RE: [PATCH RFC 01/11] iommu: Add pasid_bits field in struct dev_iommu

[Tian, Kevin]

> From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> Sent: Sunday, March 20, 2022 2:40 PM
> 
> Use this field to save the pasid/ssid bits that a device is able to
> support with its IOMMU hardware. It is a generic attribute of a device
> and lifting it into the per-device dev_iommu struct makes it possible
> to allocate a PASID for device without calls into the IOMMU drivers.
> Any iommu driver which suports PASID related features should set this
> field before features are enabled on the devices.
> 
> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> ---
>  include/linux/iommu.h                       | 1 +
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 1 +
>  drivers/iommu/intel/iommu.c                 | 5 ++++-
>  3 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 6ef2df258673..36f43af0af53 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -368,6 +368,7 @@ struct dev_iommu {
>  	struct iommu_fwspec		*fwspec;
>  	struct iommu_device		*iommu_dev;
>  	void				*priv;
> +	unsigned int			pasid_bits;
>  };
> 
>  int iommu_device_register(struct iommu_device *iommu,
> 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 627a3ed5ee8f..8e262210b5ad 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -2812,6 +2812,7 @@ static int arm_smmu_dev_enable_feature(struct
> device *dev,
>  		master->iopf_enabled = true;
>  		return 0;
>  	case IOMMU_DEV_FEAT_SVA:
> +		dev->iommu->pasid_bits = master->ssid_bits;
>  		return arm_smmu_master_enable_sva(master);
>  	default:
>  		return -EINVAL;
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 6f7485c44a4b..c1b91bce1530 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -4587,8 +4587,11 @@ static struct iommu_device
> *intel_iommu_probe_device(struct device *dev)
>  			if (pasid_supported(iommu)) {
>  				int features = pci_pasid_features(pdev);
> 
> -				if (features >= 0)
> +				if (features >= 0) {
>  					info->pasid_supported = features | 1;
> +					dev->iommu->pasid_bits =
> +						fls(pci_max_pasids(pdev)) - 1;

Original intel_svm_alloc_pasid() covers both PCI and non-PCI devices:

	ioasid_t max_pasid = dev_is_pci(dev) ?
		pci_max_pasids(to_pci_dev(dev)) : intel_pasid_max_id;

though I'm not sure whether non-PCI SVA has been supported indeed, this
patch implies a functional change here.

> +				}
>  			}
> 
>  			if (info->ats_supported && ecap_prs(iommu->ecap)
> &&
> --
> 2.25.1