iommu/vt-d: Introduce a rwsem to protect global data structures

Introduce a global rwsem dmar_global_lock, which will be used to
protect DMAR related global data structures from DMAR/PCI/memory
device hotplug operations in process context.

DMA and interrupt remapping related data structures are read most,
and only change when memory/PCI/DMAR hotplug event happens.
So a global rwsem solution is adopted for balance between simplicity
and performance.

For interrupt remapping driver, function intel_irq_remapping_supported(),
dmar_table_init(), intel_enable_irq_remapping(), disable_irq_remapping(),
reenable_irq_remapping() and enable_drhd_fault_handling() etc
are called during booting, suspending and resuming with interrupt
disabled, so no need to take the global lock.

For interrupt remapping entry allocation, the locking model is:
	down_read(&dmar_global_lock);
	/* Find corresponding iommu */
	iommu = map_hpet_to_ir(id);
	if (iommu)
		/*
		 * Allocate remapping entry and mark entry busy,
		 * the IOMMU won't be hot-removed until the
		 * allocated entry has been released.
		 */
		index = alloc_irte(iommu, irq, 1);
	up_read(&dmar_global_lock);

For DMA remmaping driver, we only uses the dmar_global_lock rwsem to
protect functions which are only called in process context. For any
function which may be called in interrupt context, we will use RCU
to protect them in following patches.

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Signed-off-by: Joerg Roedel <joro@8bytes.org>

1 files changed, 13 insertions, 9 deletions

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index bb98e37f2cf7..50d639a2df88 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -3637,11 +3637,13 @@ static int device_notifier(struct notifier_block *nb,
         if (!domain)
                 return 0;
 
+        down_read(&dmar_global_lock);
         domain_remove_one_dev_info(domain, pdev);
         if (!(domain->flags & DOMAIN_FLAG_VIRTUAL_MACHINE) &&
             !(domain->flags & DOMAIN_FLAG_STATIC_IDENTITY) &&
             list_empty(&domain->devices))
                 domain_exit(domain);
+        up_read(&dmar_global_lock);
 
         return 0;
 }
@@ -3659,6 +3661,13 @@ int __init intel_iommu_init(void)
         /* VT-d is required for a TXT/tboot launch, so enforce that */
         force_on = tboot_force_iommu();
 
+        if (iommu_init_mempool()) {
+                if (force_on)
+                        panic("tboot: Failed to initialize iommu memory\n");
+                return -ENOMEM;
+        }
+
+        down_write(&dmar_global_lock);
         if (dmar_table_init()) {
                 if (force_on)
                         panic("tboot: Failed to initialize DMAR table\n");
@@ -3681,12 +3690,6 @@ int __init intel_iommu_init(void)
         if (no_iommu || dmar_disabled)
                 goto out_free_dmar;
 
-        if (iommu_init_mempool()) {
-                if (force_on)
-                        panic("tboot: Failed to initialize iommu memory\n");
-                goto out_free_dmar;
-        }
-
         if (list_empty(&dmar_rmrr_units))
                 printk(KERN_INFO "DMAR: No RMRR found\n");
 
@@ -3696,7 +3699,7 @@ int __init intel_iommu_init(void)
         if (dmar_init_reserved_ranges()) {
                 if (force_on)
                         panic("tboot: Failed to reserve iommu ranges\n");
-                goto out_free_mempool;
+                goto out_free_reserved_range;
         }
 
         init_no_remapping_devices();
@@ -3708,6 +3711,7 @@ int __init intel_iommu_init(void)
                 printk(KERN_ERR "IOMMU: dmar init failed\n");
                 goto out_free_reserved_range;
         }
+        up_write(&dmar_global_lock);
         printk(KERN_INFO
         "PCI-DMA: Intel(R) Virtualization Technology for Directed I/O\n");
 
@@ -3729,10 +3733,10 @@ int __init intel_iommu_init(void)
 
 out_free_reserved_range:
         put_iova_domain(&reserved_iova_list);
-out_free_mempool:
-        iommu_exit_mempool();
 out_free_dmar:
         intel_iommu_free_dmars();
+        up_write(&dmar_global_lock);
+        iommu_exit_mempool();
         return ret;
 }