iommu/dart: Fix apple_dart_device_group for PCI groups

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: f0b6368 ("iommu/dart: Clear sid2group entry when a group is freed")
Signed-off-by: Sven Peter <[email protected]>
Reviewed-by: Eric Curtin <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Joerg Roedel <[email protected]>

Author: svenpeter42

drivers/iommu/apple-dart.c

@@ -835,6 +835,29 @@ 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;
@@ -876,14 +899,28 @@ 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)