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SubjectRe: [PATCH v6 08/12] iommu/sva: Use attach/detach_pasid_dev in SVA interfaces
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On 2022/5/10 23:23, Jason Gunthorpe wrote:
> On Tue, May 10, 2022 at 02:17:34PM +0800, Lu Baolu wrote:
>
>> +/**
>> + * 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 mm_users
>> + * @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)
>> +{
>> + int ret = -EINVAL;
>> + struct iommu_sva *handle;
>> + struct iommu_domain *domain;
>> +
>> + /*
>> + * TODO: Remove the drvdata parameter after kernel PASID support is
>> + * enabled for the idxd driver.
>> + */
>> + if (drvdata)
>> + return ERR_PTR(-EOPNOTSUPP);
>
> Why is this being left behind? Clean up the callers too please.

Okay, let me try to.

>
>> + /* Allocate mm->pasid if necessary. */
>> + ret = iommu_sva_alloc_pasid(mm, 1, (1U << dev->iommu->pasid_bits) - 1);
>> + if (ret)
>> + return ERR_PTR(ret);
>> +
>> + mutex_lock(&iommu_sva_lock);
>> + /* Search for an existing bond. */
>> + handle = xa_load(&dev->iommu->sva_bonds, mm->pasid);
>> + if (handle) {
>> + refcount_inc(&handle->users);
>> + goto out_success;
>> + }
>
> How can there be an existing bond?
>
> dev->iommu is per-device
>
> The device_group_immutable_singleton() insists on a single device
> group
>
> Basically 'sva_bonds' is the same thing as the group->pasid_array.

Yes, really.

>
> Assuming we leave room for multi-device groups this logic should just
> be
>
> group = iommu_group_get(dev);
> if (!group)
> return -ENODEV;
>
> mutex_lock(&group->mutex);
> domain = xa_load(&group->pasid_array, mm->pasid);
> if (!domain || domain->type != IOMMU_DOMAIN_SVA || domain->mm != mm)
> domain = iommu_sva_alloc_domain(dev, mm);
>
> ?

Agreed. As a helper in iommu core, how about making it more generic like
below?

+struct iommu_domain *iommu_get_domain_for_dev_pasid(struct device *dev,
+ iosid_t pasid,
+ unsigned int type)
+{
+ struct iommu_domain *domain;
+ struct iommu_group *group;
+
+ if (!pasid_valid(pasid))
+ return NULL;
+
+ group = iommu_group_get(dev);
+ if (!group)
+ return NULL;
+
+ mutex_lock(&group->mutex);
+ domain = xa_load(&group->pasid_array, pasid);
+ if (domain && domain->type != type)
+ domain = NULL;
+ mutex_unlock(&group->mutex);
+ iommu_group_put(group);
+
+ return domain;
+}

>
> And stick the refcount in the sva_domain
>
> Also, given the current arrangement it might make sense to have a
> struct iommu_domain_sva given that no driver is wrappering this in
> something else.

Fair enough. How about below wrapper?

+struct iommu_sva_domain {
+ /*
+ * Common iommu domain header, *must* be put at the top
+ * of the structure.
+ */
+ struct iommu_domain domain;
+ struct mm_struct *mm;
+ struct iommu_sva bond;
+}

The refcount is wrapped in bond.

Best regards,
baolu

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