Re: [PATCHv8 2/8] iommu/arm-smmu: Add domain attribute for pagetable configuration

[Will Deacon <will@kernel.org>]

On Tue, Nov 17, 2020 at 08:00:41PM +0530, Sai Prakash Ranjan wrote:
> Add iommu domain attribute for pagetable configuration which
> initially will be used to set quirks like for system cache aka
> last level cache to be used by client drivers like GPU to set
> right attributes for caching the hardware pagetables into the
> system cache and later can be extended to include other page
> table configuration data.
> 
> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
> ---
>  drivers/iommu/arm/arm-smmu/arm-smmu.c | 25 +++++++++++++++++++++++++
>  drivers/iommu/arm/arm-smmu/arm-smmu.h |  1 +
>  include/linux/io-pgtable.h            |  4 ++++
>  include/linux/iommu.h                 |  1 +
>  4 files changed, 31 insertions(+)
> 
> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> index 0f28a8614da3..7b05782738e2 100644
> --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> @@ -789,6 +789,9 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
>  	if (smmu_domain->non_strict)
>  		pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_NON_STRICT;
>  
> +	if (smmu_domain->pgtbl_cfg.quirks)
> +		pgtbl_cfg.quirks |= smmu_domain->pgtbl_cfg.quirks;
> +
>  	pgtbl_ops = alloc_io_pgtable_ops(fmt, &pgtbl_cfg, smmu_domain);
>  	if (!pgtbl_ops) {
>  		ret = -ENOMEM;
> @@ -1511,6 +1514,12 @@ static int arm_smmu_domain_get_attr(struct iommu_domain *domain,
>  		case DOMAIN_ATTR_NESTING:
>  			*(int *)data = (smmu_domain->stage == ARM_SMMU_DOMAIN_NESTED);
>  			return 0;
> +		case DOMAIN_ATTR_IO_PGTABLE_CFG: {
> +			struct domain_attr_io_pgtbl_cfg *pgtbl_cfg = data;
> +			*pgtbl_cfg = smmu_domain->pgtbl_cfg;
> +
> +			return 0;
> +		}
>  		default:
>  			return -ENODEV;
>  		}
> @@ -1551,6 +1560,22 @@ static int arm_smmu_domain_set_attr(struct iommu_domain *domain,
>  			else
>  				smmu_domain->stage = ARM_SMMU_DOMAIN_S1;
>  			break;
> +		case DOMAIN_ATTR_IO_PGTABLE_CFG: {
> +			struct domain_attr_io_pgtbl_cfg *pgtbl_cfg = data;
> +
> +			if (smmu_domain->smmu) {
> +				ret = -EPERM;
> +				goto out_unlock;
> +			}
> +
> +			if (!pgtbl_cfg) {

Do we really need to check this? If somebody passed us a NULL pointer then
they have a bug and we don't check this for other domain attributes afaict.

> +				ret = -ENODEV;
> +				goto out_unlock;
> +			}
> +
> +			smmu_domain->pgtbl_cfg = *pgtbl_cfg;
> +			break;
> +		}
>  		default:
>  			ret = -ENODEV;
>  		}
> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.h b/drivers/iommu/arm/arm-smmu/arm-smmu.h
> index 04288b6fc619..18fbed376afb 100644
> --- a/drivers/iommu/arm/arm-smmu/arm-smmu.h
> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.h
> @@ -364,6 +364,7 @@ enum arm_smmu_domain_stage {
>  struct arm_smmu_domain {
>  	struct arm_smmu_device		*smmu;
>  	struct io_pgtable_ops		*pgtbl_ops;
> +	struct domain_attr_io_pgtbl_cfg	pgtbl_cfg;
>  	const struct iommu_flush_ops	*flush_ops;
>  	struct arm_smmu_cfg		cfg;
>  	enum arm_smmu_domain_stage	stage;
> diff --git a/include/linux/io-pgtable.h b/include/linux/io-pgtable.h
> index a9a2c59fab37..686b37d48743 100644
> --- a/include/linux/io-pgtable.h
> +++ b/include/linux/io-pgtable.h
> @@ -212,6 +212,10 @@ struct io_pgtable {
>  
>  #define io_pgtable_ops_to_pgtable(x) container_of((x), struct io_pgtable, ops)
>  
> +struct domain_attr_io_pgtbl_cfg {
> +	unsigned long quirks;
> +};

nit: Can you rename this to 'struct io_pgtable_domain_attr' please?

Will