linux-kernel - Re: [PATCH v2 1/2] iommu/arm-smmu-v3: Do not bother impl_ops if IOMMU_VIOMMU_TYPE_ARM

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Message-ID: <aH6TuLAz4DeoLByx@willie-the-truck>
Date: Mon, 21 Jul 2025 20:23:36 +0100
From: Will Deacon <will@...nel.org>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: jgg@...dia.com, joro@...tes.org, robin.murphy@....com,
	linux-arm-kernel@...ts.infradead.org, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org
Subject: Re: [PATCH v2 1/2] iommu/arm-smmu-v3: Do not bother impl_ops if
 IOMMU_VIOMMU_TYPE_ARM_SMMUV3

On Mon, Jul 21, 2025 at 12:12:35PM -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@...nel.org>
> Signed-off-by: Nicolin Chen <nicolinc@...dia.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(-)

Cheers for the quick respin.

> 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..dfe7f40fac35 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;
> +		}

I suppose that could be != instead of ^ to avoid mixing up logical and
arithmetic operators, but it does the trick either way so:

Acked-by: Will Deacon <will@...nel.org>

Will