Re: [PATCH v4 17/23] iommu/arm-smmu-v3-iommufd: Add vsmmu_alloc impl op

[Jason Gunthorpe <jgg@nvidia.com>]

On Thu, May 08, 2025 at 08:02:38PM -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 a vsmmu_alloc op and prioritize it in arm_vsmmu_alloc().
> 
> Reviewed-by: Pranjal Shrivastava <praan@google.com>
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h     |  6 ++++++
>  .../iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c | 17 +++++++++++------
>  2 files changed, 17 insertions(+), 6 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 6b8f0d20dac3..a5835af72417 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_smmu_domain;
>  
>  /* MMIO registers */
>  #define ARM_SMMU_IDR0			0x0
> @@ -720,6 +721,11 @@ 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);
> +	struct arm_vsmmu *(*vsmmu_alloc)(
> +		struct arm_smmu_device *smmu,
> +		struct arm_smmu_domain *smmu_domain, struct iommufd_ctx *ictx,
> +		unsigned int viommu_type,
> +		const struct iommu_user_data *user_data);
>  };

I think you should put the supported viommu type here in the ops
struct and match it here:

> +	/* Prioritize the impl that may support IOMMU_VIOMMU_TYPE_ARM_SMMUV3 */
> +	if (master->smmu->impl_ops && master->smmu->impl_ops->vsmmu_alloc)
> +		vsmmu = master->smmu->impl_ops->vsmmu_alloc(
> +			master->smmu, s2_parent, ictx, viommu_type, user_data);

instead of the EOPNOTSUPP dance. Either the impl_ops supports the
requested viommu as an extension or we are running in the normal mode?

Is there a reason to allocate a different viommu if the userspace does
not enable the implementation specific features?

Jason