linux-kernel - Re: [PATCH v6 20/25] iommu/arm-smmu-v3-iommufd: Add hw_info to impl

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Message-ID: <aFP4zHIVT6epJeLb@google.com>
Date: Thu, 19 Jun 2025 11:47:24 +0000
From: Pranjal Shrivastava <praan@...gle.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: jgg@...dia.com, kevin.tian@...el.com, corbet@....net, will@...nel.org,
	bagasdotme@...il.com, robin.murphy@....com, joro@...tes.org,
	thierry.reding@...il.com, vdumpa@...dia.com, jonathanh@...dia.com,
	shuah@...nel.org, jsnitsel@...hat.com, nathan@...nel.org,
	peterz@...radead.org, yi.l.liu@...el.com, mshavit@...gle.com,
	zhangzekun11@...wei.com, iommu@...ts.linux.dev,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-tegra@...r.kernel.org,
	linux-kselftest@...r.kernel.org, patches@...ts.linux.dev,
	mochs@...dia.com, alok.a.tiwari@...cle.com, vasant.hegde@....com,
	dwmw2@...radead.org, baolu.lu@...ux.intel.com
Subject: Re: [PATCH v6 20/25] iommu/arm-smmu-v3-iommufd: Add hw_info to
 impl_ops

On Sat, Jun 14, 2025 at 12:14:45AM -0700, Nicolin Chen wrote:
> This will be used by Tegra241 CMDQV implementation to report a non-default
> HW info data.
> 
> Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
> Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h         | 1 +
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c | 8 ++++++--
>  2 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> index 07589350b2a1..c408a035e65d 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> @@ -721,6 +721,7 @@ struct arm_smmu_impl_ops {
>  	int (*init_structures)(struct arm_smmu_device *smmu);
>  	struct arm_smmu_cmdq *(*get_secondary_cmdq)(
>  		struct arm_smmu_device *smmu, struct arm_smmu_cmdq_ent *ent);
> +	void *(*hw_info)(struct arm_smmu_device *smmu, u32 *length, u32 *type);
>  	const size_t vsmmu_size;
>  	const enum iommu_viommu_type vsmmu_type;
>  	int (*vsmmu_init)(struct arm_vsmmu *vsmmu,
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
> index 445365ae19e0..1c138aff73d1 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
> @@ -10,13 +10,17 @@
>  void *arm_smmu_hw_info(struct device *dev, u32 *length, u32 *type)
>  {
>  	struct arm_smmu_master *master = dev_iommu_priv_get(dev);
> +	const struct arm_smmu_impl_ops *impl_ops = master->smmu->impl_ops;
>  	struct iommu_hw_info_arm_smmuv3 *info;
>  	u32 __iomem *base_idr;
>  	unsigned int i;
>  
>  	if (*type != IOMMU_HW_INFO_TYPE_DEFAULT &&
> -	    *type != IOMMU_HW_INFO_TYPE_ARM_SMMUV3)
> -		return ERR_PTR(-EOPNOTSUPP);
> +	    *type != IOMMU_HW_INFO_TYPE_ARM_SMMUV3) {
> +		if (!impl_ops || !impl_ops->hw_info)
> +			return ERR_PTR(-EOPNOTSUPP);
> +		return impl_ops->hw_info(master->smmu, length, type);
> +	}

I'm not sure if I get this right.. if the user (while porting a VMM or
something) mistakenly passes *type == IOMMU_HW_INFO_TYPE_INTEL_VTD here,
they'll get impl-specific info? I agree in that case the impl-specific
driver needs to check the type, but shouldn't we simply return from here
itself if the type isn't arm-smmu-v3?

>  
>  	info = kzalloc(sizeof(*info), GFP_KERNEL);
>  	if (!info)
> -- 
> 2.43.0
>