linux-kernel - Re: [PATCH v9 1/4] iommu: Move def_domain type check for untrusted device into core

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Date:   Mon, 23 Nov 2020 12:04:50 +0000
From:   Will Deacon <will@...nel.org>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>, Ashok Raj <ashok.raj@...el.com>,
        Christoph Hellwig <hch@....de>,
        Sohil Mehta <sohil.mehta@...el.com>,
        Robin Murphy <robin.murphy@....com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Shameerali Kolothum Thodi 
        <shameerali.kolothum.thodi@...wei.com>
Subject: Re: [PATCH v9 1/4] iommu: Move def_domain type check for untrusted
 device into core

On Sat, Nov 21, 2020 at 09:56:17PM +0800, Lu Baolu wrote:
> So that the vendor iommu drivers are no more required to provide the
> def_domain_type callback to always isolate the untrusted devices.
> 
> Link: https://lore.kernel.org/linux-iommu/243ce89c33fe4b9da4c56ba35acebf81@huawei.com/
> Cc: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> ---
>  drivers/iommu/intel/iommu.c |  7 -------
>  drivers/iommu/iommu.c       | 21 ++++++++++++++-------
>  2 files changed, 14 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index af3abd285214..6711f78141a4 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -2916,13 +2916,6 @@ static int device_def_domain_type(struct device *dev)
>  	if (dev_is_pci(dev)) {
>  		struct pci_dev *pdev = to_pci_dev(dev);
>  
> -		/*
> -		 * Prevent any device marked as untrusted from getting
> -		 * placed into the statically identity mapping domain.
> -		 */
> -		if (pdev->untrusted)
> -			return IOMMU_DOMAIN_DMA;
> -
>  		if ((iommu_identity_mapping & IDENTMAP_AZALIA) && IS_AZALIA(pdev))
>  			return IOMMU_DOMAIN_IDENTITY;
>  
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 88b0c9192d8c..3256784c0358 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -1457,13 +1457,23 @@ struct iommu_group *fsl_mc_device_group(struct device *dev)
>  }
>  EXPORT_SYMBOL_GPL(fsl_mc_device_group);
>  
> -static int iommu_get_def_domain_type(struct device *dev)
> +/* Get the mandatary def_domain type for device. Otherwise, return 0. */
> +static int iommu_get_mandatory_def_domain_type(struct device *dev)
>  {
>  	const struct iommu_ops *ops = dev->bus->iommu_ops;
> -	unsigned int type = 0;
> +
> +	if (dev_is_pci(dev) && to_pci_dev(dev)->untrusted)
> +		return IOMMU_DOMAIN_DMA;
>  
>  	if (ops->def_domain_type)
> -		type = ops->def_domain_type(dev);
> +		return ops->def_domain_type(dev);
> +
> +	return 0;
> +}
> +
> +static int iommu_get_def_domain_type(struct device *dev)
> +{
> +	int type = iommu_get_mandatory_def_domain_type(dev);
>  
>  	return (type == 0) ? iommu_def_domain_type : type;
>  }
> @@ -1645,13 +1655,10 @@ struct __group_domain_type {
>  
>  static int probe_get_default_domain_type(struct device *dev, void *data)
>  {
> -	const struct iommu_ops *ops = dev->bus->iommu_ops;
>  	struct __group_domain_type *gtype = data;
>  	unsigned int type = 0;
>  
> -	if (ops->def_domain_type)
> -		type = ops->def_domain_type(dev);
> -
> +	type = iommu_get_mandatory_def_domain_type(dev);

afaict, this code is only called from probe_alloc_default_domain(), which
has:

        /* Ask for default domain requirements of all devices in the group */
        __iommu_group_for_each_dev(group, &gtype,
                                   probe_get_default_domain_type);

        if (!gtype.type)
                gtype.type = iommu_def_domain_type;

so is there actually a need to introduce the new
iommu_get_mandatory_def_domain_type() function, given that a type of 0
always ends up resolving to the default domain type?

Will