[PATCH v2 3/3] iommu/arm-smmu-v3-iommufd: Require exactly one Stream ID for a vDEVICE

[Nicolin Chen]

arm_vsmmu_vsid_to_sid() maps a guest's vSID to a single physical Stream ID
taken from master->streams[0], assuming a device has exactly one stream. A
device with several streams gets only its first one mapped, so a guest vSID
invalidation cannot reach the others' ATC and IOTLB entries; a device with
none makes master->streams a ZERO_SIZE_PTR, read out of bounds.

Add an arm_vsmmu_vdevice_init() op to reject the vDEVICE with -EOPNOTSUPP
when master->num_streams is not one, rather than mapping it silently.

Fixes: d68beb276ba26 ("iommu/arm-smmu-v3: Support IOMMU_HWPT_INVALIDATE using a VIOMMU object")
Reviewed-by: Kevin Tian <kevin.tian at intel.com>
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Nicolin Chen <nicolinc at nvidia.com>
---
 .../iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c   | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
index 1e9f7d2de3441..85ebfdb3d2a7a 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
@@ -297,6 +297,20 @@ static int arm_vsmmu_vsid_to_sid(struct arm_vsmmu *vsmmu, u32 vsid, u32 *sid)
 	return ret;
 }
 
+static int arm_vsmmu_vdevice_init(struct iommufd_vdevice *vdev)
+{
+	struct device *dev = iommufd_vdevice_to_device(vdev);
+	struct arm_smmu_master *master = dev_iommu_priv_get(dev);
+
+	/*
+	 * arm_vsmmu_vsid_to_sid() maps a vSID to master->streams[0] alone, so
+	 * more streams would leave the rest stale and none reads out of bounds.
+	 */
+	if (master->num_streams != 1)
+		return -EOPNOTSUPP;
+	return 0;
+}
+
 /* This is basically iommu_viommu_arm_smmuv3_invalidate in u64 for conversion */
 struct arm_vsmmu_invalidation_cmd {
 	union {
@@ -403,6 +417,7 @@ int arm_vsmmu_cache_invalidate(struct iommufd_viommu *viommu,
 static const struct iommufd_viommu_ops arm_vsmmu_ops = {
 	.alloc_domain_nested = arm_vsmmu_alloc_domain_nested,
 	.cache_invalidate = arm_vsmmu_cache_invalidate,
+	.vdevice_init = arm_vsmmu_vdevice_init,
 };
 
 size_t arm_smmu_get_viommu_size(struct device *dev,
-- 
2.43.0