iommu/vt-d: Remove clearing translation data in disable_dmar_iommu()

The disable_dmar_iommu() is called when IOMMU initialization fails or
the IOMMU is hot-removed from the system. In both cases, there is no
need to clear the IOMMU translation data structures for devices.

On the initialization path, the device probing only happens after the
IOMMU is initialized successfully, hence there're no translation data
structures.

On the hot-remove path, there is no real use case where the IOMMU is
hot-removed, but the devices that it manages are still alive in the
system. The translation data structures were torn down during device
release, hence there's no need to repeat it in IOMMU hot-remove path
either. This removes the unnecessary code and only leaves a check.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Link: https://lore.kernel.org/r/20220706025524.2904370-3-baolu.lu@linux.intel.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/intel/iommu.c

@@ -1716,23 +1716,16 @@ static int iommu_init_domains(struct intel_iommu *iommu)
 
 static void disable_dmar_iommu(struct intel_iommu *iommu)
 {
-	struct device_domain_info *info, *tmp;
-	unsigned long flags;
-
 	if (!iommu->domain_ids)
 		return;
 
-	spin_lock_irqsave(&device_domain_lock, flags);
-	list_for_each_entry_safe(info, tmp, &device_domain_list, global) {
-		if (info->iommu != iommu)
-			continue;
-
-		if (!info->dev || !info->domain)
-			continue;
-
-		__dmar_remove_one_dev_info(info);
-	}
-	spin_unlock_irqrestore(&device_domain_lock, flags);
+	/*
+	 * All iommu domains must have been detached from the devices,
+	 * hence there should be no domain IDs in use.
+	 */
+	if (WARN_ON(bitmap_weight(iommu->domain_ids, cap_ndoms(iommu->cap))
+		    > NUM_RESERVED_DID))
+		return;
 
 	if (iommu->gcmd & DMA_GCMD_TE)
 		iommu_disable_translation(iommu);

drivers/iommu/intel/pasid.h

@@ -39,6 +39,7 @@
  * only and pass-through transfer modes.
  */
 #define FLPT_DEFAULT_DID		1
+#define NUM_RESERVED_DID		2
 
 /*
  * The SUPERVISOR_MODE flag indicates a first level translation which