iommu: Introduce domain attachment handle

Currently, when attaching a domain to a device or its PASID, domain is
stored within the iommu group. It could be retrieved for use during the
window between attachment and detachment.

With new features introduced, there's a need to store more information
than just a domain pointer. This information essentially represents the
association between a domain and a device. For example, the SVA code
already has a custom struct iommu_sva which represents a bond between
sva domain and a PASID of a device. Looking forward, the IOMMUFD needs
a place to store the iommufd_device pointer in the core, so that the
device object ID could be quickly retrieved in the critical fault handling
path.

Introduce domain attachment handle that explicitly represents the
attachment relationship between a domain and a device or its PASID.

Co-developed-by: Jason Gunthorpe <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]>
Signed-off-by: Lu Baolu <[email protected]>
Reviewed-by: Jason Gunthorpe <[email protected]>
Reviewed-by: Kevin Tian <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Will Deacon <[email protected]>

Author: LuBaolu

drivers/dma/idxd/init.c

@@ -584,7 +584,7 @@ static int idxd_enable_system_pasid(struct idxd_device *idxd)
 	 * DMA domain is owned by the driver, it should support all valid
 	 * types such as DMA-FQ, identity, etc.
 	 */
-	ret = iommu_attach_device_pasid(domain, dev, pasid);
+	ret = iommu_attach_device_pasid(domain, dev, pasid, NULL);
 	if (ret) {
 		dev_err(dev, "failed to attach device pasid %d, domain type %d",
 			pasid, domain->type);

drivers/iommu/iommu-sva.c

@@ -99,7 +99,9 @@ struct iommu_sva *iommu_sva_bind_device(struct device *dev, struct mm_struct *mm
 
 	/* Search for an existing domain. */
 	list_for_each_entry(domain, &mm->iommu_mm->sva_domains, next) {
-		ret = iommu_attach_device_pasid(domain, dev, iommu_mm->pasid);
+		handle->handle.domain = domain;
+		ret = iommu_attach_device_pasid(domain, dev, iommu_mm->pasid,
+						&handle->handle);
 		if (!ret) {
 			domain->users++;
 			goto out;
@@ -113,7 +115,9 @@ struct iommu_sva *iommu_sva_bind_device(struct device *dev, struct mm_struct *mm
 		goto out_free_handle;
 	}
 
-	ret = iommu_attach_device_pasid(domain, dev, iommu_mm->pasid);
+	handle->handle.domain = domain;
+	ret = iommu_attach_device_pasid(domain, dev, iommu_mm->pasid,
+					&handle->handle);
 	if (ret)
 		goto out_free_domain;
 	domain->users = 1;
@@ -124,7 +128,6 @@ struct iommu_sva *iommu_sva_bind_device(struct device *dev, struct mm_struct *mm
 	list_add(&handle->handle_item, &mm->iommu_mm->sva_handles);
 	mutex_unlock(&iommu_sva_lock);
 	handle->dev = dev;
-	handle->domain = domain;
 	return handle;
 
 out_free_domain:
@@ -147,7 +150,7 @@ EXPORT_SYMBOL_GPL(iommu_sva_bind_device);
  */
 void iommu_sva_unbind_device(struct iommu_sva *handle)
 {
-	struct iommu_domain *domain = handle->domain;
+	struct iommu_domain *domain = handle->handle.domain;
 	struct iommu_mm_data *iommu_mm = domain->mm->iommu_mm;
 	struct device *dev = handle->dev;
 
@@ -170,7 +173,7 @@ EXPORT_SYMBOL_GPL(iommu_sva_unbind_device);
 
 u32 iommu_sva_get_pasid(struct iommu_sva *handle)
 {
-	struct iommu_domain *domain = handle->domain;
+	struct iommu_domain *domain = handle->handle.domain;
 
 	return mm_get_enqcmd_pasid(domain->mm);
 }

drivers/iommu/iommu.c

@@ -3352,16 +3352,17 @@ static void __iommu_remove_group_pasid(struct iommu_group *group,
  * @domain: the iommu domain.
  * @dev: the attached device.
  * @pasid: the pasid of the device.
+ * @handle: the attach handle.
  *
  * Return: 0 on success, or an error.
  */
 int iommu_attach_device_pasid(struct iommu_domain *domain,
-			      struct device *dev, ioasid_t pasid)
+			      struct device *dev, ioasid_t pasid,
+			      struct iommu_attach_handle *handle)
 {
 	/* Caller must be a probed driver on dev */
 	struct iommu_group *group = dev->iommu_group;
 	struct group_device *device;
-	void *curr;
 	int ret;
 
 	if (!domain->ops->set_dev_pasid)
@@ -3382,11 +3383,12 @@ int iommu_attach_device_pasid(struct iommu_domain *domain,
 		}
 	}
 
-	curr = xa_cmpxchg(&group->pasid_array, pasid, NULL, domain, GFP_KERNEL);
-	if (curr) {
-		ret = xa_err(curr) ? : -EBUSY;
+	if (handle)
+		handle->domain = domain;
+
+	ret = xa_insert(&group->pasid_array, pasid, handle, GFP_KERNEL);
+	if (ret)
 		goto out_unlock;
-	}
 
 	ret = __iommu_set_group_pasid(domain, group, pasid);
 	if (ret)
@@ -3414,7 +3416,7 @@ void iommu_detach_device_pasid(struct iommu_domain *domain, struct device *dev,
 
 	mutex_lock(&group->mutex);
 	__iommu_remove_group_pasid(group, pasid, domain);
-	WARN_ON(xa_erase(&group->pasid_array, pasid) != domain);
+	xa_erase(&group->pasid_array, pasid);
 	mutex_unlock(&group->mutex);
 }
 EXPORT_SYMBOL_GPL(iommu_detach_device_pasid);
@@ -3439,15 +3441,19 @@ struct iommu_domain *iommu_get_domain_for_dev_pasid(struct device *dev,
 {
 	/* Caller must be a probed driver on dev */
 	struct iommu_group *group = dev->iommu_group;
-	struct iommu_domain *domain;
+	struct iommu_attach_handle *handle;
+	struct iommu_domain *domain = NULL;
 
 	if (!group)
 		return NULL;
 
 	xa_lock(&group->pasid_array);
-	domain = xa_load(&group->pasid_array, pasid);
+	handle = xa_load(&group->pasid_array, pasid);
+	if (handle)
+		domain = handle->domain;
+
 	if (type && domain && domain->type != type)
-		domain = ERR_PTR(-EBUSY);
+		domain = NULL;
 	xa_unlock(&group->pasid_array);
 
 	return domain;

include/linux/iommu.h

@@ -989,12 +989,22 @@ struct iommu_fwspec {
 /* ATS is supported */
 #define IOMMU_FWSPEC_PCI_RC_ATS			(1 << 0)
 
+/*
+ * An iommu attach handle represents a relationship between an iommu domain
+ * and a PASID or RID of a device. It is allocated and managed by the component
+ * that manages the domain and is stored in the iommu group during the time the
+ * domain is attached.
+ */
+struct iommu_attach_handle {
+	struct iommu_domain		*domain;
+};
+
 /**
  * struct iommu_sva - handle to a device-mm bond
  */
 struct iommu_sva {
+	struct iommu_attach_handle	handle;
 	struct device			*dev;
-	struct iommu_domain		*domain;
 	struct list_head		handle_item;
 	refcount_t			users;
 };
@@ -1052,7 +1062,8 @@ int iommu_device_claim_dma_owner(struct device *dev, void *owner);
 void iommu_device_release_dma_owner(struct device *dev);
 
 int iommu_attach_device_pasid(struct iommu_domain *domain,
-			      struct device *dev, ioasid_t pasid);
+			      struct device *dev, ioasid_t pasid,
+			      struct iommu_attach_handle *handle);
 void iommu_detach_device_pasid(struct iommu_domain *domain,
 			       struct device *dev, ioasid_t pasid);
 struct iommu_domain *
@@ -1388,7 +1399,8 @@ static inline int iommu_device_claim_dma_owner(struct device *dev, void *owner)
 }
 
 static inline int iommu_attach_device_pasid(struct iommu_domain *domain,
-					    struct device *dev, ioasid_t pasid)
+					    struct device *dev, ioasid_t pasid,
+					    struct iommu_attach_handle *handle)
 {
 	return -ENODEV;
 }