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

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Message-ID: <5f6f0d5e-0cfc-2274-b186-180f50b8b1df@linux.intel.com>
Date:   Mon, 23 Nov 2020 20:55:17 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Will Deacon <will@...nel.org>
Cc:     baolu.lu@...ux.intel.com, 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

Hi Will,

On 2020/11/23 20:04, Will Deacon wrote:
> 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?

Another consumer of this helper is in the next patch:

+	dev_def_dom = iommu_get_mandatory_def_domain_type(dev);
+
+	/* Check if user requested domain is supported by the device or not */
+	if (!type) {
+		/*
+		 * If the user hasn't requested any specific type of domain and
+		 * if the device supports both the domains, then default to the
+		 * domain the device was booted with
+		 */
+		type = iommu_get_def_domain_type(dev);
+	} else if (dev_def_dom && type != dev_def_dom) {
+		dev_err_ratelimited(prev_dev, "Device cannot be in %s domain\n",
+				    iommu_domain_type_str(type));
+		ret = -EINVAL;
+		goto out;
+	}

I also added the untrusted device check in
iommu_get_mandatory_def_domain_type(), so that we don't need to care
about this in multiple places.

Best regards,
baolu