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

This fixes the crash when booting with ctrl_vq=off using qemu.

Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
Cc: Wanlong Gao <gaowanlong@cn.fujitsu.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
Changes from V1:
- fix the cut-and-paste error
Changes from V2:
- loop through an array of feature bits
- switch to use dev_warn()
---
 drivers/net/virtio_net.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index ec2a8b4..6fadd8c 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1948,6 +1948,31 @@ static int virtnet_restore(struct virtio_device *vdev)
 }
 #endif
 
+static void virtnet_sanitize_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
+	};
+	int i;
+
+	if (!virtio_has_feature(dev, VIRTIO_NET_F_CTRL_VQ)) {
+		for (i = 0; i < ARRAY_SIZE(features_for_ctrl_vq); i++) {
+			unsigned int f = features_for_ctrl_vq[i];
+			if (virtio_has_feature(dev, f)) {
+				virtio_disable_feature(dev, f);
+				dev_warn(&dev->dev,
+					 "buggy hyperviser: disable feature "
+					 "0x%x since VIRTIO_NET_F_CTRL_VQ was "
+					 "not advertised.\n", f);
+			}
+		}
+	}
+}
+
 static struct virtio_device_id id_table[] = {
 	{ VIRTIO_ID_NET, VIRTIO_DEV_ANY_ID },
 	{ 0 },
@@ -1975,6 +2000,7 @@ static struct virtio_driver virtio_net_driver = {
 	.probe =	virtnet_probe,
 	.remove =	virtnet_remove,
 	.config_changed = virtnet_config_changed,
+	.sanitize_features = virtnet_sanitize_features,
 #ifdef CONFIG_PM_SLEEP
 	.freeze =	virtnet_freeze,
 	.restore =	virtnet_restore,
-- 
1.9.1

Re: [PATCH V3 2/2] virtio-net: sanitize buggy features advertised by host

[Michael S. Tsirkin]

On Mon, Nov 17, 2014 at 05:17:18PM +0800, Jason Wang wrote:
> This patch tries to detect the possible buggy features advertised by host
> and sanitize them. One example is booting virtio-net with only ctrl_vq
> disabled, qemu may still advertise many features which depends on it. This
> will trigger several BUG()s in virtnet_send_command().
> 
> This patch utilizes the sanitize_features() method, and disables all
> features that depends on ctrl_vq if it was not advertised.
> 
> This fixes the crash when booting with ctrl_vq=off using qemu.
> 
> Cc: Rusty Russell <rusty@rustcorp.com.au>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
> Cc: Wanlong Gao <gaowanlong@cn.fujitsu.com>
> Signed-off-by: Jason Wang <jasowang@redhat.com>


So I'm not sure this is useful.
The spec says:
	The device MUST NOT offer a feature which requires another feature which
	was not offered.
So this is a buggy hypervisor, and I believe we should just fail probe.
This can be done without crashing, and is generally a better
idea that second-guessing what hypervisor wants us to do.





However, assuming that we do want this change:
This can be replaced with a table driven design in virtio core, but
since you chose to open code it, I would drop table below altogether.


Just make it
	if (!virtio_has_feature(dev, VIRTIO_NET_F_CTRL_VQ)) {
		virtio_disable_feature(dev, VIRTIO_NET_F_CTRL_RX);
		virtio_disable_feature(dev, VIRTIO_NET_F_CTRL_VLAN);
		virtio_disable_feature(dev, VIRTIO_NET_F_GUEST_ANNOUNCE);
		virtio_disable_feature(dev, VIRTIO_NET_F_MQ);
		virtio_disable_feature(dev, VIRTIO_NET_F_CTRL_MAC_ADDR);
	}




> ---
> Changes from V1:
> - fix the cut-and-paste error
> Changes from V2:
> - loop through an array of feature bits
> - switch to use dev_warn()
> ---
>  drivers/net/virtio_net.c | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index ec2a8b4..6fadd8c 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1948,6 +1948,31 @@ static int virtnet_restore(struct virtio_device *vdev)
>  }
>  #endif
>  
> +static void virtnet_sanitize_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
> +	};

This is not the only dependency: checksums
have dependencies too. See virtio 1.0 spec.



> +	int i;
> +
> +	if (!virtio_has_feature(dev, VIRTIO_NET_F_CTRL_VQ)) {
> +		for (i = 0; i < ARRAY_SIZE(features_for_ctrl_vq); i++) {
> +			unsigned int f = features_for_ctrl_vq[i];
> +			if (virtio_has_feature(dev, f)) {
> +				virtio_disable_feature(dev, f);
> +				dev_warn(&dev->dev,
> +					 "buggy hyperviser: disable feature "
> +					 "0x%x since VIRTIO_NET_F_CTRL_VQ was "
> +					 "not advertised.\n", f);
> +			}
> +		}
> +	}
> +}
> +
>  static struct virtio_device_id id_table[] = {
>  	{ VIRTIO_ID_NET, VIRTIO_DEV_ANY_ID },
>  	{ 0 },
> @@ -1975,6 +2000,7 @@ static struct virtio_driver virtio_net_driver = {
>  	.probe =	virtnet_probe,
>  	.remove =	virtnet_remove,
>  	.config_changed = virtnet_config_changed,
> +	.sanitize_features = virtnet_sanitize_features,
>  #ifdef CONFIG_PM_SLEEP
>  	.freeze =	virtnet_freeze,
>  	.restore =	virtnet_restore,
> -- 
> 1.9.1

Re: [PATCH V3 2/2] virtio-net: sanitize buggy features advertised by host

[Jason Wang]

On 11/17/2014 06:08 PM, Michael S. Tsirkin wrote:
> On Mon, Nov 17, 2014 at 05:17:18PM +0800, Jason Wang wrote:
>> This patch tries to detect the possible buggy features advertised by host
>> and sanitize them. One example is booting virtio-net with only ctrl_vq
>> disabled, qemu may still advertise many features which depends on it. This
>> will trigger several BUG()s in virtnet_send_command().
>>
>> This patch utilizes the sanitize_features() method, and disables all
>> features that depends on ctrl_vq if it was not advertised.
>>
>> This fixes the crash when booting with ctrl_vq=off using qemu.
>>
>> Cc: Rusty Russell <rusty@rustcorp.com.au>
>> Cc: Michael S. Tsirkin <mst@redhat.com>
>> Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
>> Cc: Wanlong Gao <gaowanlong@cn.fujitsu.com>
>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>
> So I'm not sure this is useful.
> The spec says:
> 	The device MUST NOT offer a feature which requires another feature which
> 	was not offered.

We can't guarantee that hypervisor's implementation are 100% correct.
> So this is a buggy hypervisor, and I believe we should just fail probe.
> This can be done without crashing, and is generally a better
> idea that second-guessing what hypervisor wants us to do.
>

So we still need something like this patch to detect the wrong
dependencies. And the features fixing like this is not something new,
see how net device fix the features through ndo_fix_features().
>
>
>
> However, assuming that we do want this change:
> This can be replaced with a table driven design in virtio core, but
> since you chose to open code it, I would drop table below altogether.
>
>
> Just make it
> 	if (!virtio_has_feature(dev, VIRTIO_NET_F_CTRL_VQ)) {
> 		virtio_disable_feature(dev, VIRTIO_NET_F_CTRL_RX);
> 		virtio_disable_feature(dev, VIRTIO_NET_F_CTRL_VLAN);
> 		virtio_disable_feature(dev, VIRTIO_NET_F_GUEST_ANNOUNCE);
> 		virtio_disable_feature(dev, VIRTIO_NET_F_MQ);
> 		virtio_disable_feature(dev, VIRTIO_NET_F_CTRL_MAC_ADDR);
> 	}
>

This is similar to what I did in v1 and v2. Either are ok for me.
>
>
>> ---
>> Changes from V1:
>> - fix the cut-and-paste error
>> Changes from V2:
>> - loop through an array of feature bits
>> - switch to use dev_warn()
>> ---
>>  drivers/net/virtio_net.c | 26 ++++++++++++++++++++++++++
>>  1 file changed, 26 insertions(+)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index ec2a8b4..6fadd8c 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -1948,6 +1948,31 @@ static int virtnet_restore(struct virtio_device *vdev)
>>  }
>>  #endif
>>  
>> +static void virtnet_sanitize_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
>> +	};
> This is not the only dependency: checksums
> have dependencies too. See virtio 1.0 spec.
>

I see ,and this kind of check could be added. But we're really safe
since qemu handle such cases and won't advertise any offload feature is
csum is not supported.
>
>> +	int i;
>> +
>> +	if (!virtio_has_feature(dev, VIRTIO_NET_F_CTRL_VQ)) {
>> +		for (i = 0; i < ARRAY_SIZE(features_for_ctrl_vq); i++) {
>> +			unsigned int f = features_for_ctrl_vq[i];
>> +			if (virtio_has_feature(dev, f)) {
>> +				virtio_disable_feature(dev, f);
>> +				dev_warn(&dev->dev,
>> +					 "buggy hyperviser: disable feature "
>> +					 "0x%x since VIRTIO_NET_F_CTRL_VQ was "
>> +					 "not advertised.\n", f);
>> +			}
>> +		}
>> +	}
>> +}
>> +
>>  static struct virtio_device_id id_table[] = {
>>  	{ VIRTIO_ID_NET, VIRTIO_DEV_ANY_ID },
>>  	{ 0 },
>> @@ -1975,6 +2000,7 @@ static struct virtio_driver virtio_net_driver = {
>>  	.probe =	virtnet_probe,
>>  	.remove =	virtnet_remove,
>>  	.config_changed = virtnet_config_changed,
>> +	.sanitize_features = virtnet_sanitize_features,
>>  #ifdef CONFIG_PM_SLEEP
>>  	.freeze =	virtnet_freeze,
>>  	.restore =	virtnet_restore,
>> -- 
>> 1.9.1
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/

Re: [PATCH V3 2/2] virtio-net: sanitize buggy features advertised by host

[Michael S. Tsirkin]

On Tue, Nov 18, 2014 at 11:03:32AM +0800, Jason Wang wrote:
> On 11/17/2014 06:08 PM, Michael S. Tsirkin wrote:
> > On Mon, Nov 17, 2014 at 05:17:18PM +0800, Jason Wang wrote:
> >> This patch tries to detect the possible buggy features advertised by host
> >> and sanitize them. One example is booting virtio-net with only ctrl_vq
> >> disabled, qemu may still advertise many features which depends on it. This
> >> will trigger several BUG()s in virtnet_send_command().
> >>
> >> This patch utilizes the sanitize_features() method, and disables all
> >> features that depends on ctrl_vq if it was not advertised.
> >>
> >> This fixes the crash when booting with ctrl_vq=off using qemu.
> >>
> >> Cc: Rusty Russell <rusty@rustcorp.com.au>
> >> Cc: Michael S. Tsirkin <mst@redhat.com>
> >> Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
> >> Cc: Wanlong Gao <gaowanlong@cn.fujitsu.com>
> >> Signed-off-by: Jason Wang <jasowang@redhat.com>
> >
> > So I'm not sure this is useful.
> > The spec says:
> > 	The device MUST NOT offer a feature which requires another feature which
> > 	was not offered.
> 
> We can't guarantee that hypervisor's implementation are 100% correct.
> > So this is a buggy hypervisor, and I believe we should just fail probe.
> > This can be done without crashing, and is generally a better
> > idea that second-guessing what hypervisor wants us to do.
> >
> 
> So we still need something like this patch to detect the wrong
> dependencies. And the features fixing like this is not something new,
> see how net device fix the features through ndo_fix_features().

I think that's different. If linux refuses to work with a broken
hardware NIC, you can not do anything, and hardware is mass-produced so
we know many people are affected.
If linux refuses to work with a misconfigured hypervisor, it's just one
user who misconfigured it, and hypervisor can be fixed.

So let's not work around bugs at least unless we know that many people
already use a broken hypervisor, something prevents vendor from fixing it.


> >
> >
> >
> > However, assuming that we do want this change:
> > This can be replaced with a table driven design in virtio core, but
> > since you chose to open code it, I would drop table below altogether.
> >
> >
> > Just make it
> > 	if (!virtio_has_feature(dev, VIRTIO_NET_F_CTRL_VQ)) {
> > 		virtio_disable_feature(dev, VIRTIO_NET_F_CTRL_RX);
> > 		virtio_disable_feature(dev, VIRTIO_NET_F_CTRL_VLAN);
> > 		virtio_disable_feature(dev, VIRTIO_NET_F_GUEST_ANNOUNCE);
> > 		virtio_disable_feature(dev, VIRTIO_NET_F_MQ);
> > 		virtio_disable_feature(dev, VIRTIO_NET_F_CTRL_MAC_ADDR);
> > 	}
> >
> 
> This is similar to what I did in v1 and v2. Either are ok for me.
> >
> >
> >> ---
> >> Changes from V1:
> >> - fix the cut-and-paste error
> >> Changes from V2:
> >> - loop through an array of feature bits
> >> - switch to use dev_warn()
> >> ---
> >>  drivers/net/virtio_net.c | 26 ++++++++++++++++++++++++++
> >>  1 file changed, 26 insertions(+)
> >>
> >> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> >> index ec2a8b4..6fadd8c 100644
> >> --- a/drivers/net/virtio_net.c
> >> +++ b/drivers/net/virtio_net.c
> >> @@ -1948,6 +1948,31 @@ static int virtnet_restore(struct virtio_device *vdev)
> >>  }
> >>  #endif
> >>  
> >> +static void virtnet_sanitize_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
> >> +	};
> > This is not the only dependency: checksums
> > have dependencies too. See virtio 1.0 spec.
> >
> 
> I see ,and this kind of check could be added. But we're really safe
> since qemu handle such cases and won't advertise any offload feature is
> csum is not supported.
> >
> >> +	int i;
> >> +
> >> +	if (!virtio_has_feature(dev, VIRTIO_NET_F_CTRL_VQ)) {
> >> +		for (i = 0; i < ARRAY_SIZE(features_for_ctrl_vq); i++) {
> >> +			unsigned int f = features_for_ctrl_vq[i];
> >> +			if (virtio_has_feature(dev, f)) {
> >> +				virtio_disable_feature(dev, f);
> >> +				dev_warn(&dev->dev,
> >> +					 "buggy hyperviser: disable feature "
> >> +					 "0x%x since VIRTIO_NET_F_CTRL_VQ was "
> >> +					 "not advertised.\n", f);
> >> +			}
> >> +		}
> >> +	}
> >> +}
> >> +
> >>  static struct virtio_device_id id_table[] = {
> >>  	{ VIRTIO_ID_NET, VIRTIO_DEV_ANY_ID },
> >>  	{ 0 },
> >> @@ -1975,6 +2000,7 @@ static struct virtio_driver virtio_net_driver = {
> >>  	.probe =	virtnet_probe,
> >>  	.remove =	virtnet_remove,
> >>  	.config_changed = virtnet_config_changed,
> >> +	.sanitize_features = virtnet_sanitize_features,
> >>  #ifdef CONFIG_PM_SLEEP
> >>  	.freeze =	virtnet_freeze,
> >>  	.restore =	virtnet_restore,
> >> -- 
> >> 1.9.1
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > Please read the FAQ at  http://www.tux.org/lkml/

Re: [PATCH V3 1/2] virtio: introduce methods of sanitizing device features

[Michael S. Tsirkin]

On Mon, Nov 17, 2014 at 05:17:17PM +0800, Jason Wang wrote:
> 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 sanitize_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@rustcorp.com.au>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
> Cc: Wanlong Gao <gaowanlong@cn.fujitsu.com>
> Signed-off-by: Jason Wang <jasowang@redhat.com>

Hmm this conflicts with virtio 1.0 work: we drop
features as bitmap there.

> ---
> Changes from V2:
> - fix typo
> - rename fix_features to sanitize_features
> ---
>  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..6a86b4f 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);
>  
> +	/* Sanitize buggy features advertised by host */
> +	if (drv->sanitize_features)
> +		drv->sanitize_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..5aed283 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 (*sanitize_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

Re: [PATCH V3 1/2] virtio: introduce methods of sanitizing device features

[Cornelia Huck]

On Mon, 17 Nov 2014 11:37:01 +0200
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Mon, Nov 17, 2014 at 05:17:17PM +0800, Jason Wang wrote:
> > 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 sanitize_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@rustcorp.com.au>
> > Cc: Michael S. Tsirkin <mst@redhat.com>
> > Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
> > Cc: Wanlong Gao <gaowanlong@cn.fujitsu.com>
> > Signed-off-by: Jason Wang <jasowang@redhat.com>
> 
> Hmm this conflicts with virtio 1.0 work: we drop
> features as bitmap there.

But that's an implementation detail, no? We'll still need a way for the
driver to sanitize features, and I think this interface works just fine.

Re: [PATCH V3 1/2] virtio: introduce methods of sanitizing device features

[Michael S. Tsirkin]

On Mon, Nov 17, 2014 at 10:44:30AM +0100, Cornelia Huck wrote:
> On Mon, 17 Nov 2014 11:37:01 +0200
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
> > On Mon, Nov 17, 2014 at 05:17:17PM +0800, Jason Wang wrote:
> > > 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 sanitize_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@rustcorp.com.au>
> > > Cc: Michael S. Tsirkin <mst@redhat.com>
> > > Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
> > > Cc: Wanlong Gao <gaowanlong@cn.fujitsu.com>
> > > Signed-off-by: Jason Wang <jasowang@redhat.com>
> > 
> > Hmm this conflicts with virtio 1.0 work: we drop
> > features as bitmap there.
> 
> But that's an implementation detail, no? We'll still need a way for the
> driver to sanitize features, and I think this interface works just fine.

Now that you mention it, I don't think we do.

The spec is quite explicit that devices must not expose invalid
combinations of features.

Admittedly, BUG_ON isn't very friendly to hypervisors.

But e.g. failing probe seems better than trying to work around
hypervisor bugs - otherwise we'll be stuck maintaining compatibility
with hypervisors forever.

-- 
MST

Re: [PATCH V3 1/2] virtio: introduce methods of sanitizing device features

[Cornelia Huck]

On Mon, 17 Nov 2014 12:11:39 +0200
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Mon, Nov 17, 2014 at 10:44:30AM +0100, Cornelia Huck wrote:
> > On Mon, 17 Nov 2014 11:37:01 +0200
> > "Michael S. Tsirkin" <mst@redhat.com> wrote:
> > 
> > > On Mon, Nov 17, 2014 at 05:17:17PM +0800, Jason Wang wrote:
> > > > 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 sanitize_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@rustcorp.com.au>
> > > > Cc: Michael S. Tsirkin <mst@redhat.com>
> > > > Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
> > > > Cc: Wanlong Gao <gaowanlong@cn.fujitsu.com>
> > > > Signed-off-by: Jason Wang <jasowang@redhat.com>
> > > 
> > > Hmm this conflicts with virtio 1.0 work: we drop
> > > features as bitmap there.
> > 
> > But that's an implementation detail, no? We'll still need a way for the
> > driver to sanitize features, and I think this interface works just fine.
> 
> Now that you mention it, I don't think we do.
> 
> The spec is quite explicit that devices must not expose invalid
> combinations of features.

Unfortunately, this does not ensure that there won't be buggy
hypervisors out there, just as there's buggy hardware floating around.

> 
> Admittedly, BUG_ON isn't very friendly to hypervisors.
> 
> But e.g. failing probe seems better than trying to work around
> hypervisor bugs - otherwise we'll be stuck maintaining compatibility
> with hypervisors forever.

Good point. Failing probe is still much better than hitting BUG_ONs.

We'll still need a driver callback, though, that can return an error on
bogus feature bit combinations.

Re: [PATCH V3 1/2] virtio: introduce methods of sanitizing device features

[Michael S. Tsirkin]

On Mon, Nov 17, 2014 at 11:20:48AM +0100, Cornelia Huck wrote:
> On Mon, 17 Nov 2014 12:11:39 +0200
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
> > On Mon, Nov 17, 2014 at 10:44:30AM +0100, Cornelia Huck wrote:
> > > On Mon, 17 Nov 2014 11:37:01 +0200
> > > "Michael S. Tsirkin" <mst@redhat.com> wrote:
> > > 
> > > > On Mon, Nov 17, 2014 at 05:17:17PM +0800, Jason Wang wrote:
> > > > > 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 sanitize_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@rustcorp.com.au>
> > > > > Cc: Michael S. Tsirkin <mst@redhat.com>
> > > > > Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
> > > > > Cc: Wanlong Gao <gaowanlong@cn.fujitsu.com>
> > > > > Signed-off-by: Jason Wang <jasowang@redhat.com>
> > > > 
> > > > Hmm this conflicts with virtio 1.0 work: we drop
> > > > features as bitmap there.
> > > 
> > > But that's an implementation detail, no? We'll still need a way for the
> > > driver to sanitize features, and I think this interface works just fine.
> > 
> > Now that you mention it, I don't think we do.
> > 
> > The spec is quite explicit that devices must not expose invalid
> > combinations of features.
> 
> Unfortunately, this does not ensure that there won't be buggy
> hypervisors out there, just as there's buggy hardware floating around.
> 
> > 
> > Admittedly, BUG_ON isn't very friendly to hypervisors.
> > 
> > But e.g. failing probe seems better than trying to work around
> > hypervisor bugs - otherwise we'll be stuck maintaining compatibility
> > with hypervisors forever.
> 
> Good point. Failing probe is still much better than hitting BUG_ONs.
> 
> We'll still need a driver callback, though, that can return an error on
> bogus feature bit combinations.

Why bother?  Just check features at start of probe, and return an error.

-- 
MST

Re: [PATCH V3 1/2] virtio: introduce methods of sanitizing device features

[Cornelia Huck]

On Mon, 17 Nov 2014 12:28:49 +0200
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Mon, Nov 17, 2014 at 11:20:48AM +0100, Cornelia Huck wrote:
> > On Mon, 17 Nov 2014 12:11:39 +0200
> > "Michael S. Tsirkin" <mst@redhat.com> wrote:
> > 
> > > On Mon, Nov 17, 2014 at 10:44:30AM +0100, Cornelia Huck wrote:
> > > > On Mon, 17 Nov 2014 11:37:01 +0200
> > > > "Michael S. Tsirkin" <mst@redhat.com> wrote:
> > > > 
> > > > > On Mon, Nov 17, 2014 at 05:17:17PM +0800, Jason Wang wrote:
> > > > > > 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 sanitize_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@rustcorp.com.au>
> > > > > > Cc: Michael S. Tsirkin <mst@redhat.com>
> > > > > > Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
> > > > > > Cc: Wanlong Gao <gaowanlong@cn.fujitsu.com>
> > > > > > Signed-off-by: Jason Wang <jasowang@redhat.com>
> > > > > 
> > > > > Hmm this conflicts with virtio 1.0 work: we drop
> > > > > features as bitmap there.
> > > > 
> > > > But that's an implementation detail, no? We'll still need a way for the
> > > > driver to sanitize features, and I think this interface works just fine.
> > > 
> > > Now that you mention it, I don't think we do.
> > > 
> > > The spec is quite explicit that devices must not expose invalid
> > > combinations of features.
> > 
> > Unfortunately, this does not ensure that there won't be buggy
> > hypervisors out there, just as there's buggy hardware floating around.
> > 
> > > 
> > > Admittedly, BUG_ON isn't very friendly to hypervisors.
> > > 
> > > But e.g. failing probe seems better than trying to work around
> > > hypervisor bugs - otherwise we'll be stuck maintaining compatibility
> > > with hypervisors forever.
> > 
> > Good point. Failing probe is still much better than hitting BUG_ONs.
> > 
> > We'll still need a driver callback, though, that can return an error on
> > bogus feature bit combinations.
> 
> Why bother?  Just check features at start of probe, and return an error.

So we'd fail probing due to bogus features after setting FEATURES_OK in
the virtio-1 case, won't we? Feels a bit weird, but seems to be covered
by the spec.

Re: [PATCH V3 1/2] virtio: introduce methods of sanitizing device features

[Jason Wang]

On 11/17/2014 06:11 PM, Michael S. Tsirkin wrote:
> On Mon, Nov 17, 2014 at 10:44:30AM +0100, Cornelia Huck wrote:
>> On Mon, 17 Nov 2014 11:37:01 +0200
>> "Michael S. Tsirkin" <mst@redhat.com> wrote:
>>
>>> On Mon, Nov 17, 2014 at 05:17:17PM +0800, Jason Wang wrote:
>>>> 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 sanitize_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@rustcorp.com.au>
>>>> Cc: Michael S. Tsirkin <mst@redhat.com>
>>>> Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
>>>> Cc: Wanlong Gao <gaowanlong@cn.fujitsu.com>
>>>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>>> Hmm this conflicts with virtio 1.0 work: we drop
>>> features as bitmap there.
>> But that's an implementation detail, no? We'll still need a way for the
>> driver to sanitize features, and I think this interface works just fine.
> Now that you mention it, I don't think we do.
>
> The spec is quite explicit that devices must not expose invalid
> combinations of features.
>
> Admittedly, BUG_ON isn't very friendly to hypervisors.
>
> But e.g. failing probe seems better than trying to work around
> hypervisor bugs - otherwise we'll be stuck maintaining compatibility
> with hypervisors forever.
>

I'm ok with failing the probe.

But it won't cost big effort to workaround only features dependencies
issue. I don't see how this block any further features implementation.
Looking at virtio-net, it also depends on network core to fix NETIF_F_*
dependencies.

There seems no way to get rid of maintaining compatibility, e.g  the
workarounds for the buggy hypervisor without VIRTIO_F_ANY_LAYOUT support.

Re: [PATCH V3 1/2] virtio: introduce methods of sanitizing device features

[Michael S. Tsirkin]

On Tue, Nov 18, 2014 at 11:23:49AM +0800, Jason Wang wrote:
> On 11/17/2014 06:11 PM, Michael S. Tsirkin wrote:
> > On Mon, Nov 17, 2014 at 10:44:30AM +0100, Cornelia Huck wrote:
> >> On Mon, 17 Nov 2014 11:37:01 +0200
> >> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> >>
> >>> On Mon, Nov 17, 2014 at 05:17:17PM +0800, Jason Wang wrote:
> >>>> 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 sanitize_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@rustcorp.com.au>
> >>>> Cc: Michael S. Tsirkin <mst@redhat.com>
> >>>> Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
> >>>> Cc: Wanlong Gao <gaowanlong@cn.fujitsu.com>
> >>>> Signed-off-by: Jason Wang <jasowang@redhat.com>
> >>> Hmm this conflicts with virtio 1.0 work: we drop
> >>> features as bitmap there.
> >> But that's an implementation detail, no? We'll still need a way for the
> >> driver to sanitize features, and I think this interface works just fine.
> > Now that you mention it, I don't think we do.
> >
> > The spec is quite explicit that devices must not expose invalid
> > combinations of features.
> >
> > Admittedly, BUG_ON isn't very friendly to hypervisors.
> >
> > But e.g. failing probe seems better than trying to work around
> > hypervisor bugs - otherwise we'll be stuck maintaining compatibility
> > with hypervisors forever.
> >
> 
> I'm ok with failing the probe.
> 
> But it won't cost big effort to workaround only features dependencies
> issue.

>From experience, second-guessing user always adds maintainance.

> I don't see how this block any further features implementation.
> Looking at virtio-net, it also depends on network core to fix NETIF_F_*
> dependencies.

That code is common for all drivers, so it was moved to core.

> There seems no way to get rid of maintaining compatibility, e.g  the
> workarounds for the buggy hypervisor without VIRTIO_F_ANY_LAYOUT support.

Right - because too many hypervisors shipped without it, it's too
much work to fix them all.
No such motivation here, right?

-- 
MST

Re: [PATCH V3 1/2] virtio: introduce methods of sanitizing device features

[Jason Wang]

On 11/18/2014 07:04 PM, Michael S. Tsirkin wrote:
> On Tue, Nov 18, 2014 at 11:23:49AM +0800, Jason Wang wrote:
>> On 11/17/2014 06:11 PM, Michael S. Tsirkin wrote:
>>> On Mon, Nov 17, 2014 at 10:44:30AM +0100, Cornelia Huck wrote:
>>>> On Mon, 17 Nov 2014 11:37:01 +0200
>>>> "Michael S. Tsirkin" <mst@redhat.com> wrote:
>>>>
>>>>> On Mon, Nov 17, 2014 at 05:17:17PM +0800, Jason Wang wrote:
>>>>>> 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 sanitize_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@rustcorp.com.au>
>>>>>> Cc: Michael S. Tsirkin <mst@redhat.com>
>>>>>> Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
>>>>>> Cc: Wanlong Gao <gaowanlong@cn.fujitsu.com>
>>>>>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>>>>> Hmm this conflicts with virtio 1.0 work: we drop
>>>>> features as bitmap there.
>>>> But that's an implementation detail, no? We'll still need a way for the
>>>> driver to sanitize features, and I think this interface works just fine.
>>> Now that you mention it, I don't think we do.
>>>
>>> The spec is quite explicit that devices must not expose invalid
>>> combinations of features.
>>>
>>> Admittedly, BUG_ON isn't very friendly to hypervisors.
>>>
>>> But e.g. failing probe seems better than trying to work around
>>> hypervisor bugs - otherwise we'll be stuck maintaining compatibility
>>> with hypervisors forever.
>>>
>> I'm ok with failing the probe.
>>
>> But it won't cost big effort to workaround only features dependencies
>> issue.
> From experience, second-guessing user always adds maintainance.
>
>> I don't see how this block any further features implementation.
>> Looking at virtio-net, it also depends on network core to fix NETIF_F_*
>> dependencies.
> That code is common for all drivers, so it was moved to core.
>
>> There seems no way to get rid of maintaining compatibility, e.g  the
>> workarounds for the buggy hypervisor without VIRTIO_F_ANY_LAYOUT support.
> Right - because too many hypervisors shipped without it, it's too
> much work to fix them all.
> No such motivation here, right?
>

Right, will post the patch that just fail the probe of virtio-net.

Thanks