iommu/intel: Fix ACS path checking

SR-IOV can create buses without a bridge.  There may be other cases
where this happens as well.  In these cases skip to the parent bus
and continue testing devices there.
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Tested-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

drivers/iommu/intel-iommu.c

@@ -4125,8 +4125,13 @@ static int intel_iommu_add_device(struct device *dev)
 	} else
 		dma_pdev = pci_dev_get(pdev);
 
+	/* Account for quirked devices */
 	swap_pci_ref(&dma_pdev, pci_get_dma_source(dma_pdev));
 
+	/*
+	 * If it's a multifunction device that does not support our
+	 * required ACS flags, add to the same group as function 0.
+	 */
 	if (dma_pdev->multifunction &&
 	    !pci_acs_enabled(dma_pdev, REQ_ACS_FLAGS))
 		swap_pci_ref(&dma_pdev,
@@ -4134,14 +4139,28 @@ static int intel_iommu_add_device(struct device *dev)
 					  PCI_DEVFN(PCI_SLOT(dma_pdev->devfn),
 					  0)));
 
+	/*
+	 * Devices on the root bus go through the iommu.  If that's not us,
+	 * find the next upstream device and test ACS up to the root bus.
+	 * Finding the next device may require skipping virtual buses.
+	 */
 	while (!pci_is_root_bus(dma_pdev->bus)) {
-		if (pci_acs_path_enabled(dma_pdev->bus->self,
-					 NULL, REQ_ACS_FLAGS))
+		struct pci_bus *bus = dma_pdev->bus;
+
+		while (!bus->self) {
+			if (!pci_is_root_bus(bus))
+				bus = bus->parent;
+			else
+				goto root_bus;
+		}
+
+		if (pci_acs_path_enabled(bus->self, NULL, REQ_ACS_FLAGS))
 			break;
 
-		swap_pci_ref(&dma_pdev, pci_dev_get(dma_pdev->bus->self));
+		swap_pci_ref(&dma_pdev, pci_dev_get(bus->self));
 	}
 
+root_bus:
 	group = iommu_group_get(&dma_pdev->dev);
 	pci_dev_put(dma_pdev);
 	if (!group) {