Re: [PATCH 6/8] iommu/arm-smmu-v3: Implement IOMMU_HWPT_ALLOC_NEST_PARENT

[Robin Murphy <robin.murphy@arm.com>]

On 2024-08-07 12:41 am, Jason Gunthorpe wrote:
> For SMMUv3 the parent must be a S2 domain, which can be composed
> into a IOMMU_DOMAIN_NESTED.
> 
> In future the S2 parent will also need a VMID linked to the VIOMMU and
> even to KVM.
> 
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> ---
>   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 11 ++++++++++-
>   1 file changed, 10 insertions(+), 1 deletion(-)
> 
> 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 6bbe4aa7b9511c..5faaccef707ef1 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -3103,7 +3103,8 @@ arm_smmu_domain_alloc_user(struct device *dev, u32 flags,
>   			   const struct iommu_user_data *user_data)
>   {
>   	struct arm_smmu_master *master = dev_iommu_priv_get(dev);
> -	const u32 PAGING_FLAGS = IOMMU_HWPT_ALLOC_DIRTY_TRACKING;
> +	const u32 PAGING_FLAGS = IOMMU_HWPT_ALLOC_DIRTY_TRACKING |
> +				 IOMMU_HWPT_ALLOC_NEST_PARENT;
>   	struct arm_smmu_domain *smmu_domain;
>   	int ret;
>   
> @@ -3116,6 +3117,14 @@ arm_smmu_domain_alloc_user(struct device *dev, u32 flags,
>   	if (!smmu_domain)
>   		return ERR_PTR(-ENOMEM);
>   
> +	if (flags & IOMMU_HWPT_ALLOC_NEST_PARENT) {
> +		if (!(master->smmu->features & ARM_SMMU_FEAT_TRANS_S2)) {

Nope, nesting needs to rely on FEAT_NESTING, that's why it exists. S2 
alone isn't sufficient - without S1 there's nothing to expose to 
userspace, so zero point in having a "nested" domain with nothing to 
nest into it - but furthermore we need S2 *without* unsafe broken TLBs.

Thanks,
Robin.

> +			ret = -EOPNOTSUPP;
> +			goto err_free;
> +		}
> +		smmu_domain->stage = ARM_SMMU_DOMAIN_S2;
> +	}
> +
>   	smmu_domain->domain.type = IOMMU_DOMAIN_UNMANAGED;
>   	smmu_domain->domain.ops = arm_smmu_ops.default_domain_ops;
>   	ret = arm_smmu_domain_finalise(smmu_domain, master->smmu, flags);