linux-kernel - Re: [PATCH v3 2/4] iommu: Add iommu_aux_at(de)tach

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Message-ID: <b5b22e01-4a51-8dfe-9ba4-aeca783740f1@linux.intel.com>
Date:   Wed, 15 Jul 2020 08:47:36 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, kvm@...r.kernel.org,
        Cornelia Huck <cohuck@...hat.com>,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH v3 2/4] iommu: Add iommu_aux_at(de)tach_group()

Hi Jacob,

On 7/15/20 12:39 AM, Jacob Pan wrote:
> On Tue, 14 Jul 2020 13:57:01 +0800
> Lu Baolu<baolu.lu@...ux.intel.com>  wrote:
> 
>> This adds two new aux-domain APIs for a use case like vfio/mdev where
>> sub-devices derived from an aux-domain capable device are created and
>> put in an iommu_group.
>>
>> /**
>>   * iommu_aux_attach_group - attach an aux-domain to an iommu_group
>> which
>>   *                          contains sub-devices (for example mdevs)
>> derived
>>   *                          from @dev.
>>   * @domain: an aux-domain;
>>   * @group:  an iommu_group which contains sub-devices derived from
>> @dev;
>>   * @dev:    the physical device which supports IOMMU_DEV_FEAT_AUX.
>>   *
>>   * Returns 0 on success, or an error value.
>>   */
>> int iommu_aux_attach_group(struct iommu_domain *domain,
>>                             struct iommu_group *group,
>>                             struct device *dev)
>>
>> /**
>>   * iommu_aux_detach_group - detach an aux-domain from an iommu_group
>>   *
>>   * @domain: an aux-domain;
>>   * @group:  an iommu_group which contains sub-devices derived from
>> @dev;
>>   * @dev:    the physical device which supports IOMMU_DEV_FEAT_AUX.
>>   *
>>   * @domain must have been attached to @group via
>> iommu_aux_attach_group(). */
>> void iommu_aux_detach_group(struct iommu_domain *domain,
>>                              struct iommu_group *group,
>>                              struct device *dev)
>>
>> It also adds a flag in the iommu_group data structure to identify
>> an iommu_group with aux-domain attached from those normal ones.
>>
>> Signed-off-by: Lu Baolu<baolu.lu@...ux.intel.com>
>> ---
>>   drivers/iommu/iommu.c | 58
>> +++++++++++++++++++++++++++++++++++++++++++ include/linux/iommu.h |
>> 17 +++++++++++++ 2 files changed, 75 insertions(+)
>>
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index e1fdd3531d65..cad5a19ebf22 100644
>> --- a/drivers/iommu/iommu.c
>> +++ b/drivers/iommu/iommu.c
>> @@ -45,6 +45,7 @@ struct iommu_group {
>>   	struct iommu_domain *default_domain;
>>   	struct iommu_domain *domain;
>>   	struct list_head entry;
>> +	unsigned int aux_domain_attached:1;
>>   };
>>   
>>   struct group_device {
>> @@ -2759,6 +2760,63 @@ int iommu_aux_get_pasid(struct iommu_domain
>> *domain, struct device *dev) }
>>   EXPORT_SYMBOL_GPL(iommu_aux_get_pasid);
>>   
>> +/**
>> + * iommu_aux_attach_group - attach an aux-domain to an iommu_group
>> which
>> + *                          contains sub-devices (for example mdevs)
>> derived
>> + *                          from @dev.
>> + * @domain: an aux-domain;
>> + * @group:  an iommu_group which contains sub-devices derived from
>> @dev;
>> + * @dev:    the physical device which supports IOMMU_DEV_FEAT_AUX.
>> + *
>> + * Returns 0 on success, or an error value.
>> + */
>> +int iommu_aux_attach_group(struct iommu_domain *domain,
>> +			   struct iommu_group *group, struct device
>> *dev) +{
>> +	int ret = -EBUSY;
>> +
>> +	mutex_lock(&group->mutex);
>> +	if (group->domain)
>> +		goto out_unlock;
>> +
> Perhaps I missed something but are we assuming only one mdev per mdev
> group? That seems to change the logic where vfio does:
> iommu_group_for_each_dev()
> 	iommu_aux_attach_device()
> 

It has been changed in PATCH 4/4:

static int vfio_iommu_attach_group(struct vfio_domain *domain,
                                    struct vfio_group *group)
{
         if (group->mdev_group)
                 return iommu_aux_attach_group(domain->domain,
                                               group->iommu_group,
                                               group->iommu_device);
         else
                 return iommu_attach_group(domain->domain, 
group->iommu_group);
}

So, for both normal domain and aux-domain, we use the same concept:
attach a domain to a group.

Best regards,
baolu