vDPA: !FEATURES_OK should not block querying device config space

Users may want to query the config space of a vDPA device,
to choose a appropriate one for a certain guest. This means the
users need to read the config space before FEATURES_OK, and
the existence of config space contents does not depend on
FEATURES_OK.

The spec says:
The device MUST allow reading of any device-specific configuration
field before FEATURES_OK is set by the driver. This includes
fields which are conditional on feature bits, as long as those
feature bits are offered by the device.
Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
Message-Id: <20220722115309.82746-5-lingshan.zhu@intel.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/vdpa/vdpa.c

@@ -846,17 +846,9 @@ vdpa_dev_config_fill(struct vdpa_device *vdev, struct sk_buff *msg, u32 portid,
 {
 	u32 device_id;
 	void *hdr;
-	u8 status;
 	int err;
 
 	down_read(&vdev->cf_lock);
-	status = vdev->config->get_status(vdev);
-	if (!(status & VIRTIO_CONFIG_S_FEATURES_OK)) {
-		NL_SET_ERR_MSG_MOD(extack, "Features negotiation not completed");
-		err = -EAGAIN;
-		goto out;
-	}
-
 	hdr = genlmsg_put(msg, portid, seq, &vdpa_nl_family, flags,
 			  VDPA_CMD_DEV_CONFIG_GET);
 	if (!hdr) {