diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c b/drivers/iommu/arm/arm-smmu/arm-smmu.c
index 3f0f3044067e..3739699cb101 100644
--- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
+++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
@@ -2932,8 +2932,10 @@ static void arm_smmu_device_reset(struct arm_smmu_device *smmu)
 	 * Reset stream mapping groups: Initial values mark all SMRn as
 	 * invalid and all S2CRn as bypass unless overridden.
 	 */
+	mutex_lock(&smmu->stream_map_mutex);
 	for (i = 0; i < smmu->num_mapping_groups; ++i)
 		arm_smmu_write_sme(smmu, i);
+	mutex_unlock(&smmu->stream_map_mutex);
 
 	/* Make sure all context banks are disabled and clear CB_FSR  */
 	for (i = 0; i < smmu->num_context_banks; ++i) {