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

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Date:   Thu, 2 Jun 2022 15:36:23 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Zhu Lingshan <lingshan.zhu@...el.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 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.

Thanks

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