[PATCH] iommu/dart: Clear sid2group entry when a group is freed

[Sven Peter <sven@svenpeter.dev>]

sid2groups keeps track of which stream id combinations belong to a
iommu_group to assign those correctly to devices.
When a iommu_group is freed a stale pointer will however remain in
sid2groups. This prevents devices with the same stream id combination
to ever be attached again (see below).
Fix that by creating a shadow copy of the stream id configuration
when a group is allocated for the first time and clear the sid2group
entry when that group is freed.

  # echo 1 >/sys/bus/pci/devices/0000\:03\:00.0/remove
  pci 0000:03:00.0: Removing from iommu group 1
  # echo 1 >/sys/bus/pci/rescan
  [...]
  pci 0000:03:00.0: BAR 0: assigned [mem 0x6a0000000-0x6a000ffff 64bit pref]
  pci 0000:03:00.0: BAR 2: assigned [mem 0x6a0010000-0x6a001ffff 64bit pref]
  pci 0000:03:00.0: BAR 6: assigned [mem 0x6c0100000-0x6c01007ff pref]
  tg3 0000:03:00.0: Failed to add to iommu group 1: -2
  [...]

Fixes: 46d1fb072e76b161 ("iommu/dart: Add DART iommu driver")
Reported-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Sven Peter <sven@svenpeter.dev>
---
 drivers/iommu/apple-dart.c | 38 +++++++++++++++++++++++++++++++++++---
 1 file changed, 35 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/apple-dart.c b/drivers/iommu/apple-dart.c
index 47ffe9e49abb..f82b2c46493a 100644
--- a/drivers/iommu/apple-dart.c
+++ b/drivers/iommu/apple-dart.c
@@ -636,16 +636,34 @@ static int apple_dart_of_xlate(struct device *dev, struct of_phandle_args *args)
 	return -EINVAL;
 }
 
+static DEFINE_MUTEX(apple_dart_groups_lock);
+
+static void apple_dart_release_group(void *iommu_data)
+{
+	int i, sid;
+	struct apple_dart_stream_map *stream_map;
+	struct apple_dart_master_cfg *group_master_cfg = iommu_data;
+
+	mutex_lock(&apple_dart_groups_lock);
+
+	for_each_stream_map(i, group_master_cfg, stream_map)
+		for_each_set_bit(sid, &stream_map->sidmap, DART_MAX_STREAMS)
+			stream_map->dart->sid2group[sid] = NULL;
+
+	kfree(iommu_data);
+	mutex_unlock(&apple_dart_groups_lock);
+}
+
 static struct iommu_group *apple_dart_device_group(struct device *dev)
 {
-	static DEFINE_MUTEX(lock);
 	int i, sid;
 	struct apple_dart_master_cfg *cfg = dev_iommu_priv_get(dev);
 	struct apple_dart_stream_map *stream_map;
+	struct apple_dart_master_cfg *group_master_cfg;
 	struct iommu_group *group = NULL;
 	struct iommu_group *res = ERR_PTR(-EINVAL);
 
-	mutex_lock(&lock);
+	mutex_lock(&apple_dart_groups_lock);
 
 	for_each_stream_map(i, cfg, stream_map) {
 		for_each_set_bit(sid, &stream_map->sidmap, DART_MAX_STREAMS) {
@@ -673,6 +691,20 @@ static struct iommu_group *apple_dart_device_group(struct device *dev)
 #endif
 		group = generic_device_group(dev);
 
+	res = ERR_PTR(-ENOMEM);
+	if (!group)
+		goto out;
+
+	group_master_cfg = kzalloc(sizeof(*group_master_cfg), GFP_KERNEL);
+	if (!group_master_cfg) {
+		iommu_group_put(group);
+		goto out;
+	}
+
+	memcpy(group_master_cfg, cfg, sizeof(*group_master_cfg));
+	iommu_group_set_iommudata(group, group_master_cfg,
+		apple_dart_release_group);
+
 	for_each_stream_map(i, cfg, stream_map)
 		for_each_set_bit(sid, &stream_map->sidmap, DART_MAX_STREAMS)
 			stream_map->dart->sid2group[sid] = group;
@@ -680,7 +712,7 @@ static struct iommu_group *apple_dart_device_group(struct device *dev)
 	res = group;
 
 out:
-	mutex_unlock(&lock);
+	mutex_unlock(&apple_dart_groups_lock);
 	return res;
 }
 
-- 
2.25.1