linux-kernel - Re: [PATCH v9 23/29] iommu/arm-smmu-v3-iommufd: Add vsmmu_size/type and vsmmu

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Message-ID: <aHE4Y-fbucm-j-yi@willie-the-truck>
Date: Fri, 11 Jul 2025 17:14:27 +0100
From: Will Deacon <will@...nel.org>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: jgg@...dia.com, kevin.tian@...el.com, corbet@....net,
	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,
	praan@...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 v9 23/29] iommu/arm-smmu-v3-iommufd: Add vsmmu_size/type
 and vsmmu_init impl ops

Hey Nicolin,

On Wed, Jul 09, 2025 at 10:59:15PM -0700, Nicolin Chen wrote:
> An impl driver might want to allocate its own type of vIOMMU object or the
> standard IOMMU_VIOMMU_TYPE_ARM_SMMUV3 by setting up its own SW/HW bits, as
> the tegra241-cmdqv driver will add IOMMU_VIOMMU_TYPE_TEGRA241_CMDQV.
> 
> Add vsmmu_size/type and vsmmu_init to struct arm_smmu_impl_ops. Prioritize
> them in arm_smmu_get_viommu_size() and arm_vsmmu_init().
> 
> Reviewed-by: Pranjal Shrivastava <praan@...gle.com>
> Reviewed-by: Kevin Tian <kevin.tian@...el.com>
> 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         | 5 +++++
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c | 8 ++++++++
>  2 files changed, 13 insertions(+)
> 
> 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 c1ced4d4b6d1..6183f212539a 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> @@ -16,6 +16,7 @@
>  #include <linux/sizes.h>
>  
>  struct arm_smmu_device;
> +struct arm_vsmmu;
>  
>  /* MMIO registers */
>  #define ARM_SMMU_IDR0			0x0
> @@ -720,6 +721,10 @@ 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);
> +	const size_t vsmmu_size;
> +	const enum iommu_viommu_type vsmmu_type;
> +	int (*vsmmu_init)(struct arm_vsmmu *vsmmu,
> +			  const struct iommu_user_data *user_data);

It would be nice to avoid adding data members to the ops structure, if
at all possible. The easiest thing would probably be to add a function
for getting the vsmmu size and then pushing the two checks against
'vsmmu_type' down into the impl_ops callbacks so that:

  1. If the type is IOMMU_VIOMMU_TYPE_ARM_SMMUV3, we don't bother with
     the impl_ops at all in arm_vsmmu_init() and arm_smmu_get_viommu_size()

  2. Otherwise, we pass the type into the impl_ops and they can check it

Of course, that can be a patch on top of the series as there's no point
respinning the whole just for this.

Cheers,

Will