Re: [PATCH v3 1/2] iommu/arm-smmu-v3: Do not bother impl_ops if IOMMU_VIOMMU_TYPE_ARM_SMMUV3

[Pranjal Shrivastava <praan@google.com>]

On Mon, Jul 21, 2025 at 01:04:43PM -0700, Nicolin Chen wrote:
> When viommu type is IOMMU_VIOMMU_TYPE_ARM_SMMUV3, always return or init the
> standard struct arm_vsmmu, instead of going through impl_ops that must have
> its own viommu type than the standard IOMMU_VIOMMU_TYPE_ARM_SMMUV3.
> 
> Given that arm_vsmmu_init() is called after arm_smmu_get_viommu_size(), any
> unsupported viommu->type must be a corruption. And it must be a driver bug
> that its vsmmu_size and vsmmu_init ops aren't paired. Warn these two cases.
> 
> Suggested-by: Will Deacon <will@kernel.org>
> Acked-by: Will Deacon <will@kernel.org>
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>

Reviewed-by: Pranjal Shrivastava <praan@google.com>

> ---
>  .../arm/arm-smmu-v3/arm-smmu-v3-iommufd.c     | 24 ++++++++++---------
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c   | 14 +++++++++++
>  2 files changed, 27 insertions(+), 11 deletions(-)
> 
> 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 d9bea8f1f636..c034d6c5468f 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
> @@ -420,14 +420,13 @@ size_t arm_smmu_get_viommu_size(struct device *dev,
>  	    !(smmu->features & ARM_SMMU_FEAT_S2FWB))
>  		return 0;
>  
> -	if (smmu->impl_ops && smmu->impl_ops->vsmmu_size &&
> -	    viommu_type == smmu->impl_ops->vsmmu_type)
> -		return smmu->impl_ops->vsmmu_size;
> +	if (viommu_type == IOMMU_VIOMMU_TYPE_ARM_SMMUV3)
> +		return VIOMMU_STRUCT_SIZE(struct arm_vsmmu, core);
>  
> -	if (viommu_type != IOMMU_VIOMMU_TYPE_ARM_SMMUV3)
> +	if (!smmu->impl_ops || !smmu->impl_ops->vsmmu_size ||
> +	    viommu_type != smmu->impl_ops->vsmmu_type)
>  		return 0;
> -
> -	return VIOMMU_STRUCT_SIZE(struct arm_vsmmu, core);
> +	return smmu->impl_ops->vsmmu_size;
>  }
>  
>  int arm_vsmmu_init(struct iommufd_viommu *viommu,
> @@ -447,12 +446,15 @@ int arm_vsmmu_init(struct iommufd_viommu *viommu,
>  	/* FIXME Move VMID allocation from the S2 domain allocation to here */
>  	vsmmu->vmid = s2_parent->s2_cfg.vmid;
>  
> -	if (smmu->impl_ops && smmu->impl_ops->vsmmu_init &&
> -	    viommu->type == smmu->impl_ops->vsmmu_type)
> -		return smmu->impl_ops->vsmmu_init(vsmmu, user_data);
> +	if (viommu->type == IOMMU_VIOMMU_TYPE_ARM_SMMUV3) {
> +		viommu->ops = &arm_vsmmu_ops;
> +		return 0;
> +	}
>  
> -	viommu->ops = &arm_vsmmu_ops;
> -	return 0;
> +	/* Unsupported type was rejected in arm_smmu_get_viommu_size() */
> +	if (WARN_ON(viommu->type != smmu->impl_ops->vsmmu_type))
> +		return -EOPNOTSUPP;
> +	return smmu->impl_ops->vsmmu_init(vsmmu, user_data);
>  }
>  
>  int arm_vmaster_report_event(struct arm_smmu_vmaster *vmaster, u64 *evt)
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> index 181d07bc1a9d..9f4ad3705801 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -4703,6 +4703,7 @@ static void arm_smmu_impl_remove(void *data)
>  static struct arm_smmu_device *arm_smmu_impl_probe(struct arm_smmu_device *smmu)
>  {
>  	struct arm_smmu_device *new_smmu = ERR_PTR(-ENODEV);
> +	const struct arm_smmu_impl_ops *ops;
>  	int ret;
>  
>  	if (smmu->impl_dev && (smmu->options & ARM_SMMU_OPT_TEGRA241_CMDQV))
> @@ -4713,11 +4714,24 @@ static struct arm_smmu_device *arm_smmu_impl_probe(struct arm_smmu_device *smmu)
>  	if (IS_ERR(new_smmu))
>  		return new_smmu;
>  
> +	ops = new_smmu->impl_ops;
> +	if (ops) {
> +		/* vsmmu_size and vsmmu_init ops must be paired */
> +		if (WARN_ON(!ops->vsmmu_size != !ops->vsmmu_init)) {
> +			ret = -EINVAL;
> +			goto err_remove;
> +		}
> +	}
> +
>  	ret = devm_add_action_or_reset(new_smmu->dev, arm_smmu_impl_remove,
>  				       new_smmu);
>  	if (ret)
>  		return ERR_PTR(ret);
>  	return new_smmu;
> +
> +err_remove:
> +	arm_smmu_impl_remove(new_smmu);
> +	return ERR_PTR(ret);
>  }
>  
>  static int arm_smmu_device_probe(struct platform_device *pdev)
> -- 
> 2.43.0
> 
>