netdev - Re: [PATCH 4/6] vDPA: !FEATURES_OK should not block querying device config space

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Date:   Mon, 6 Jun 2022 16:19:52 +0800
From:   "Zhu, Lingshan" <lingshan.zhu@...el.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     mst <mst@...hat.com>,
        virtualization <virtualization@...ts.linux-foundation.org>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH 4/6] vDPA: !FEATURES_OK should not block querying device
 config space



On 6/2/2022 3:36 PM, Jason Wang wrote:
> On Thu, Jun 2, 2022 at 10:48 AM Zhu Lingshan <lingshan.zhu@...el.com> wrote:
>> 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.
> Quotes from the spec:
>
> "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."
>
>> This commit removes FEATURES_OK blocker in vdpa_dev_config_fill()
>> which calls vdpa_dev_net_config_fill() for virtio-net
>>
>> Signed-off-by: Zhu Lingshan <lingshan.zhu@...el.com>
>> ---
>>   drivers/vdpa/vdpa.c | 8 --------
>>   1 file changed, 8 deletions(-)
>>
>> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
>> index c820dd2b0307..030d96bdeed2 100644
>> --- a/drivers/vdpa/vdpa.c
>> +++ b/drivers/vdpa/vdpa.c
>> @@ -863,17 +863,9 @@ vdpa_dev_config_fill(struct vdpa_device *vdev, struct sk_buff *msg, u32 portid,
>>   {
>>          u32 device_id;
>>          void *hdr;
>> -       u8 status;
>>          int err;
>>
>>          mutex_lock(&vdev->cf_mutex);
>> -       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;
>> -       }
> So we had the following in vdpa_dev_net_config_fill():
>
>          features = vdev->config->get_driver_features(vdev);
>          if (nla_put_u64_64bit(msg, VDPA_ATTR_DEV_NEGOTIATED_FEATURES, features,
>                                VDPA_ATTR_PAD))
>                  return -EMSGSIZE;
>
> It looks to me we need to switch to using get_device_features() instead.
This is done in the 3/6 patch

Thanks,
ZHu Lingshan
>
> Thanks
>
>> -
>>          hdr = genlmsg_put(msg, portid, seq, &vdpa_nl_family, flags,
>>                            VDPA_CMD_DEV_CONFIG_GET);
>>          if (!hdr) {
>> --
>> 2.31.1
>>