linux-kernel - Re: [PATCH v4 17/23] iommu/arm-smmu-v3-iommufd: Add vsmmu

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Message-ID: <20250515171902.GO382960@nvidia.com>
Date: Thu, 15 May 2025 14:19:02 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: 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,
	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
Subject: Re: [PATCH v4 17/23] iommu/arm-smmu-v3-iommufd: Add vsmmu_alloc impl
 op

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@...gle.com>
> Signed-off-by: Nicolin Chen <nicolinc@...dia.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