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

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Date:   Tue, 26 Jul 2022 11:06:51 +0000
From:   Parav Pandit <parav@...dia.com>
To:     "Zhu, Lingshan" <lingshan.zhu@...el.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "mst@...hat.com" <mst@...hat.com>
CC:     "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "xieyongji@...edance.com" <xieyongji@...edance.com>,
        "gautam.dawar@....com" <gautam.dawar@....com>
Subject: RE: [PATCH V4 3/6] vDPA: allow userspace to query features of a vDPA
 device


> From: Zhu, Lingshan <lingshan.zhu@...el.com>
> Sent: Tuesday, July 26, 2022 7:03 AM
> 
> On 7/24/2022 11:21 PM, Parav Pandit wrote:
> >
> >> From: Zhu, Lingshan <lingshan.zhu@...el.com>
> >> Sent: Saturday, July 23, 2022 7:24 AM
> >>
> >>
> >> On 7/22/2022 9:12 PM, Parav Pandit wrote:
> >>>> From: Zhu Lingshan <lingshan.zhu@...el.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@...el.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.