Re: [PATCH RFC v2 03/11] iommu/sva: Add iommu_domain type for SVA

[Lu Baolu <baolu.lu@linux.intel.com>]

On 2022/3/30 5:38, Jacob Pan wrote:
>> +static struct iommu_domain *
>> +iommu_sva_alloc_domain(struct device *dev, struct mm_struct *mm)
>> +{
>> +	struct bus_type *bus = dev->bus;
>> +	struct iommu_sva_cookie *cookie;
>> +	struct iommu_domain *domain;
>> +	void *curr;
>> +
>> +	if (!bus || !bus->iommu_ops)
>> +		return NULL;
>> +
>> +	cookie = kzalloc(sizeof(*cookie), GFP_KERNEL);
>> +	if (!cookie)
>> +		return NULL;
>> +
>> +	domain = bus->iommu_ops->domain_alloc(IOMMU_DOMAIN_SVA);
>> +	if (!domain)
>> +		goto err_domain_alloc;
>> +
>> +	cookie->mm = mm;
>> +	cookie->pasid = mm->pasid;
> How do you manage the mm life cycle? do you require caller take mm reference?
> Or this should be limited to the current mm?
> 

The existing sva_bind() interface requires the caller to take the mm
reference before calling it. So mm is safe during sva bind() and
unbind().

drivers/iommu/iommu.c:
/**
  * iommu_sva_bind_device() - Bind a process address space to a device
  * @dev: the device
  * @mm: the mm to bind, caller must hold a reference to it
  * @drvdata: opaque data pointer to pass to bind callback
  *
  * Create a bond between device and address space, allowing the device 
to access
  * the mm using the returned PASID. If a bond already exists between 
@device and
  * @mm, it is returned and an additional reference is taken. Caller 
must call
  * iommu_sva_unbind_device() to release each reference.
  *
  * iommu_dev_enable_feature(dev, IOMMU_DEV_FEAT_SVA) must be called 
first, to
  * initialize the required SVA features.
  *
  * On error, returns an ERR_PTR value.
  */
struct iommu_sva *
iommu_sva_bind_device(struct device *dev, struct mm_struct *mm, void 
*drvdata)

Best regards,
baolu