RE: [PATCH] iommufd: Enforce IOMMU_RESV_SW_MSI upon hwpt_paging allocation

[Tian, Kevin]

> From: Nicolin Chen <nicolinc@xxxxxxxxxx>
> Sent: Thursday, August 1, 2024 5:22 AM
> 
> @@ -316,7 +316,9 @@ static inline bool hwpt_is_paging(struct
> iommufd_hw_pagetable *hwpt)
>  static inline struct iommufd_hwpt_paging *
>  to_hwpt_paging(struct iommufd_hw_pagetable *hwpt)
>  {
> -	return container_of(hwpt, struct iommufd_hwpt_paging, common);
> +	if (hwpt_is_paging(hwpt))
> +		return container_of(hwpt, struct iommufd_hwpt_paging,
> common);
> +	return container_of(hwpt, struct iommufd_hwpt_nested, common)-
> >parent;
>  }
> 

hmm this doesn't work with future new hwpt types.

It's clearer to pass hwpt into earlier helpers and then do the type check
insided and make it a nop for types other than paging/nesting.