diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
index 21d02b0d907c..5a02d0776a66 100644
--- a/drivers/iommu/amd_iommu.c
+++ b/drivers/iommu/amd_iommu.c
@@ -287,14 +287,27 @@ static struct pci_dev *get_isolation_root(struct pci_dev *pdev)
 
 	/*
 	 * If it's a multifunction device that does not support our
-	 * required ACS flags, add to the same group as function 0.
+	 * required ACS flags, add to the same group as lowest numbered
+	 * function that also does not suport the required ACS flags.
 	 */
 	if (dma_pdev->multifunction &&
-	    !pci_acs_enabled(dma_pdev, REQ_ACS_FLAGS))
-		swap_pci_ref(&dma_pdev,
-			     pci_get_slot(dma_pdev->bus,
-					  PCI_DEVFN(PCI_SLOT(dma_pdev->devfn),
-					  0)));
+	    !pci_acs_enabled(dma_pdev, REQ_ACS_FLAGS)) {
+		u8 i, slot = PCI_SLOT(dma_pdev->devfn);
+
+		for (i = 0; i < 8; i++) {
+			struct pci_dev *tmp;
+
+			tmp = pci_get_slot(dma_pdev->bus, PCI_DEVFN(slot, i));
+			if (!tmp)
+				continue;
+
+			if (!pci_acs_enabled(tmp, REQ_ACS_FLAGS)) {
+				swap_pci_ref(&dma_pdev, tmp);
+				break;
+			}
+			pci_dev_put(tmp);
+		}
+	}
 
 	/*
 	 * Devices on the root bus go through the iommu.  If that's not us,
diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index b4f0e28dfa41..eec0d3e04bf5 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -4182,14 +4182,27 @@ static int intel_iommu_add_device(struct device *dev)
 
 	/*
 	 * If it's a multifunction device that does not support our
-	 * required ACS flags, add to the same group as function 0.
+	 * required ACS flags, add to the same group as lowest numbered
+	 * function that also does not suport the required ACS flags.
 	 */
 	if (dma_pdev->multifunction &&
-	    !pci_acs_enabled(dma_pdev, REQ_ACS_FLAGS))
-		swap_pci_ref(&dma_pdev,
-			     pci_get_slot(dma_pdev->bus,
-					  PCI_DEVFN(PCI_SLOT(dma_pdev->devfn),
-					  0)));
+	    !pci_acs_enabled(dma_pdev, REQ_ACS_FLAGS)) {
+		u8 i, slot = PCI_SLOT(dma_pdev->devfn);
+
+		for (i = 0; i < 8; i++) {
+			struct pci_dev *tmp;
+
+			tmp = pci_get_slot(dma_pdev->bus, PCI_DEVFN(slot, i));
+			if (!tmp)
+				continue;
+
+			if (!pci_acs_enabled(tmp, REQ_ACS_FLAGS)) {
+				swap_pci_ref(&dma_pdev, tmp);
+				break;
+			}
+			pci_dev_put(tmp);
+		}
+	}
 
 	/*
 	 * Devices on the root bus go through the iommu.  If that's not us,