[PATCH 12/12] iommu/arm-smmu: Group platform devices appropriately

[Robin Murphy]

IOMMU groups are necessary to represent multiple devices which the IOMMU
cannot tell apart; if two platform devices are wired up with the same
stream ID, then the current approach of blindly placing every device in
its own group makes it possible for each device to end up attached to a
different domain. This is a Very Bad Thing under the SMMU architecture,
where mapping a stream ID to more than one context leads to various
unpleasant behaviours.

In the absence of a suitable common abstraction (which is difficult due
to the implementation-specific nature of platform device IDs), implement
a simple lookup table within the SMMU driver to ensure that any devices
with overlapping stream IDs end up in the same group as they should.

Signed-off-by: Robin Murphy <robin.murphy at arm.com>
---
 drivers/iommu/arm-smmu.c | 61 +++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 50 insertions(+), 11 deletions(-)

diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
index 8fcf27a..2d65de4 100644
--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -333,6 +333,7 @@ struct arm_smmu_device {
 
 	u32				num_mapping_groups;
 	DECLARE_BITMAP(smr_map, ARM_SMMU_MAX_SMRS);
+	struct iommu_group		**group_lut;
 
 	unsigned long			va_size;
 	unsigned long			ipa_size;
@@ -1272,11 +1273,6 @@ static int arm_smmu_add_device(struct device *dev)
 			return ret;
 	}
 
-	/*
-	 * For now, assume that the default group allocators suffice.
-	 * We might have to do some preparatory work here to properly
-	 * handle multiple devices sharing stream IDs.
-	 */
 	group = iommu_group_get_for_dev(dev);
 	if (IS_ERR(group))
 		return PTR_ERR(group);
@@ -1297,6 +1293,45 @@ static void __arm_smmu_release_iommudata(void *data)
 	kfree(data);
 }
 
+static struct iommu_group *arm_smmu_group_lookup(struct device *dev)
+{
+	struct arm_smmu_master_cfg *cfg = dev->archdata.iommu;
+	struct arm_smmu_device *smmu = cfg->smmu;
+	struct iommu_group **lut = smmu->group_lut;
+	struct iommu_group *group = NULL;
+	int i;
+
+	if (!lut) {
+		/*
+		 * Unfortunately this has to be sized for the worst-case until
+		 * we get even cleverer with stream ID management.
+		 */
+		lut = devm_kcalloc(smmu->dev, SMR_ID_MASK + 1,
+				   sizeof(*lut), GFP_KERNEL);
+		if (lut)
+			smmu->group_lut = lut;
+		else
+			group = ERR_PTR(-ENOMEM);
+	} else {
+		/* Check for platform or cross-bus aliases */
+		for (i = 0; i < cfg->num_streamids; i++) {
+			struct iommu_group *tmp = lut[cfg->streamids[i].id];
+
+			if (!tmp)
+				continue;
+
+			if (group && tmp != group) {
+				dev_err(smmu->dev,
+					"Cannot handle master %s aliasing multiple groups\n",
+					dev_name(dev));
+				return ERR_PTR(-EBUSY);
+			}
+			group = tmp;
+		}
+	}
+	return group;
+}
+
 static inline bool __streamid_match_sme(struct arm_smmu_streamid *sid,
 					struct arm_smmu_stream_map_entry *sme)
 {
@@ -1306,22 +1341,24 @@ static inline bool __streamid_match_sme(struct arm_smmu_streamid *sid,
 
 static struct iommu_group *arm_smmu_device_group(struct device *dev)
 {
-	struct arm_smmu_master_cfg *master_cfg;
+	struct arm_smmu_master_cfg *master_cfg = dev->archdata.iommu;
 	struct arm_smmu_group_cfg *group_cfg;
 	struct arm_smmu_streamid *sids;
 	struct arm_smmu_stream_map_entry *smes;
 	struct iommu_group *group;
 	int i, j;
 
-	if (dev_is_pci(dev))
-		group = pci_device_group(dev);
-	else
-		group = generic_device_group(dev);
+	group = arm_smmu_group_lookup(dev);
+	if (!group) {
+		if (dev_is_pci(dev))
+			group = pci_device_group(dev);
+		else
+			group = generic_device_group(dev);
+	}
 
 	if (IS_ERR(group))
 		return group;
 
-	master_cfg = dev->archdata.iommu;
 	group_cfg = iommu_group_get_iommudata(group);
 	if (!group_cfg) {
 		group_cfg = kzalloc(sizeof(*group_cfg), GFP_KERNEL);
@@ -1336,6 +1373,8 @@ static struct iommu_group *arm_smmu_device_group(struct device *dev)
 	sids = master_cfg->streamids;
 	smes = group_cfg->smes;
 	for (i = 0; i < master_cfg->num_streamids; i++) {
+		master_cfg->smmu->group_lut[sids[i].id] = group;
+
 		for (j = 0; j < group_cfg->num_smes; j++) {
 			if (__streamid_match_sme(&sids[i], &smes[j])) {
 				sids[i].s2cr_idx = STREAM_MULTIPLE;
-- 
2.7.2.333.g70bd996.dirty