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Date:   Wed, 20 Sep 2023 13:41:07 +0800
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Subject: Re: [PATCH 6/6] iommu/vt-d: Add domain_alloc_user op
To:     Yi Liu <yi.l.liu@intel.com>, "joro@8bytes.org" <joro@8bytes.org>,
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References: <20230919092523.39286-1-yi.l.liu@intel.com>
 <20230919092523.39286-7-yi.l.liu@intel.com>
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From:   "Yang, Weijiang" <weijiang.yang@intel.com>
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On 9/19/2023 5:25 PM, Yi Liu wrote:
> This adds the domain_alloc_user op implementation. It supports allocating
> domains to be used as parent under nested translation.
>
> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> ---
>   drivers/iommu/intel/iommu.c | 20 ++++++++++++++++++++
>   1 file changed, 20 insertions(+)
>
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 5db283c17e0d..491bcde1ff96 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -4074,6 +4074,25 @@ static struct iommu_domain *intel_iommu_domain_alloc(unsigned type)
>   	return NULL;
>   }
>   
> +static struct iommu_domain *
> +intel_iommu_domain_alloc_user(struct device *dev, u32 flags)
> +{
> +	struct iommu_domain *domain;
> +	struct intel_iommu *iommu;
> +
> +	iommu = device_to_iommu(dev, NULL, NULL);
> +	if (!iommu)
> +		return ERR_PTR(-ENODEV);
> +
> +	if ((flags & IOMMU_HWPT_ALLOC_NEST_PARENT) && !ecap_nest(iommu->ecap))
> +		return ERR_PTR(-EOPNOTSUPP);

The outer caller has checked (flags & IOMMU_HWPT_ALLOC_NEST_PARENT) before it comes here.
If this callback is dedicated for nested domain allocation, then you may omit the condition here.