[PATCH v2 1/3] iommu: Make single-device group for PASID explicit

[Lu Baolu]

The PASID interfaces have always supported only single-device groups.
This was first introduced in commit 26b25a2b98e45 ("iommu: Bind process
address spaces to devices"), and has been kept consistent in subsequent
commits.

However, the core code doesn't explicitly check for this requirement
after commit 201007ef707a8 ("PCI: Enable PASID only when ACS RR & UF
enabled on upstream path"), which made this requirement implicit.

Restore the check to make it explicit that the PASID interfaces only
support devices belonging to single-device groups.

Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
---
 drivers/iommu/iommu.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 71b9c41f2a9e..f1eba60e573f 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -3408,6 +3408,11 @@ int iommu_attach_device_pasid(struct iommu_domain *domain,
 		return -ENODEV;
 
 	mutex_lock(&group->mutex);
+	if (list_count_nodes(&group->devices) != 1) {
+		ret = -EINVAL;
+		goto out_unlock;
+	}
+
 	curr = xa_cmpxchg(&group->pasid_array, pasid, NULL, domain, GFP_KERNEL);
 	if (curr) {
 		ret = xa_err(curr) ? : -EBUSY;
-- 
2.34.1