[PATCH] iommu/dart: Fix apple_dart_device_group for PCI groups

[Sven Peter <sven@svenpeter.dev>]

pci_device_group() can return an already existing IOMMU group if the PCI
device's pagetables have to be shared with another one due to bus
toplogy, isolation features and/or DMA alias quirks.
apple_dart_device_group() however assumes that the group has just been
created and overwrites its iommudata which will eventually lead to
apple_dart_release_group leaving stale entries in sid2group.
Fix that by merging the iommudata if the returned group already exists.

Fixes: f0b636804c7c ("iommu/dart: Clear sid2group entry when a group is freed")
Signed-off-by: Sven Peter <sven@svenpeter.dev>
---
 drivers/iommu/apple-dart.c | 51 ++++++++++++++++++++++++++++++++------
 1 file changed, 44 insertions(+), 7 deletions(-)

This won't apply cleanly to iommu/fixes as it's based on the t8110 DART
changes since the USB4/Thunderbolt DART itself also depends on those.
That's not a big deal though since it's not possible to run into this
bug without complex PCI bus topologies which can only be created using
USB4/Thunderbolt on these SoCs and there's no support for that upstream
yet.

diff --git a/drivers/iommu/apple-dart.c b/drivers/iommu/apple-dart.c
index a1304ba3639b..02f7a1740b14 100644
--- a/drivers/iommu/apple-dart.c
+++ b/drivers/iommu/apple-dart.c
@@ -840,6 +840,29 @@ static void apple_dart_release_group(void *iommu_data)
 	mutex_unlock(&apple_dart_groups_lock);
 }
 
+static int apple_dart_merge_master_cfg(struct apple_dart_master_cfg *dst,
+				       struct apple_dart_master_cfg *src)
+{
+	/*
+	 * We know that this function is only called for groups returned from
+	 * pci_device_group and that all Apple Silicon platforms never spread
+	 * PCIe devices from the same bus across multiple DARTs such that we can
+	 * just assume that both src and dst only have the same single DART.
+	 */
+	if (src->stream_maps[1].dart)
+		return -EINVAL;
+	if (dst->stream_maps[1].dart)
+		return -EINVAL;
+	if (src->stream_maps[0].dart != dst->stream_maps[0].dart)
+		return -EINVAL;
+
+	bitmap_or(dst->stream_maps[0].sidmap,
+		  dst->stream_maps[0].sidmap,
+		  src->stream_maps[0].sidmap,
+		  dst->stream_maps[0].dart->num_streams);
+	return 0;
+}
+
 static struct iommu_group *apple_dart_device_group(struct device *dev)
 {
 	int i, sid;
@@ -881,14 +904,28 @@ static struct iommu_group *apple_dart_device_group(struct device *dev)
 	if (!group)
 		goto out;
 
-	group_master_cfg = kmemdup(cfg, sizeof(*group_master_cfg), GFP_KERNEL);
-	if (!group_master_cfg) {
-		iommu_group_put(group);
-		goto out;
-	}
+	group_master_cfg = iommu_group_get_iommudata(group);
+	if (group_master_cfg) {
+		int ret;
 
-	iommu_group_set_iommudata(group, group_master_cfg,
-		apple_dart_release_group);
+		ret = apple_dart_merge_master_cfg(group_master_cfg, cfg);
+		if (ret) {
+			dev_err(dev, "Failed to merge DART IOMMU grups.\n");
+			iommu_group_put(group);
+			res = ERR_PTR(ret);
+			goto out;
+		}
+	} else {
+		group_master_cfg = kmemdup(cfg, sizeof(*group_master_cfg),
+					   GFP_KERNEL);
+		if (!group_master_cfg) {
+			iommu_group_put(group);
+			goto out;
+		}
+
+		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, stream_map->dart->num_streams)
-- 
2.25.1