netdev - Re: [PATCH V3 1/6] vDPA/ifcvf: get_config_size should return a value no greater than dev implementation

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Message-ID: <CACGkMEvGo2urfPriS3f6dCxT+41KJ0E-KUd4-GvUrX81BVy8Og@mail.gmail.com>
Date:   Mon, 4 Jul 2022 12:39:35 +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>, Parav Pandit <parav@...dia.com>,
        Yongji Xie <xieyongji@...edance.com>,
        "Dawar, Gautam" <gautam.dawar@....com>
Subject: Re: [PATCH V3 1/6] vDPA/ifcvf: get_config_size should return a value
 no greater than dev implementation

On Fri, Jul 1, 2022 at 9:36 PM Zhu Lingshan <lingshan.zhu@...el.com> wrote:
>
> ifcvf_get_config_size() should return a virtio device type specific value,
> however the ret_value should not be greater than the onboard size of
> the device implementation. E.g., for virtio_net, config_size should be
> the minimum value of sizeof(struct virtio_net_config) and the onboard
> cap size.

Rethink of this, I wonder what's the value of exposing device
implementation details to users? Anyhow the parent is in charge of
"emulating" config space accessing.

If we do this, it's probably a blocker for cross vendor stuff.

Thanks

>
> Signed-off-by: Zhu Lingshan <lingshan.zhu@...el.com>
> ---
>  drivers/vdpa/ifcvf/ifcvf_base.c | 13 +++++++++++--
>  drivers/vdpa/ifcvf/ifcvf_base.h |  2 ++
>  2 files changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/vdpa/ifcvf/ifcvf_base.c b/drivers/vdpa/ifcvf/ifcvf_base.c
> index 48c4dadb0c7c..fb957b57941e 100644
> --- a/drivers/vdpa/ifcvf/ifcvf_base.c
> +++ b/drivers/vdpa/ifcvf/ifcvf_base.c
> @@ -128,6 +128,7 @@ int ifcvf_init_hw(struct ifcvf_hw *hw, struct pci_dev *pdev)
>                         break;
>                 case VIRTIO_PCI_CAP_DEVICE_CFG:
>                         hw->dev_cfg = get_cap_addr(hw, &cap);
> +                       hw->cap_dev_config_size = le32_to_cpu(cap.length);
>                         IFCVF_DBG(pdev, "hw->dev_cfg = %p\n", hw->dev_cfg);
>                         break;
>                 }
> @@ -233,15 +234,23 @@ int ifcvf_verify_min_features(struct ifcvf_hw *hw, u64 features)
>  u32 ifcvf_get_config_size(struct ifcvf_hw *hw)
>  {
>         struct ifcvf_adapter *adapter;
> +       u32 net_config_size = sizeof(struct virtio_net_config);
> +       u32 blk_config_size = sizeof(struct virtio_blk_config);
> +       u32 cap_size = hw->cap_dev_config_size;
>         u32 config_size;
>
>         adapter = vf_to_adapter(hw);
> +       /* If the onboard device config space size is greater than
> +        * the size of struct virtio_net/blk_config, only the spec
> +        * implementing contents size is returned, this is very
> +        * unlikely, defensive programming.
> +        */
>         switch (hw->dev_type) {
>         case VIRTIO_ID_NET:
> -               config_size = sizeof(struct virtio_net_config);
> +               config_size = cap_size >= net_config_size ? net_config_size : cap_size;
>                 break;
>         case VIRTIO_ID_BLOCK:
> -               config_size = sizeof(struct virtio_blk_config);
> +               config_size = cap_size >= blk_config_size ? blk_config_size : cap_size;
>                 break;
>         default:
>                 config_size = 0;
> diff --git a/drivers/vdpa/ifcvf/ifcvf_base.h b/drivers/vdpa/ifcvf/ifcvf_base.h
> index 115b61f4924b..f5563f665cc6 100644
> --- a/drivers/vdpa/ifcvf/ifcvf_base.h
> +++ b/drivers/vdpa/ifcvf/ifcvf_base.h
> @@ -87,6 +87,8 @@ struct ifcvf_hw {
>         int config_irq;
>         int vqs_reused_irq;
>         u16 nr_vring;
> +       /* VIRTIO_PCI_CAP_DEVICE_CFG size */
> +       u32 cap_dev_config_size;
>  };
>
>  struct ifcvf_adapter {
> --
> 2.31.1
>