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

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Message-ID: <CACGkMEsdKaWjmOncpLo1MO1DM2KDpE61KbH8uKBrnCqCxFubvw@mail.gmail.com>
Date:   Thu, 2 Jun 2022 15:11:09 +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 1/6] vDPA/ifcvf: get_config_size should return a value no
 greater than dev implementation

On Thu, Jun 2, 2022 at 10:48 AM 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.
>
> Signed-off-by: Zhu Lingshan <lingshan.zhu@...el.com>
> ---
>  drivers/vdpa/ifcvf/ifcvf_base.c | 8 ++++++--
>  drivers/vdpa/ifcvf/ifcvf_base.h | 2 ++
>  2 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/vdpa/ifcvf/ifcvf_base.c b/drivers/vdpa/ifcvf/ifcvf_base.c
> index 48c4dadb0c7c..6bccc8291c26 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);

One possible issue here is that, if the hardware have more size than
spec, we may end up with a migration compatibility issue.

It looks to me we'd better build the config size based on the
features, e.g it looks to me for net, we should probably use

offset_of(struct virtio_net_config, mtu)?

>                         IFCVF_DBG(pdev, "hw->dev_cfg = %p\n", hw->dev_cfg);
>                         break;
>                 }
> @@ -233,15 +234,18 @@ 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);
>         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;

I don't get the code here, any chance that net_config_size could be zero?

Thanks

>                 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
>