[PATCH v8 18/29] iommu/smmuv3: Nested mode single MSI doorbell per domain enforcement

[Eric Auger]

In nested mode we enforce the rule that all devices belonging
to the same iommu_domain share the same msi_domain.

Indeed if there were several physical MSI doorbells being used
within a single iommu_domain, it becomes really difficult to
resolve the nested stage mapping translating into the correct
physical doorbell. So let's forbid this situation.

Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx>
---
 drivers/iommu/arm-smmu-v3.c | 41 +++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index b4813f23f302..31d8028bb997 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -2048,6 +2048,37 @@ static void arm_smmu_detach_dev(struct arm_smmu_master *master)
 	arm_smmu_disable_ats(master);
 }
 
+static bool arm_smmu_share_msi_domain(struct iommu_domain *domain,
+				      struct device *dev)
+{
+	struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
+	struct irq_domain *irqd = dev_get_msi_domain(dev);
+	struct arm_smmu_master *master;
+	unsigned long flags;
+	bool share = false;
+
+	if (!irqd)
+		return true;
+
+	spin_lock_irqsave(&smmu_domain->devices_lock, flags);
+	list_for_each_entry(master, &smmu_domain->devices, domain_head) {
+		struct irq_domain *d = dev_get_msi_domain(master->dev);
+
+		if (!d)
+			continue;
+		if (irqd != d) {
+			dev_info(dev, "Nested mode forbids to attach devices "
+				 "using different physical MSI doorbells "
+				 "to the same iommu_domain");
+			goto unlock;
+		}
+	}
+	share = true;
+unlock:
+	spin_unlock_irqrestore(&smmu_domain->devices_lock, flags);
+	return share;
+}
+
 static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
 {
 	int ret = 0;
@@ -2082,6 +2113,16 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
 		ret = -ENXIO;
 		goto out_unlock;
 	}
+	/*
+	 * In nested mode we must check all devices belonging to the
+	 * domain share the same physical MSI doorbell. Otherwise nested
+	 * stage MSI binding is not supported.
+	 */
+	if (smmu_domain->stage == ARM_SMMU_DOMAIN_NESTED &&
+		!arm_smmu_share_msi_domain(domain, dev)) {
+		ret = -EINVAL;
+		goto out_unlock;
+	}
 
 	master->domain = smmu_domain;
 
-- 
2.20.1