[1/2] virito: introduce methods of fixing device features
diff mbox series

Message ID 1415857974-23326-1-git-send-email-jasowang@redhat.com
State New, archived
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  • [1/2] virito: introduce methods of fixing device features
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Commit Message

Jason Wang Nov. 13, 2014, 5:52 a.m. UTC
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@rustcorp.com.au>
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 drivers/virtio/virtio.c       |  4 ++++
 include/linux/virtio.h        |  1 +
 include/linux/virtio_config.h | 12 ++++++++++++
 3 files changed, 17 insertions(+)

Comments

Cornelia Huck Nov. 13, 2014, 8:46 a.m. UTC | #1
On Thu, 13 Nov 2014 13:52:53 +0800
Jason Wang <jasowang@redhat.com> wrote:

typo in subject-prefix: s/virito/virtio/

> 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.

So the basic problem this patch fixes is that an individual driver may
only specify a static set of features but cannot specify any
dependencies, right? Adding a sanitizer step makes sense, I guess.

> 
> Virtio-net will be the first user.
> 
> Cc: Rusty Russell <rusty@rustcorp.com.au>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Jason Wang <jasowang@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);

I'd probably call this "sanitize_features" instead.

> +
>  	dev->config->finalize_features(dev);
> 
>  	err = drv->probe(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));

When we add virtio-1 support, we can add a check for FEATURES_OK here,
so we're really on the safe side.

> +
> +	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)

The approach looks good to me.

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Jason Wang Nov. 13, 2014, 9:11 a.m. UTC | #2
On 11/13/2014 04:46 PM, Cornelia Huck wrote:
> On Thu, 13 Nov 2014 13:52:53 +0800
> Jason Wang <jasowang@redhat.com> wrote:
>
> typo in subject-prefix: s/virito/virtio/
>

Will correct this.
>> 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.
> So the basic problem this patch fixes is that an individual driver may
> only specify a static set of features but cannot specify any
> dependencies, right?

Right, and what even worse is qemu could not handle dependencies as
well. So we need fix both sides.
>  Adding a sanitizer step makes sense, I guess.
>
>> Virtio-net will be the first user.
>>
>> Cc: Rusty Russell <rusty@rustcorp.com.au>
>> Cc: Michael S. Tsirkin <mst@redhat.com>
>> Signed-off-by: Jason Wang <jasowang@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);
> I'd probably call this "sanitize_features" instead.

Ok.
>> +
>>  	dev->config->finalize_features(dev);
>>
>>  	err = drv->probe(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));
> When we add virtio-1 support, we can add a check for FEATURES_OK here,
> so we're really on the safe side.
>

If I read the spec correctly, FEATURES_OK was set only after writing the
features bits to device. But we want to sanitize the them before.
>> +
>> +	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)
> The approach looks good to me.
>

Thanks for the review.
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Cornelia Huck Nov. 13, 2014, 9:14 a.m. UTC | #3
On Thu, 13 Nov 2014 17:11:30 +0800
Jason Wang <jasowang@redhat.com> wrote:

> On 11/13/2014 04:46 PM, Cornelia Huck wrote:
> > On Thu, 13 Nov 2014 13:52:53 +0800
> > Jason Wang <jasowang@redhat.com> wrote:

> >> +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));
> > When we add virtio-1 support, we can add a check for FEATURES_OK here,
> > so we're really on the safe side.
> >
> 
> If I read the spec correctly, FEATURES_OK was set only after writing the
> features bits to device. But we want to sanitize the them before.

I meant doing a BUG when FEATURES_OK is set - sorry for not being clear.

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Jason Wang Nov. 13, 2014, 9:49 a.m. UTC | #4
On 11/13/2014 05:14 PM, Cornelia Huck wrote:
> On Thu, 13 Nov 2014 17:11:30 +0800
> Jason Wang <jasowang@redhat.com> wrote:
>
>> On 11/13/2014 04:46 PM, Cornelia Huck wrote:
>>> On Thu, 13 Nov 2014 13:52:53 +0800
>>> Jason Wang <jasowang@redhat.com> wrote:
>>>> +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));
>>> When we add virtio-1 support, we can add a check for FEATURES_OK here,
>>> so we're really on the safe side.
>>>
>> If I read the spec correctly, FEATURES_OK was set only after writing the
>> features bits to device. But we want to sanitize the them before.
> I meant doing a BUG when FEATURES_OK is set - sorry for not being clear.
>

I get it, thanks for the clarification.
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Rusty Russell Nov. 24, 2014, 1:08 a.m. UTC | #5
Jason Wang <jasowang@redhat.com> writes:
> 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.

Sorry, I've been focussing elsewhere.

I would really prefer that drivers offer a "feature_depends" table,
which can indicate that feature A depends on feature B, and have the
core iterate, complain and fixup as necessary.

Is that expressive enough, or do we need more?

Thanks,
Rusty.
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Jason Wang Nov. 26, 2014, 7:09 a.m. UTC | #6
----- Original Message -----
> Jason Wang <jasowang@redhat.com> writes:
> > 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.
> 
> Sorry, I've been focussing elsewhere.
> 
> I would really prefer that drivers offer a "feature_depends" table,
> which can indicate that feature A depends on feature B, and have the
> core iterate, complain and fixup as necessary.
> 
> Is that expressive enough, or do we need more?
> 
> Thanks,
> Rusty.

I suggested something like this in https://lkml.org/lkml/2014/11/19/132, but
Michael does not like it ...
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Patch
diff mbox series

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)