iommu/vt-d: Fix possible recursive locking in intel_iommu_init()

The global rwsem dmar_global_lock was introduced by commit 3a5670e8ac932
("iommu/vt-d: Introduce a rwsem to protect global data structures"). It
is used to protect DMAR related global data from DMAR hotplug operations.

The dmar_global_lock used in the intel_iommu_init() might cause recursive
locking issue, for example, intel_iommu_get_resv_regions() is taking the
dmar_global_lock from within a section where intel_iommu_init() already
holds it via probe_acpi_namespace_devices().

Using dmar_global_lock in intel_iommu_init() could be relaxed since it is
unlikely that any IO board must be hot added before the IOMMU subsystem is
initialized. This eliminates the possible recursive locking issue by moving
down DMAR hotplug support after the IOMMU is initialized and removing the
uses of dmar_global_lock in intel_iommu_init().

Fixes: d5692d4af08cd ("iommu/vt-d: Fix suspicious RCU usage in probe_acpi_namespace_devices()")
Reported-by: Robin Murphy <[e-mail]>
Signed-off-by: Lu Baolu <[e-mail]>
Reviewed-by: Kevin Tian <[e-mail]>
Link: https://lore.kernel.org/r/894d[e-mail]
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Joerg Roedel <[e-mail]>

drivers/iommu/intel/dmar.c

···
 	if (!dmar_in_use())
 		return 0;
 
+	/*
+	 * It's unlikely that any I/O board is hot added before the IOMMU
+	 * subsystem is initialized.
+	 */
+	if (IS_ENABLED(CONFIG_INTEL_IOMMU) && !intel_iommu_enabled)
+		return -EOPNOTSUPP;
+
 	if (dmar_detect_dsm(handle, DMAR_DSM_FUNC_DRHD)) {
 		tmp = handle;
 	} else {

drivers/iommu/intel/iommu.c

···
 
 #ifdef CONFIG_INTEL_IOMMU_SVM
 		if (pasid_supported(iommu) && ecap_prs(iommu->ecap)) {
-			/*
-			 * Call dmar_alloc_hwirq() with dmar_global_lock held,
-			 * could cause possible lock race condition.
-			 */
-			up_write(&dmar_global_lock);
 			ret = intel_svm_enable_prq(iommu);
-			down_write(&dmar_global_lock);
 			if (ret)
 				goto free_iommu;
 		}
···
 	force_on = (!intel_iommu_tboot_noforce && tboot_force_iommu()) ||
 		    platform_optin_force_iommu();
 
-	down_write(&dmar_global_lock);
 	if (dmar_table_init()) {
 		if (force_on)
 			panic("tboot: Failed to initialize DMAR table\n");
···
 			panic("tboot: Failed to initialize DMAR device scope\n");
 		goto out_free_dmar;
 	}
-
-	up_write(&dmar_global_lock);
-
-	/*
-	 * The bus notifier takes the dmar_global_lock, so lockdep will
-	 * complain later when we register it under the lock.
-	 */
-	dmar_register_bus_notifier();
-
-	down_write(&dmar_global_lock);
 
 	if (!no_iommu)
 		intel_iommu_debugfs_init();
···
 		pr_err("Initialization failed\n");
 		goto out_free_dmar;
 	}
-	up_write(&dmar_global_lock);
 
 	init_iommu_pm_ops();
 
-	down_read(&dmar_global_lock);
 	for_each_active_iommu(iommu, drhd) {
 		/*
 		 * The flush queue implementation does not perform
···
 				       "%s", iommu->name);
 		iommu_device_register(&iommu->iommu, &intel_iommu_ops, NULL);
 	}
-	up_read(&dmar_global_lock);
 
 	bus_set_iommu(&pci_bus_type, &intel_iommu_ops);
 	if (si_domain && !hw_pass_through)
 		register_memory_notifier(&intel_iommu_memory_nb);
 
-	down_read(&dmar_global_lock);
 	if (probe_acpi_namespace_devices())
 		pr_warn("ACPI name space devices didn't probe correctly\n");
 
···
 
 		iommu_disable_protect_mem_regions(iommu);
 	}
-	up_read(&dmar_global_lock);
-
-	pr_info("Intel(R) Virtualization Technology for Directed I/O\n");
 
 	intel_iommu_enabled = 1;
+	dmar_register_bus_notifier();
+	pr_info("Intel(R) Virtualization Technology for Directed I/O\n");
 
 	return 0;
 
 out_free_dmar:
 	intel_iommu_free_dmars();
-	up_write(&dmar_global_lock);
 	return ret;
 }
 

include/linux/dmar.h

···
 
 extern struct rw_semaphore dmar_global_lock;
 extern struct list_head dmar_drhd_units;
+extern int intel_iommu_enabled;
 
 #define for_each_drhd_unit(drhd)					\
 	list_for_each_entry_rcu(drhd, &dmar_drhd_units, list,		\
···
 static inline bool dmar_rcu_check(void)
 {
 	return rwsem_is_locked(&dmar_global_lock) ||
-	       system_state == SYSTEM_BOOTING;
+	       system_state == SYSTEM_BOOTING ||
+	       (IS_ENABLED(CONFIG_INTEL_IOMMU) && !intel_iommu_enabled);
 }
 
 #define	dmar_rcu_dereference(p)	rcu_dereference_check((p), dmar_rcu_check())