[RFC PATCH] iommu: create direct_mapping after device attached

[RFC PATCH] iommu: create direct_mapping after device attached

[honghui.zhang at mediatek.com]

From: Honghui Zhang <honghui.zhang@mediatek.com>

For mtk iommu, the domain_finalize was called in device attatch, the mtk
iommu iopgt ops was allocated and initialized in domain_finalize, the
iommu_group_create_direct_mappings would call the map interface to
implement the map. If it's earlier than device attach, there would be NULL
dereference. Move the iommu_group_create_direct_mappings call after device
attached.

Signed-off-by: Honghui Zhang <honghui.zhang@mediatek.com>
---
 drivers/iommu/iommu.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 3000051..24c671c 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -427,14 +427,19 @@ rename:
 
 	dev->iommu_group = group;
 
-	iommu_group_create_direct_mappings(group, dev);
-
 	mutex_lock(&group->mutex);
 	list_add_tail(&device->list, &group->devices);
 	if (group->domain)
 		__iommu_attach_device(group->domain, dev);
 	mutex_unlock(&group->mutex);
 
+	/*
+	 * For some iommu driver like mtk iommu, the map callback was assigned
+	 * after device attached. The direct_mappings would call iommu map and
+	 * dereference NULL if it's called earlier than attach_device.
+	 */
+	iommu_group_create_direct_mappings(group, dev);
+
 	/* Notify any listeners about change to group. */
 	blocking_notifier_call_chain(&group->notifier,
 				     IOMMU_GROUP_NOTIFY_ADD_DEVICE, dev);
-- 
1.8.1.1.dirty

[RFC PATCH] iommu: create direct_mapping after device attached

[Joerg Roedel]

On Wed, Jul 20, 2016 at 08:49:21PM +0800, honghui.zhang at mediatek.com wrote:
> From: Honghui Zhang <honghui.zhang@mediatek.com>
> 
> For mtk iommu, the domain_finalize was called in device attatch, the mtk
> iommu iopgt ops was allocated and initialized in domain_finalize, the
> iommu_group_create_direct_mappings would call the map interface to
> implement the map. If it's earlier than device attach, there would be NULL
> dereference. Move the iommu_group_create_direct_mappings call after device
> attached.

No, this would open a race window where the device is attached, but
doesn't have its unity-mappings in place. You should re-organize the mtk
driver instead, so that it works in this order too.



	Joerg