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Date:   Mon, 13 Jul 2020 14:14:54 +0100
From:   Will Deacon <will@kernel.org>
To:     Liu Yi L <yi.l.liu@intel.com>
Cc:     alex.williamson@redhat.com, eric.auger@redhat.com,
        baolu.lu@linux.intel.com, joro@8bytes.org, kevin.tian@intel.com,
        jacob.jun.pan@linux.intel.com, ashok.raj@intel.com,
        jun.j.tian@intel.com, yi.y.sun@intel.com, jean-philippe@linaro.org,
        peterx@redhat.com, hao.wu@intel.com, stefanha@gmail.com,
        iommu@lists.linux-foundation.org, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, Robin Murphy <robin.murphy@arm.com>
Subject: Re: [PATCH v5 03/15] iommu/smmu: Report empty domain nesting info
Message-ID: <20200713131454.GA2739@willie-the-truck>
References: <1594552870-55687-1-git-send-email-yi.l.liu@intel.com>
 <1594552870-55687-4-git-send-email-yi.l.liu@intel.com>
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On Sun, Jul 12, 2020 at 04:20:58AM -0700, Liu Yi L wrote:
> This patch is added as instead of returning a boolean for DOMAIN_ATTR_NESTING,
> iommu_domain_get_attr() should return an iommu_nesting_info handle.
> 
> Cc: Will Deacon <will@kernel.org>
> Cc: Robin Murphy <robin.murphy@arm.com>
> Cc: Eric Auger <eric.auger@redhat.com>
> Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>
> Suggested-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> ---
> v4 -> v5:
> *) address comments from Eric Auger.
> ---
>  drivers/iommu/arm-smmu-v3.c | 29 +++++++++++++++++++++++++++--
>  drivers/iommu/arm-smmu.c    | 29 +++++++++++++++++++++++++++--
>  2 files changed, 54 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> index f578677..ec815d7 100644
> --- a/drivers/iommu/arm-smmu-v3.c
> +++ b/drivers/iommu/arm-smmu-v3.c
> @@ -3019,6 +3019,32 @@ static struct iommu_group *arm_smmu_device_group(struct device *dev)
>  	return group;
>  }
>  
> +static int arm_smmu_domain_nesting_info(struct arm_smmu_domain *smmu_domain,
> +					void *data)
> +{
> +	struct iommu_nesting_info *info = (struct iommu_nesting_info *)data;
> +	unsigned int size;
> +
> +	if (!info || smmu_domain->stage != ARM_SMMU_DOMAIN_NESTED)
> +		return -ENODEV;
> +
> +	size = sizeof(struct iommu_nesting_info);
> +
> +	/*
> +	 * if provided buffer size is smaller than expected, should
> +	 * return 0 and also the expected buffer size to caller.
> +	 */
> +	if (info->size < size) {
> +		info->size = size;
> +		return 0;
> +	}
> +
> +	/* report an empty iommu_nesting_info for now */
> +	memset(info, 0x0, size);
> +	info->size = size;
> +	return 0;
> +}

Have you verified that this doesn't break the existing usage of
DOMAIN_ATTR_NESTING in drivers/vfio/vfio_iommu_type1.c?

Will