xen PV passthru: assign SR-IOV virtual functions to separate virtual slots

VFs are reported as single-function devices in PCI_HEADER_TYPE, which
causes pci_scan_slot() in the PV domU to skip all VFs beyond #0 in the
pciback-provided slot. Avoid this by assigning each VF to a separate
virtual slot.
Acked-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/xen/xen-pciback/vpci.c

@@ -89,9 +89,15 @@ static int __xen_pcibk_add_pci_dev(struct xen_pcibk_device *pdev,
 
 	mutex_lock(&vpci_dev->lock);
 
-	/* Keep multi-function devices together on the virtual PCI bus */
+	/*
+	 * Keep multi-function devices together on the virtual PCI bus, except
+	 * virtual functions.
+	 */
+	if (!dev->is_virtfn) {
 		for (slot = 0; slot < PCI_SLOT_MAX; slot++) {
-		if (!list_empty(&vpci_dev->dev_list[slot])) {
+			if (list_empty(&vpci_dev->dev_list[slot]))
+				continue;
+
 			t = list_entry(list_first(&vpci_dev->dev_list[slot]),
 				       struct pci_dev_entry, list);
 
@@ -116,7 +122,7 @@ static int __xen_pcibk_add_pci_dev(struct xen_pcibk_device *pdev,
 			       pci_name(dev), slot);
 			list_add_tail(&dev_entry->list,
 				      &vpci_dev->dev_list[slot]);
-			func = PCI_FUNC(dev->devfn);
+			func = dev->is_virtfn ? 0 : PCI_FUNC(dev->devfn);
 			goto unlock;
 		}
 	}