RE: [PATCH V4 3/6] vDPA: allow userspace to query features of a vDPA device

RE: [PATCH V4 3/6] vDPA: allow userspace to query features of a vDPA device

[Parav Pandit via Virtualization]

> From: Zhu Lingshan <lingshan.zhu@intel.com>
> Sent: Friday, July 22, 2022 7:53 AM
> 
> This commit adds a new vDPA netlink attribution
> VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES. Userspace can query
> features of vDPA devices through this new attr.
> 
> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
> ---
>  drivers/vdpa/vdpa.c       | 13 +++++++++----
>  include/uapi/linux/vdpa.h |  1 +
>  2 files changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c index
> ebf2f363fbe7..9b0e39b2f022 100644
> --- a/drivers/vdpa/vdpa.c
> +++ b/drivers/vdpa/vdpa.c
> @@ -815,7 +815,7 @@ static int vdpa_dev_net_mq_config_fill(struct
> vdpa_device *vdev,  static int vdpa_dev_net_config_fill(struct vdpa_device
> *vdev, struct sk_buff *msg)  {
>  	struct virtio_net_config config = {};
> -	u64 features;
> +	u64 features_device, features_driver;
>  	u16 val_u16;
> 
>  	vdpa_get_config_unlocked(vdev, 0, &config, sizeof(config)); @@ -
> 832,12 +832,17 @@ static int vdpa_dev_net_config_fill(struct vdpa_device
> *vdev, struct sk_buff *ms
>  	if (nla_put_u16(msg, VDPA_ATTR_DEV_NET_CFG_MTU, val_u16))
>  		return -EMSGSIZE;
> 
> -	features = vdev->config->get_driver_features(vdev);
> -	if (nla_put_u64_64bit(msg,
> VDPA_ATTR_DEV_NEGOTIATED_FEATURES, features,
> +	features_driver = vdev->config->get_driver_features(vdev);
> +	if (nla_put_u64_64bit(msg,
> VDPA_ATTR_DEV_NEGOTIATED_FEATURES, features_driver,
> +			      VDPA_ATTR_PAD))
> +		return -EMSGSIZE;
> +
> +	features_device = vdev->config->get_device_features(vdev);
> +	if (nla_put_u64_64bit(msg,
> VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES,
> +features_device,
>  			      VDPA_ATTR_PAD))
>  		return -EMSGSIZE;
> 
> -	return vdpa_dev_net_mq_config_fill(vdev, msg, features, &config);
> +	return vdpa_dev_net_mq_config_fill(vdev, msg, features_driver,
> +&config);
>  }
> 
>  static int
> diff --git a/include/uapi/linux/vdpa.h b/include/uapi/linux/vdpa.h index
> 25c55cab3d7c..39f1c3d7c112 100644
> --- a/include/uapi/linux/vdpa.h
> +++ b/include/uapi/linux/vdpa.h
> @@ -47,6 +47,7 @@ enum vdpa_attr {
>  	VDPA_ATTR_DEV_NEGOTIATED_FEATURES,	/* u64 */
>  	VDPA_ATTR_DEV_MGMTDEV_MAX_VQS,		/* u32 */
>  	VDPA_ATTR_DEV_SUPPORTED_FEATURES,	/* u64 */
> +	VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES,	/* u64 */
> 
I have answered in previous emails.
I disagree with the change.
Please reuse VDPA_ATTR_DEV_SUPPORTED_FEATURES.

MST,
I nack this patch.
As mentioned in the previous versions, also it is missing the example output in the commit log.
Please include example output.

>  	VDPA_ATTR_DEV_QUEUE_INDEX,              /* u32 */
>  	VDPA_ATTR_DEV_VENDOR_ATTR_NAME,		/* string */
> --
> 2.31.1

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RE: [PATCH V4 5/6] vDPA: answer num of queue pairs = 1 to userspace when VIRTIO_NET_F_MQ == 0

[Parav Pandit via Virtualization]

> From: Zhu Lingshan <lingshan.zhu@intel.com>
> Sent: Friday, July 22, 2022 7:53 AM
> 
> If VIRTIO_NET_F_MQ == 0, the virtio device should have one queue pair, so
> when userspace querying queue pair numbers, it should return mq=1 than
> zero.
> 
> Function vdpa_dev_net_config_fill() fills the attributions of the vDPA
> devices, so that it should call vdpa_dev_net_mq_config_fill() so the
> parameter in vdpa_dev_net_mq_config_fill() should be feature_device than
> feature_driver for the vDPA devices themselves
> 
> Before this change, when MQ = 0, iproute2 output:
> $vdpa dev config show vdpa0
> vdpa0: mac 00:e8:ca:11:be:05 link up link_announce false max_vq_pairs 0
> mtu 1500
> 
> After applying this commit, when MQ = 0, iproute2 output:
> $vdpa dev config show vdpa0
> vdpa0: mac 00:e8:ca:11:be:05 link up link_announce false max_vq_pairs 1
> mtu 1500
> 
No. We do not want to diverge returning values of config space for fields which are not present as discussed in previous versions.
Please drop this patch.
Nack on this patch.

> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
> ---
>  drivers/vdpa/vdpa.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c index
> d76b22b2f7ae..846dd37f3549 100644
> --- a/drivers/vdpa/vdpa.c
> +++ b/drivers/vdpa/vdpa.c
> @@ -806,9 +806,10 @@ static int vdpa_dev_net_mq_config_fill(struct
> vdpa_device *vdev,
>  	u16 val_u16;
> 
>  	if ((features & BIT_ULL(VIRTIO_NET_F_MQ)) == 0)
> -		return 0;
> +		val_u16 = 1;
> +	else
> +		val_u16 = __virtio16_to_cpu(true, config-
> >max_virtqueue_pairs);
> 
> -	val_u16 = le16_to_cpu(config->max_virtqueue_pairs);
>  	return nla_put_u16(msg, VDPA_ATTR_DEV_NET_CFG_MAX_VQP,
> val_u16);  }
> 
> @@ -842,7 +843,7 @@ static int vdpa_dev_net_config_fill(struct
> vdpa_device *vdev, struct sk_buff *ms
>  			      VDPA_ATTR_PAD))
>  		return -EMSGSIZE;
> 
> -	return vdpa_dev_net_mq_config_fill(vdev, msg, features_driver,
> &config);
> +	return vdpa_dev_net_mq_config_fill(vdev, msg, features_device,
> +&config);
>  }
> 
>  static int
> --
> 2.31.1

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RE: [PATCH V4 3/6] vDPA: allow userspace to query features of a vDPA device

[Parav Pandit via Virtualization]

> From: Zhu, Lingshan <lingshan.zhu@intel.com>
> Sent: Saturday, July 23, 2022 7:24 AM
> 
> 
> On 7/22/2022 9:12 PM, Parav Pandit wrote:
> >> From: Zhu Lingshan <lingshan.zhu@intel.com>
> >> Sent: Friday, July 22, 2022 7:53 AM
> >>
> >> This commit adds a new vDPA netlink attribution
> >> VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES. Userspace can query
> features
> >> of vDPA devices through this new attr.
> >>
> >> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
> >> ---
> >>   drivers/vdpa/vdpa.c       | 13 +++++++++----
> >>   include/uapi/linux/vdpa.h |  1 +
> >>   2 files changed, 10 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c index
> >> ebf2f363fbe7..9b0e39b2f022 100644
> >> --- a/drivers/vdpa/vdpa.c
> >> +++ b/drivers/vdpa/vdpa.c
> >> @@ -815,7 +815,7 @@ static int vdpa_dev_net_mq_config_fill(struct
> >> vdpa_device *vdev,  static int vdpa_dev_net_config_fill(struct
> >> vdpa_device *vdev, struct sk_buff *msg)  {
> >>   	struct virtio_net_config config = {};
> >> -	u64 features;
> >> +	u64 features_device, features_driver;
> >>   	u16 val_u16;
> >>
> >>   	vdpa_get_config_unlocked(vdev, 0, &config, sizeof(config)); @@ -
> >> 832,12 +832,17 @@ static int vdpa_dev_net_config_fill(struct
> >> vdpa_device *vdev, struct sk_buff *ms
> >>   	if (nla_put_u16(msg, VDPA_ATTR_DEV_NET_CFG_MTU, val_u16))
> >>   		return -EMSGSIZE;
> >>
> >> -	features = vdev->config->get_driver_features(vdev);
> >> -	if (nla_put_u64_64bit(msg,
> >> VDPA_ATTR_DEV_NEGOTIATED_FEATURES, features,
> >> +	features_driver = vdev->config->get_driver_features(vdev);
> >> +	if (nla_put_u64_64bit(msg,
> >> VDPA_ATTR_DEV_NEGOTIATED_FEATURES, features_driver,
> >> +			      VDPA_ATTR_PAD))
> >> +		return -EMSGSIZE;
> >> +
> >> +	features_device = vdev->config->get_device_features(vdev);
> >> +	if (nla_put_u64_64bit(msg,
> >> VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES,
> >> +features_device,
> >>   			      VDPA_ATTR_PAD))
> >>   		return -EMSGSIZE;
> >>
> >> -	return vdpa_dev_net_mq_config_fill(vdev, msg, features, &config);
> >> +	return vdpa_dev_net_mq_config_fill(vdev, msg, features_driver,
> >> +&config);
> >>   }
> >>
> >>   static int
> >> diff --git a/include/uapi/linux/vdpa.h b/include/uapi/linux/vdpa.h
> >> index
> >> 25c55cab3d7c..39f1c3d7c112 100644
> >> --- a/include/uapi/linux/vdpa.h
> >> +++ b/include/uapi/linux/vdpa.h
> >> @@ -47,6 +47,7 @@ enum vdpa_attr {
> >>   	VDPA_ATTR_DEV_NEGOTIATED_FEATURES,	/* u64 */
> >>   	VDPA_ATTR_DEV_MGMTDEV_MAX_VQS,		/* u32 */
> >>   	VDPA_ATTR_DEV_SUPPORTED_FEATURES,	/* u64 */
> >> +	VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES,	/* u64 */
> >>
> > I have answered in previous emails.
> > I disagree with the change.
> > Please reuse VDPA_ATTR_DEV_SUPPORTED_FEATURES.
> I believe we have already discussed this before in the V3 thread.
> I have told you that reusing this attr will lead to a new race condition.
>
Returning attribute cannot lead to any race condition.

 
> Pleas refer to the previous thread, and you did not answer my questions in
> that thread.
> 
> Thanks,
> Zhu Lingshan
> >
> > MST,
> > I nack this patch.
> > As mentioned in the previous versions, also it is missing the example
> output in the commit log.
> > Please include example output.
> >
> >>   	VDPA_ATTR_DEV_QUEUE_INDEX,              /* u32 */
> >>   	VDPA_ATTR_DEV_VENDOR_ATTR_NAME,		/* string */
> >> --
> >> 2.31.1

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RE: [PATCH V4 3/6] vDPA: allow userspace to query features of a vDPA device

[Parav Pandit via Virtualization]

> From: Zhu, Lingshan <lingshan.zhu@intel.com>
> Sent: Tuesday, July 26, 2022 7:03 AM
> 
> On 7/24/2022 11:21 PM, Parav Pandit wrote:
> >
> >> From: Zhu, Lingshan <lingshan.zhu@intel.com>
> >> Sent: Saturday, July 23, 2022 7:24 AM
> >>
> >>
> >> On 7/22/2022 9:12 PM, Parav Pandit wrote:
> >>>> From: Zhu Lingshan <lingshan.zhu@intel.com>
> >>>> Sent: Friday, July 22, 2022 7:53 AM
> >>>>
> >>>> This commit adds a new vDPA netlink attribution
> >>>> VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES. Userspace can
> query
> >> features
> >>>> of vDPA devices through this new attr.
> >>>>
> >>>> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
> >>>> ---
> >>>>    drivers/vdpa/vdpa.c       | 13 +++++++++----
> >>>>    include/uapi/linux/vdpa.h |  1 +
> >>>>    2 files changed, 10 insertions(+), 4 deletions(-)
> >>>>
> >>>> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c index
> >>>> ebf2f363fbe7..9b0e39b2f022 100644
> >>>> --- a/drivers/vdpa/vdpa.c
> >>>> +++ b/drivers/vdpa/vdpa.c
> >>>> @@ -815,7 +815,7 @@ static int vdpa_dev_net_mq_config_fill(struct
> >>>> vdpa_device *vdev,  static int vdpa_dev_net_config_fill(struct
> >>>> vdpa_device *vdev, struct sk_buff *msg)  {
> >>>>    	struct virtio_net_config config = {};
> >>>> -	u64 features;
> >>>> +	u64 features_device, features_driver;
> >>>>    	u16 val_u16;
> >>>>
> >>>>    	vdpa_get_config_unlocked(vdev, 0, &config, sizeof(config)); @@
> >>>> -
> >>>> 832,12 +832,17 @@ static int vdpa_dev_net_config_fill(struct
> >>>> vdpa_device *vdev, struct sk_buff *ms
> >>>>    	if (nla_put_u16(msg, VDPA_ATTR_DEV_NET_CFG_MTU, val_u16))
> >>>>    		return -EMSGSIZE;
> >>>>
> >>>> -	features = vdev->config->get_driver_features(vdev);
> >>>> -	if (nla_put_u64_64bit(msg,
> >>>> VDPA_ATTR_DEV_NEGOTIATED_FEATURES, features,
> >>>> +	features_driver = vdev->config->get_driver_features(vdev);
> >>>> +	if (nla_put_u64_64bit(msg,
> >>>> VDPA_ATTR_DEV_NEGOTIATED_FEATURES, features_driver,
> >>>> +			      VDPA_ATTR_PAD))
> >>>> +		return -EMSGSIZE;
> >>>> +
> >>>> +	features_device = vdev->config->get_device_features(vdev);
> >>>> +	if (nla_put_u64_64bit(msg,
> >>>> VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES,
> >>>> +features_device,
> >>>>    			      VDPA_ATTR_PAD))
> >>>>    		return -EMSGSIZE;
> >>>>
> >>>> -	return vdpa_dev_net_mq_config_fill(vdev, msg, features, &config);
> >>>> +	return vdpa_dev_net_mq_config_fill(vdev, msg, features_driver,
> >>>> +&config);
> >>>>    }
> >>>>
> >>>>    static int
> >>>> diff --git a/include/uapi/linux/vdpa.h b/include/uapi/linux/vdpa.h
> >>>> index
> >>>> 25c55cab3d7c..39f1c3d7c112 100644
> >>>> --- a/include/uapi/linux/vdpa.h
> >>>> +++ b/include/uapi/linux/vdpa.h
> >>>> @@ -47,6 +47,7 @@ enum vdpa_attr {
> >>>>    	VDPA_ATTR_DEV_NEGOTIATED_FEATURES,	/* u64 */
> >>>>    	VDPA_ATTR_DEV_MGMTDEV_MAX_VQS,		/* u32 */
> >>>>    	VDPA_ATTR_DEV_SUPPORTED_FEATURES,	/* u64 */
> >>>> +	VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES,	/* u64 */
> >>>>
> >>> I have answered in previous emails.
> >>> I disagree with the change.
> >>> Please reuse VDPA_ATTR_DEV_SUPPORTED_FEATURES.
> >> I believe we have already discussed this before in the V3 thread.
> >> I have told you that reusing this attr will lead to a new race condition.
> >>
> > Returning attribute cannot lead to any race condition.
> Please refer to our discussion in the V3 series, I have explained if re-use this
> attr, it will be a multiple consumers and multiple produces model, it is a
> typical racing condition.

I read the emails with subject = " Re: [PATCH V3 3/6] vDPA: allow userspace to query features of a vDPA device"
I couldn’t find multiple consumers multiple producers working on same nla message.
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Re: [PATCH V4 3/6] vDPA: allow userspace to query features of a vDPA device

[Zhu Lingshan]

On 7/26/2022 7:06 PM, Parav Pandit via Virtualization wrote:
>> From: Zhu, Lingshan <lingshan.zhu@intel.com>
>> Sent: Tuesday, July 26, 2022 7:03 AM
>>
>> On 7/24/2022 11:21 PM, Parav Pandit wrote:
>>>> From: Zhu, Lingshan <lingshan.zhu@intel.com>
>>>> Sent: Saturday, July 23, 2022 7:24 AM
>>>>
>>>>
>>>> On 7/22/2022 9:12 PM, Parav Pandit wrote:
>>>>>> From: Zhu Lingshan <lingshan.zhu@intel.com>
>>>>>> Sent: Friday, July 22, 2022 7:53 AM
>>>>>>
>>>>>> This commit adds a new vDPA netlink attribution
>>>>>> VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES. Userspace can
>> query
>>>> features
>>>>>> of vDPA devices through this new attr.
>>>>>>
>>>>>> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
>>>>>> ---
>>>>>>     drivers/vdpa/vdpa.c       | 13 +++++++++----
>>>>>>     include/uapi/linux/vdpa.h |  1 +
>>>>>>     2 files changed, 10 insertions(+), 4 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c index
>>>>>> ebf2f363fbe7..9b0e39b2f022 100644
>>>>>> --- a/drivers/vdpa/vdpa.c
>>>>>> +++ b/drivers/vdpa/vdpa.c
>>>>>> @@ -815,7 +815,7 @@ static int vdpa_dev_net_mq_config_fill(struct
>>>>>> vdpa_device *vdev,  static int vdpa_dev_net_config_fill(struct
>>>>>> vdpa_device *vdev, struct sk_buff *msg)  {
>>>>>>     	struct virtio_net_config config = {};
>>>>>> -	u64 features;
>>>>>> +	u64 features_device, features_driver;
>>>>>>     	u16 val_u16;
>>>>>>
>>>>>>     	vdpa_get_config_unlocked(vdev, 0, &config, sizeof(config)); @@
>>>>>> -
>>>>>> 832,12 +832,17 @@ static int vdpa_dev_net_config_fill(struct
>>>>>> vdpa_device *vdev, struct sk_buff *ms
>>>>>>     	if (nla_put_u16(msg, VDPA_ATTR_DEV_NET_CFG_MTU, val_u16))
>>>>>>     		return -EMSGSIZE;
>>>>>>
>>>>>> -	features = vdev->config->get_driver_features(vdev);
>>>>>> -	if (nla_put_u64_64bit(msg,
>>>>>> VDPA_ATTR_DEV_NEGOTIATED_FEATURES, features,
>>>>>> +	features_driver = vdev->config->get_driver_features(vdev);
>>>>>> +	if (nla_put_u64_64bit(msg,
>>>>>> VDPA_ATTR_DEV_NEGOTIATED_FEATURES, features_driver,
>>>>>> +			      VDPA_ATTR_PAD))
>>>>>> +		return -EMSGSIZE;
>>>>>> +
>>>>>> +	features_device = vdev->config->get_device_features(vdev);
>>>>>> +	if (nla_put_u64_64bit(msg,
>>>>>> VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES,
>>>>>> +features_device,
>>>>>>     			      VDPA_ATTR_PAD))
>>>>>>     		return -EMSGSIZE;
>>>>>>
>>>>>> -	return vdpa_dev_net_mq_config_fill(vdev, msg, features, &config);
>>>>>> +	return vdpa_dev_net_mq_config_fill(vdev, msg, features_driver,
>>>>>> +&config);
>>>>>>     }
>>>>>>
>>>>>>     static int
>>>>>> diff --git a/include/uapi/linux/vdpa.h b/include/uapi/linux/vdpa.h
>>>>>> index
>>>>>> 25c55cab3d7c..39f1c3d7c112 100644
>>>>>> --- a/include/uapi/linux/vdpa.h
>>>>>> +++ b/include/uapi/linux/vdpa.h
>>>>>> @@ -47,6 +47,7 @@ enum vdpa_attr {
>>>>>>     	VDPA_ATTR_DEV_NEGOTIATED_FEATURES,	/* u64 */
>>>>>>     	VDPA_ATTR_DEV_MGMTDEV_MAX_VQS,		/* u32 */
>>>>>>     	VDPA_ATTR_DEV_SUPPORTED_FEATURES,	/* u64 */
>>>>>> +	VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES,	/* u64 */
>>>>>>
>>>>> I have answered in previous emails.
>>>>> I disagree with the change.
>>>>> Please reuse VDPA_ATTR_DEV_SUPPORTED_FEATURES.
>>>> I believe we have already discussed this before in the V3 thread.
>>>> I have told you that reusing this attr will lead to a new race condition.
>>>>
>>> Returning attribute cannot lead to any race condition.
>> Please refer to our discussion in the V3 series, I have explained if re-use this
>> attr, it will be a multiple consumers and multiple produces model, it is a
>> typical racing condition.
> I read the emails with subject = " Re: [PATCH V3 3/6] vDPA: allow userspace to query features of a vDPA device"
> I couldn’t find multiple consumers multiple producers working on same nla message.
what if two or more iproute2 instance or other userspace tools querying 
the features of the management device and the vDPA device
simultaneously? In such a case, there are multiple consumers in the 
userspace, and the kernel functions(to fill management device
features and vDPA device features) are the multiple producers. And there 
are no locks.

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Re: [PATCH V4 3/6] vDPA: allow userspace to query features of a vDPA device

[Michael S. Tsirkin]

On Fri, Jul 22, 2022 at 07:53:06PM +0800, Zhu Lingshan wrote:
> This commit adds a new vDPA netlink attribution
> VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES. Userspace can query
> features of vDPA devices through this new attr.
> 
> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>


I think at least some discussion and documentation
of this attribute versus VDPA_ATTR_DEV_SUPPORTED_FEATURES
is called for.

Otherwise how do people know which one to use?

We can't send everyone to go read the lkml thread.

> ---
>  drivers/vdpa/vdpa.c       | 13 +++++++++----
>  include/uapi/linux/vdpa.h |  1 +
>  2 files changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
> index ebf2f363fbe7..9b0e39b2f022 100644
> --- a/drivers/vdpa/vdpa.c
> +++ b/drivers/vdpa/vdpa.c
> @@ -815,7 +815,7 @@ static int vdpa_dev_net_mq_config_fill(struct vdpa_device *vdev,
>  static int vdpa_dev_net_config_fill(struct vdpa_device *vdev, struct sk_buff *msg)
>  {
>  	struct virtio_net_config config = {};
> -	u64 features;
> +	u64 features_device, features_driver;
>  	u16 val_u16;
>  
>  	vdpa_get_config_unlocked(vdev, 0, &config, sizeof(config));
> @@ -832,12 +832,17 @@ static int vdpa_dev_net_config_fill(struct vdpa_device *vdev, struct sk_buff *ms
>  	if (nla_put_u16(msg, VDPA_ATTR_DEV_NET_CFG_MTU, val_u16))
>  		return -EMSGSIZE;
>  
> -	features = vdev->config->get_driver_features(vdev);
> -	if (nla_put_u64_64bit(msg, VDPA_ATTR_DEV_NEGOTIATED_FEATURES, features,
> +	features_driver = vdev->config->get_driver_features(vdev);
> +	if (nla_put_u64_64bit(msg, VDPA_ATTR_DEV_NEGOTIATED_FEATURES, features_driver,
> +			      VDPA_ATTR_PAD))
> +		return -EMSGSIZE;
> +
> +	features_device = vdev->config->get_device_features(vdev);
> +	if (nla_put_u64_64bit(msg, VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES, features_device,
>  			      VDPA_ATTR_PAD))
>  		return -EMSGSIZE;
>  
> -	return vdpa_dev_net_mq_config_fill(vdev, msg, features, &config);
> +	return vdpa_dev_net_mq_config_fill(vdev, msg, features_driver, &config);
>  }
>  
>  static int
> diff --git a/include/uapi/linux/vdpa.h b/include/uapi/linux/vdpa.h
> index 25c55cab3d7c..39f1c3d7c112 100644
> --- a/include/uapi/linux/vdpa.h
> +++ b/include/uapi/linux/vdpa.h
> @@ -47,6 +47,7 @@ enum vdpa_attr {
>  	VDPA_ATTR_DEV_NEGOTIATED_FEATURES,	/* u64 */
>  	VDPA_ATTR_DEV_MGMTDEV_MAX_VQS,		/* u32 */
>  	VDPA_ATTR_DEV_SUPPORTED_FEATURES,	/* u64 */
> +	VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES,	/* u64 */
>  
>  	VDPA_ATTR_DEV_QUEUE_INDEX,              /* u32 */
>  	VDPA_ATTR_DEV_VENDOR_ATTR_NAME,		/* string */
> -- 
> 2.31.1

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RE: [PATCH V4 3/6] vDPA: allow userspace to query features of a vDPA device

[Parav Pandit via Virtualization]

> From: Zhu, Lingshan <lingshan.zhu@intel.com>
> Sent: Wednesday, July 27, 2022 2:02 AM
> 
> 
> On 7/26/2022 7:06 PM, Parav Pandit wrote:
> >> From: Zhu, Lingshan <lingshan.zhu@intel.com>
> >> Sent: Tuesday, July 26, 2022 7:03 AM
> >>
> >> On 7/24/2022 11:21 PM, Parav Pandit wrote:
> >>>> From: Zhu, Lingshan <lingshan.zhu@intel.com>
> >>>> Sent: Saturday, July 23, 2022 7:24 AM
> >>>>
> >>>>
> >>>> On 7/22/2022 9:12 PM, Parav Pandit wrote:
> >>>>>> From: Zhu Lingshan <lingshan.zhu@intel.com>
> >>>>>> Sent: Friday, July 22, 2022 7:53 AM
> >>>>>>
> >>>>>> This commit adds a new vDPA netlink attribution
> >>>>>> VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES. Userspace can
> >> query
> >>>> features
> >>>>>> of vDPA devices through this new attr.
> >>>>>>
> >>>>>> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
> >>>>>> ---
> >>>>>>     drivers/vdpa/vdpa.c       | 13 +++++++++----
> >>>>>>     include/uapi/linux/vdpa.h |  1 +
> >>>>>>     2 files changed, 10 insertions(+), 4 deletions(-)
> >>>>>>
> >>>>>> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c index
> >>>>>> ebf2f363fbe7..9b0e39b2f022 100644
> >>>>>> --- a/drivers/vdpa/vdpa.c
> >>>>>> +++ b/drivers/vdpa/vdpa.c
> >>>>>> @@ -815,7 +815,7 @@ static int
> vdpa_dev_net_mq_config_fill(struct
> >>>>>> vdpa_device *vdev,  static int vdpa_dev_net_config_fill(struct
> >>>>>> vdpa_device *vdev, struct sk_buff *msg)  {
> >>>>>>     	struct virtio_net_config config = {};
> >>>>>> -	u64 features;
> >>>>>> +	u64 features_device, features_driver;
> >>>>>>     	u16 val_u16;
> >>>>>>
> >>>>>>     	vdpa_get_config_unlocked(vdev, 0, &config, sizeof(config));
> >>>>>> @@
> >>>>>> -
> >>>>>> 832,12 +832,17 @@ static int vdpa_dev_net_config_fill(struct
> >>>>>> vdpa_device *vdev, struct sk_buff *ms
> >>>>>>     	if (nla_put_u16(msg, VDPA_ATTR_DEV_NET_CFG_MTU,
> val_u16))
> >>>>>>     		return -EMSGSIZE;
> >>>>>>
> >>>>>> -	features = vdev->config->get_driver_features(vdev);
> >>>>>> -	if (nla_put_u64_64bit(msg,
> >>>>>> VDPA_ATTR_DEV_NEGOTIATED_FEATURES, features,
> >>>>>> +	features_driver = vdev->config->get_driver_features(vdev);
> >>>>>> +	if (nla_put_u64_64bit(msg,
> >>>>>> VDPA_ATTR_DEV_NEGOTIATED_FEATURES, features_driver,
> >>>>>> +			      VDPA_ATTR_PAD))
> >>>>>> +		return -EMSGSIZE;
> >>>>>> +
> >>>>>> +	features_device = vdev->config->get_device_features(vdev);
> >>>>>> +	if (nla_put_u64_64bit(msg,
> >>>>>> VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES,
> >>>>>> +features_device,
> >>>>>>     			      VDPA_ATTR_PAD))
> >>>>>>     		return -EMSGSIZE;
> >>>>>>
> >>>>>> -	return vdpa_dev_net_mq_config_fill(vdev, msg, features,
> &config);
> >>>>>> +	return vdpa_dev_net_mq_config_fill(vdev, msg,
> features_driver,
> >>>>>> +&config);
> >>>>>>     }
> >>>>>>
> >>>>>>     static int
> >>>>>> diff --git a/include/uapi/linux/vdpa.h
> >>>>>> b/include/uapi/linux/vdpa.h index
> >>>>>> 25c55cab3d7c..39f1c3d7c112 100644
> >>>>>> --- a/include/uapi/linux/vdpa.h
> >>>>>> +++ b/include/uapi/linux/vdpa.h
> >>>>>> @@ -47,6 +47,7 @@ enum vdpa_attr {
> >>>>>>     	VDPA_ATTR_DEV_NEGOTIATED_FEATURES,	/* u64 */
> >>>>>>     	VDPA_ATTR_DEV_MGMTDEV_MAX_VQS,		/*
> u32 */
> >>>>>>     	VDPA_ATTR_DEV_SUPPORTED_FEATURES,	/* u64 */
> >>>>>> +	VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES,	/*
> u64 */
> >>>>>>
> >>>>> I have answered in previous emails.
> >>>>> I disagree with the change.
> >>>>> Please reuse VDPA_ATTR_DEV_SUPPORTED_FEATURES.
> >>>> I believe we have already discussed this before in the V3 thread.
> >>>> I have told you that reusing this attr will lead to a new race condition.
> >>>>
> >>> Returning attribute cannot lead to any race condition.
> >> Please refer to our discussion in the V3 series, I have explained if
> >> re-use this attr, it will be a multiple consumers and multiple
> >> produces model, it is a typical racing condition.
> > I read the emails with subject = " Re: [PATCH V3 3/6] vDPA: allow userspace
> to query features of a vDPA device"
> > I couldn’t find multiple consumers multiple producers working on same nla
> message.
> If this attr is reused, then there can be multiple iproute2 instances or other
> applications querying feature bits of the management device and the vDPA
> device simultaneously, and both kernel side management feature bits filler

> function and vDPA device feature bits filler function can write the NLA
> message at the same time. That's the multiple consumers and producers,
> and no locks
No. Each filling up happens in each process context. There is no race here.
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RE: [PATCH V4 3/6] vDPA: allow userspace to query features of a vDPA device

[Parav Pandit via Virtualization]

> From: Michael S. Tsirkin <mst@redhat.com>
> Sent: Tuesday, August 9, 2022 3:24 PM
> 
> On Fri, Jul 22, 2022 at 07:53:06PM +0800, Zhu Lingshan wrote:
> > This commit adds a new vDPA netlink attribution
> > VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES. Userspace can query
> features of
> > vDPA devices through this new attr.
> >
> > Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
> 
> 
> I think at least some discussion and documentation of this attribute versus
> VDPA_ATTR_DEV_SUPPORTED_FEATURES is called for.
> 
> Otherwise how do people know which one to use?
> 
> We can't send everyone to go read the lkml thread.

There is no race here. Commit log is missing example anyway.
I explained multiple times that this patch and/or its previous version cannot proceed in same state.
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Re: [PATCH V4 5/6] vDPA: answer num of queue pairs = 1 to userspace when VIRTIO_NET_F_MQ == 0

[Michael S. Tsirkin]

On Fri, Jul 22, 2022 at 01:14:42PM +0000, Parav Pandit wrote:
> 
> 
> > From: Zhu Lingshan <lingshan.zhu@intel.com>
> > Sent: Friday, July 22, 2022 7:53 AM
> > 
> > If VIRTIO_NET_F_MQ == 0, the virtio device should have one queue pair, so
> > when userspace querying queue pair numbers, it should return mq=1 than
> > zero.
> > 
> > Function vdpa_dev_net_config_fill() fills the attributions of the vDPA
> > devices, so that it should call vdpa_dev_net_mq_config_fill() so the
> > parameter in vdpa_dev_net_mq_config_fill() should be feature_device than
> > feature_driver for the vDPA devices themselves
> > 
> > Before this change, when MQ = 0, iproute2 output:
> > $vdpa dev config show vdpa0
> > vdpa0: mac 00:e8:ca:11:be:05 link up link_announce false max_vq_pairs 0
> > mtu 1500
> > 
> > After applying this commit, when MQ = 0, iproute2 output:
> > $vdpa dev config show vdpa0
> > vdpa0: mac 00:e8:ca:11:be:05 link up link_announce false max_vq_pairs 1
> > mtu 1500
> > 
> No. We do not want to diverge returning values of config space for fields which are not present as discussed in previous versions.
> Please drop this patch.
> Nack on this patch.

Wrt this patch as far as I'm concerned you guys are bikeshedding.

Parav generally don't send nacks please they are not helpful.

Zhu Lingshan please always address comments in some way.  E.g. refer to
them in the commit log explaining the motivation and the alternatives.
I know you don't agree with Parav but ghosting isn't nice.

I still feel what we should have done is
not return a value, as long as we do return it we might
as well return something reasonable, not 0.

And I like it that this fixes sparse warning actually:
max_virtqueue_pairs it tagged as __virtio, not __le.

However, I am worried there is another bug here:
this is checking driver features. But really max vqs
should not depend on that, it depends on device
features, no?



> > Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
> > ---
> >  drivers/vdpa/vdpa.c | 7 ++++---
> >  1 file changed, 4 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c index
> > d76b22b2f7ae..846dd37f3549 100644
> > --- a/drivers/vdpa/vdpa.c
> > +++ b/drivers/vdpa/vdpa.c
> > @@ -806,9 +806,10 @@ static int vdpa_dev_net_mq_config_fill(struct
> > vdpa_device *vdev,
> >  	u16 val_u16;
> > 
> >  	if ((features & BIT_ULL(VIRTIO_NET_F_MQ)) == 0)
> > -		return 0;
> > +		val_u16 = 1;
> > +	else
> > +		val_u16 = __virtio16_to_cpu(true, config-
> > >max_virtqueue_pairs);
> > 
> > -	val_u16 = le16_to_cpu(config->max_virtqueue_pairs);
> >  	return nla_put_u16(msg, VDPA_ATTR_DEV_NET_CFG_MAX_VQP,
> > val_u16);  }
> > 
> > @@ -842,7 +843,7 @@ static int vdpa_dev_net_config_fill(struct
> > vdpa_device *vdev, struct sk_buff *ms
> >  			      VDPA_ATTR_PAD))
> >  		return -EMSGSIZE;
> > 
> > -	return vdpa_dev_net_mq_config_fill(vdev, msg, features_driver,
> > &config);
> > +	return vdpa_dev_net_mq_config_fill(vdev, msg, features_device,
> > +&config);
> >  }
> > 
> >  static int
> > --
> > 2.31.1

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RE: [PATCH V4 5/6] vDPA: answer num of queue pairs = 1 to userspace when VIRTIO_NET_F_MQ == 0

[Parav Pandit via Virtualization]

> From: Michael S. Tsirkin <mst@redhat.com>
> Sent: Tuesday, August 9, 2022 3:36 PM

> > > After applying this commit, when MQ = 0, iproute2 output:
> > > $vdpa dev config show vdpa0
> > > vdpa0: mac 00:e8:ca:11:be:05 link up link_announce false
> > > max_vq_pairs 1 mtu 1500
> > >
> > No. We do not want to diverge returning values of config space for fields
> which are not present as discussed in previous versions.
> > Please drop this patch.
> > Nack on this patch.
> 
> Wrt this patch as far as I'm concerned you guys are bikeshedding.
> 
> Parav generally don't send nacks please they are not helpful.

Ok. I explained the technical reasoning that we don't diverge in fields. All are linked to the respective feature bits uniformly.
This I explained repeatedly in almost v1 to v3.
And reporting 1 is mis-leading, because it says _MQ is not negotiated, how come this device tells its config space has max_qp = 1.

But if you want to proceed to diverge kernel on feature bits go ahead. It requires inspection feature but feature.
I just don't see how this can be well maintained.

Commit log doesn't even describe the weird use case that says "as user space, I do not want to read device feature bits and just want to read config space to decide...".
Odd..

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Re: [PATCH V4 5/6] vDPA: answer num of queue pairs = 1 to userspace when VIRTIO_NET_F_MQ == 0

[Si-Wei Liu]

On 8/9/2022 12:36 PM, Michael S. Tsirkin wrote:
> On Fri, Jul 22, 2022 at 01:14:42PM +0000, Parav Pandit wrote:
>>
>>> From: Zhu Lingshan <lingshan.zhu@intel.com>
>>> Sent: Friday, July 22, 2022 7:53 AM
>>>
>>> If VIRTIO_NET_F_MQ == 0, the virtio device should have one queue pair, so
>>> when userspace querying queue pair numbers, it should return mq=1 than
>>> zero.
>>>
>>> Function vdpa_dev_net_config_fill() fills the attributions of the vDPA
>>> devices, so that it should call vdpa_dev_net_mq_config_fill() so the
>>> parameter in vdpa_dev_net_mq_config_fill() should be feature_device than
>>> feature_driver for the vDPA devices themselves
>>>
>>> Before this change, when MQ = 0, iproute2 output:
>>> $vdpa dev config show vdpa0
>>> vdpa0: mac 00:e8:ca:11:be:05 link up link_announce false max_vq_pairs 0
>>> mtu 1500
>>>
>>> After applying this commit, when MQ = 0, iproute2 output:
>>> $vdpa dev config show vdpa0
>>> vdpa0: mac 00:e8:ca:11:be:05 link up link_announce false max_vq_pairs 1
>>> mtu 1500
>>>
>> No. We do not want to diverge returning values of config space for fields which are not present as discussed in previous versions.
>> Please drop this patch.
>> Nack on this patch.
> Wrt this patch as far as I'm concerned you guys are bikeshedding.
>
> Parav generally don't send nacks please they are not helpful.
>
> Zhu Lingshan please always address comments in some way.  E.g. refer to
> them in the commit log explaining the motivation and the alternatives.
> I know you don't agree with Parav but ghosting isn't nice.
>
> I still feel what we should have done is
> not return a value, as long as we do return it we might
> as well return something reasonable, not 0.
Maybe I missed something but I don't get this, when VIRTIO_NET_F_MQ is 
not negotiated, the VDPA_ATTR_DEV_NET_CFG_MAX_VQP attribute is simply 
not there, but userspace (iproute) mistakenly puts a zero value there. 
This is a pattern every tool in iproute follows consistently by large. I 
don't get why kernel has to return something without seeing a very 
convincing use case?

Not to mention spec doesn't give us explicit definition for when the 
field in config space becomes valid and/or the default value at first 
sights as part of feature negotiation. If we want to stick to the model 
Lingshan proposed, maybe fix the spec first then get back on the details?

-Siwei

>
> And I like it that this fixes sparse warning actually:
> max_virtqueue_pairs it tagged as __virtio, not __le.
>
> However, I am worried there is another bug here:
> this is checking driver features. But really max vqs
> should not depend on that, it depends on device
> features, no?
>
>
>
>>> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
>>> ---
>>>   drivers/vdpa/vdpa.c | 7 ++++---
>>>   1 file changed, 4 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c index
>>> d76b22b2f7ae..846dd37f3549 100644
>>> --- a/drivers/vdpa/vdpa.c
>>> +++ b/drivers/vdpa/vdpa.c
>>> @@ -806,9 +806,10 @@ static int vdpa_dev_net_mq_config_fill(struct
>>> vdpa_device *vdev,
>>>   	u16 val_u16;
>>>
>>>   	if ((features & BIT_ULL(VIRTIO_NET_F_MQ)) == 0)
>>> -		return 0;
>>> +		val_u16 = 1;
>>> +	else
>>> +		val_u16 = __virtio16_to_cpu(true, config-
>>>> max_virtqueue_pairs);
>>> -	val_u16 = le16_to_cpu(config->max_virtqueue_pairs);
>>>   	return nla_put_u16(msg, VDPA_ATTR_DEV_NET_CFG_MAX_VQP,
>>> val_u16);  }
>>>
>>> @@ -842,7 +843,7 @@ static int vdpa_dev_net_config_fill(struct
>>> vdpa_device *vdev, struct sk_buff *ms
>>>   			      VDPA_ATTR_PAD))
>>>   		return -EMSGSIZE;
>>>
>>> -	return vdpa_dev_net_mq_config_fill(vdev, msg, features_driver,
>>> &config);
>>> +	return vdpa_dev_net_mq_config_fill(vdev, msg, features_device,
>>> +&config);
>>>   }
>>>
>>>   static int
>>> --
>>> 2.31.1
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Re: [PATCH V4 5/6] vDPA: answer num of queue pairs = 1 to userspace when VIRTIO_NET_F_MQ == 0

[Jason Wang]

On Wed, Aug 10, 2022 at 8:54 AM Si-Wei Liu <si-wei.liu@oracle.com> wrote:
>
>
>
> On 8/9/2022 12:36 PM, Michael S. Tsirkin wrote:
> > On Fri, Jul 22, 2022 at 01:14:42PM +0000, Parav Pandit wrote:
> >>
> >>> From: Zhu Lingshan <lingshan.zhu@intel.com>
> >>> Sent: Friday, July 22, 2022 7:53 AM
> >>>
> >>> If VIRTIO_NET_F_MQ == 0, the virtio device should have one queue pair, so
> >>> when userspace querying queue pair numbers, it should return mq=1 than
> >>> zero.
> >>>
> >>> Function vdpa_dev_net_config_fill() fills the attributions of the vDPA
> >>> devices, so that it should call vdpa_dev_net_mq_config_fill() so the
> >>> parameter in vdpa_dev_net_mq_config_fill() should be feature_device than
> >>> feature_driver for the vDPA devices themselves
> >>>
> >>> Before this change, when MQ = 0, iproute2 output:
> >>> $vdpa dev config show vdpa0
> >>> vdpa0: mac 00:e8:ca:11:be:05 link up link_announce false max_vq_pairs 0
> >>> mtu 1500
> >>>
> >>> After applying this commit, when MQ = 0, iproute2 output:
> >>> $vdpa dev config show vdpa0
> >>> vdpa0: mac 00:e8:ca:11:be:05 link up link_announce false max_vq_pairs 1
> >>> mtu 1500
> >>>
> >> No. We do not want to diverge returning values of config space for fields which are not present as discussed in previous versions.
> >> Please drop this patch.
> >> Nack on this patch.
> > Wrt this patch as far as I'm concerned you guys are bikeshedding.
> >
> > Parav generally don't send nacks please they are not helpful.
> >
> > Zhu Lingshan please always address comments in some way.  E.g. refer to
> > them in the commit log explaining the motivation and the alternatives.
> > I know you don't agree with Parav but ghosting isn't nice.
> >
> > I still feel what we should have done is
> > not return a value, as long as we do return it we might
> > as well return something reasonable, not 0.
> Maybe I missed something but I don't get this, when VIRTIO_NET_F_MQ is
> not negotiated, the VDPA_ATTR_DEV_NET_CFG_MAX_VQP attribute is simply
> not there, but userspace (iproute) mistakenly puts a zero value there.
> This is a pattern every tool in iproute follows consistently by large. I
> don't get why kernel has to return something without seeing a very
> convincing use case?
>
> Not to mention spec doesn't give us explicit definition for when the
> field in config space becomes valid and/or the default value at first
> sights as part of feature negotiation. If we want to stick to the model
> Lingshan proposed, maybe fix the spec first then get back on the details?

So spec said

"
The following driver-read-only field, max_virtqueue_pairs only exists
if VIRTIO_NET_F_MQ or VIRTIO_NET_F_RSS is set.
"

My understanding is that the field is always valid if the device
offers the feature.

Btw, even if the spec is unclear, it would be very hard to "fix" it
without introducing a new feature bit, it means we still need to deal
with device without the new feature.

Thanks

>
> -Siwei
>
> >
> > And I like it that this fixes sparse warning actually:
> > max_virtqueue_pairs it tagged as __virtio, not __le.
> >
> > However, I am worried there is another bug here:
> > this is checking driver features. But really max vqs
> > should not depend on that, it depends on device
> > features, no?
> >
> >
> >
> >>> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
> >>> ---
> >>>   drivers/vdpa/vdpa.c | 7 ++++---
> >>>   1 file changed, 4 insertions(+), 3 deletions(-)
> >>>
> >>> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c index
> >>> d76b22b2f7ae..846dd37f3549 100644
> >>> --- a/drivers/vdpa/vdpa.c
> >>> +++ b/drivers/vdpa/vdpa.c
> >>> @@ -806,9 +806,10 @@ static int vdpa_dev_net_mq_config_fill(struct
> >>> vdpa_device *vdev,
> >>>     u16 val_u16;
> >>>
> >>>     if ((features & BIT_ULL(VIRTIO_NET_F_MQ)) == 0)
> >>> -           return 0;
> >>> +           val_u16 = 1;
> >>> +   else
> >>> +           val_u16 = __virtio16_to_cpu(true, config-
> >>>> max_virtqueue_pairs);
> >>> -   val_u16 = le16_to_cpu(config->max_virtqueue_pairs);
> >>>     return nla_put_u16(msg, VDPA_ATTR_DEV_NET_CFG_MAX_VQP,
> >>> val_u16);  }
> >>>
> >>> @@ -842,7 +843,7 @@ static int vdpa_dev_net_config_fill(struct
> >>> vdpa_device *vdev, struct sk_buff *ms
> >>>                           VDPA_ATTR_PAD))
> >>>             return -EMSGSIZE;
> >>>
> >>> -   return vdpa_dev_net_mq_config_fill(vdev, msg, features_driver,
> >>> &config);
> >>> +   return vdpa_dev_net_mq_config_fill(vdev, msg, features_device,
> >>> +&config);
> >>>   }
> >>>
> >>>   static int
> >>> --
> >>> 2.31.1
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>
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Re: [PATCH V4 5/6] vDPA: answer num of queue pairs = 1 to userspace when VIRTIO_NET_F_MQ == 0

[Si-Wei Liu]

On 8/9/2022 6:09 PM, Jason Wang wrote:
> On Wed, Aug 10, 2022 at 8:54 AM Si-Wei Liu <si-wei.liu@oracle.com> wrote:
>>
>>
>> On 8/9/2022 12:36 PM, Michael S. Tsirkin wrote:
>>> On Fri, Jul 22, 2022 at 01:14:42PM +0000, Parav Pandit wrote:
>>>>> From: Zhu Lingshan <lingshan.zhu@intel.com>
>>>>> Sent: Friday, July 22, 2022 7:53 AM
>>>>>
>>>>> If VIRTIO_NET_F_MQ == 0, the virtio device should have one queue pair, so
>>>>> when userspace querying queue pair numbers, it should return mq=1 than
>>>>> zero.
>>>>>
>>>>> Function vdpa_dev_net_config_fill() fills the attributions of the vDPA
>>>>> devices, so that it should call vdpa_dev_net_mq_config_fill() so the
>>>>> parameter in vdpa_dev_net_mq_config_fill() should be feature_device than
>>>>> feature_driver for the vDPA devices themselves
>>>>>
>>>>> Before this change, when MQ = 0, iproute2 output:
>>>>> $vdpa dev config show vdpa0
>>>>> vdpa0: mac 00:e8:ca:11:be:05 link up link_announce false max_vq_pairs 0
>>>>> mtu 1500
>>>>>
>>>>> After applying this commit, when MQ = 0, iproute2 output:
>>>>> $vdpa dev config show vdpa0
>>>>> vdpa0: mac 00:e8:ca:11:be:05 link up link_announce false max_vq_pairs 1
>>>>> mtu 1500
>>>>>
>>>> No. We do not want to diverge returning values of config space for fields which are not present as discussed in previous versions.
>>>> Please drop this patch.
>>>> Nack on this patch.
>>> Wrt this patch as far as I'm concerned you guys are bikeshedding.
>>>
>>> Parav generally don't send nacks please they are not helpful.
>>>
>>> Zhu Lingshan please always address comments in some way.  E.g. refer to
>>> them in the commit log explaining the motivation and the alternatives.
>>> I know you don't agree with Parav but ghosting isn't nice.
>>>
>>> I still feel what we should have done is
>>> not return a value, as long as we do return it we might
>>> as well return something reasonable, not 0.
>> Maybe I missed something but I don't get this, when VIRTIO_NET_F_MQ is
>> not negotiated, the VDPA_ATTR_DEV_NET_CFG_MAX_VQP attribute is simply
>> not there, but userspace (iproute) mistakenly puts a zero value there.
>> This is a pattern every tool in iproute follows consistently by large. I
>> don't get why kernel has to return something without seeing a very
>> convincing use case?
>>
>> Not to mention spec doesn't give us explicit definition for when the
>> field in config space becomes valid and/or the default value at first
>> sights as part of feature negotiation. If we want to stick to the model
>> Lingshan proposed, maybe fix the spec first then get back on the details?
> So spec said
>
> "
> The following driver-read-only field, max_virtqueue_pairs only exists
> if VIRTIO_NET_F_MQ or VIRTIO_NET_F_RSS is set.
> "
>
> My understanding is that the field is always valid if the device
> offers the feature.
The tricky part is to deal with VERSION_1 on transitional device that 
determines the endianness of field. I know we don't support !VERSION_1 
vdpa provider for now, but the tool should be made independent of this 
assumption.

For the most of config fields there's no actual valid "default" value 
during feature negotiation until it can be determined after negotiation 
is done. I wonder what is the administrative value if presenting those 
random value to the end user? And there's even special feature like 
VIRTIO_BLK_F_CONFIG_WCE that only present valid feature value after 
negotiation. I'm afraid it may further confuse end user, or it would 
require them to read and understand all of details in spec, which 
apparently contradict to the goal of showing meaningful queue-pair value 
without requiring user to read the spec details.

-Siwei

>
> Btw, even if the spec is unclear, it would be very hard to "fix" it
> without introducing a new feature bit, it means we still need to deal
> with device without the new feature.
>
> Thanks
>
>> -Siwei
>>
>>> And I like it that this fixes sparse warning actually:
>>> max_virtqueue_pairs it tagged as __virtio, not __le.
>>>
>>> However, I am worried there is another bug here:
>>> this is checking driver features. But really max vqs
>>> should not depend on that, it depends on device
>>> features, no?
>>>
>>>
>>>
>>>>> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
>>>>> ---
>>>>>    drivers/vdpa/vdpa.c | 7 ++++---
>>>>>    1 file changed, 4 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c index
>>>>> d76b22b2f7ae..846dd37f3549 100644
>>>>> --- a/drivers/vdpa/vdpa.c
>>>>> +++ b/drivers/vdpa/vdpa.c
>>>>> @@ -806,9 +806,10 @@ static int vdpa_dev_net_mq_config_fill(struct
>>>>> vdpa_device *vdev,
>>>>>      u16 val_u16;
>>>>>
>>>>>      if ((features & BIT_ULL(VIRTIO_NET_F_MQ)) == 0)
>>>>> -           return 0;
>>>>> +           val_u16 = 1;
>>>>> +   else
>>>>> +           val_u16 = __virtio16_to_cpu(true, config-
>>>>>> max_virtqueue_pairs);
>>>>> -   val_u16 = le16_to_cpu(config->max_virtqueue_pairs);
>>>>>      return nla_put_u16(msg, VDPA_ATTR_DEV_NET_CFG_MAX_VQP,
>>>>> val_u16);  }
>>>>>
>>>>> @@ -842,7 +843,7 @@ static int vdpa_dev_net_config_fill(struct
>>>>> vdpa_device *vdev, struct sk_buff *ms
>>>>>                            VDPA_ATTR_PAD))
>>>>>              return -EMSGSIZE;
>>>>>
>>>>> -   return vdpa_dev_net_mq_config_fill(vdev, msg, features_driver,
>>>>> &config);
>>>>> +   return vdpa_dev_net_mq_config_fill(vdev, msg, features_device,
>>>>> +&config);
>>>>>    }
>>>>>
>>>>>    static int
>>>>> --
>>>>> 2.31.1
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