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

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Date:   Wed, 13 Jul 2022 01:31:26 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Zhu Lingshan <lingshan.zhu@...el.com>
Cc:     jasowang@...hat.com, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, parav@...dia.com, xieyongji@...edance.com,
        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 01, 2022 at 09:28:21PM +0800, Zhu Lingshan 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 | 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;

There's a min macro for this.

> 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