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 21:54:49 +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 21:03, Will Deacon wrote:
> Hi Baolu,
> 
> On Mon, Nov 23, 2020 at 08:55:17PM +0800, Lu Baolu wrote:
>> On 2020/11/23 20:04, Will Deacon wrote:
>>> On Sat, Nov 21, 2020 at 09:56:17PM +0800, Lu Baolu wrote:
>>>> @@ -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.
> 
> I see, but isn't this also setting the default domain type in the case that
> it gets back a type of 0? I think it would be nice to avoid having both
> iommu_get_mandatory_def_domain_type() and iommu_get_def_domain_type() of we
> can, as it's really not clear which one to use when and what is meant by
> "mandatory" imo.

Yes, agreed. I will remove iommu_get_mandatory_def_domain_type() and
keep iommu_get_def_domain_type() as the only helper in the next version.

Best regards,
baolu