From: Zhu, Lingshan <redacted>
Sent: Wednesday, July 27, 2022 2:02 AM


On 7/26/2022 7:06 PM, Parav Pandit wrote:

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From: Zhu, Lingshan <redacted>
Sent: Tuesday, July 26, 2022 7:03 AM

On 7/24/2022 11:21 PM, Parav Pandit wrote:

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From: Zhu, Lingshan <redacted>
Sent: Saturday, July 23, 2022 7:24 AM


On 7/22/2022 9:12 PM, Parav Pandit wrote:

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From: Zhu Lingshan <redacted>
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

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features

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of vDPA devices through this new attr.

Signed-off-by: Zhu Lingshan <redacted>
---
    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

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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))

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    		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);

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+	return vdpa_dev_net_mq_config_fill(vdev, msg,

features_driver,

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+&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 */

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    	VDPA_ATTR_DEV_SUPPORTED_FEATURES,	/* u64 */
+	VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES,	/*

u64 */

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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"

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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.