From: Ani Sinha <anisinha@redhat.com>

PCIe downstream ports only have a single device 0, so PCI Express devices can
only be plugged into slot 0 on a PCIe port. Add a warning to let users know
when the invalid configuration is used. We may enforce this more strongly later
once we get more clarity on whether we are introducing a bad regression for
users currently using the wrong configuration.

The change has been tested to not break or alter behaviors of ARI capable
devices by instantiating seven vfs on an emulated igb device (the maximum
number of vfs the igb device supports). The vfs are instantiated correctly
and are seen to have non-zero device/slot numbers in the conventional PCI BDF
representation.

CC: jusual@redhat.com
CC: imammedo@redhat.com
CC: mst@redhat.com
CC: akihiko.odaki@daynix.com

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2128929
Signed-off-by: Ani Sinha <anisinha@redhat.com>
Reviewed-by: Julia Suvorova <jusual@redhat.com>
Message-Id: <20230705115925.5339-6-anisinha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Akihiko Odaki <akihiko.odaki@daynix.com>
---
 hw/pci/pci.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/hw/pci/pci.c b/hw/pci/pci.c
index fb17138f7d..4b14f31859 100644
--- a/hw/pci/pci.c
+++ b/hw/pci/pci.c
@@ -65,6 +65,7 @@ bool pci_available = true;
 static char *pcibus_get_dev_path(DeviceState *dev);
 static char *pcibus_get_fw_dev_path(DeviceState *dev);
 static void pcibus_reset(BusState *qbus);
+static bool pcie_has_upstream_port(PCIDevice *dev);
 
 static Property pci_props[] = {
     DEFINE_PROP_PCI_DEVFN("addr", PCIDevice, devfn, -1),
@@ -2121,6 +2122,25 @@ static void pci_qdev_realize(DeviceState *qdev, Error **errp)
         }
     }
 
+    /*
+     * A PCIe Downstream Port that do not have ARI Forwarding enabled must
+     * associate only Device 0 with the device attached to the bus
+     * representing the Link from the Port (PCIe base spec rev 4.0 ver 0.3,
+     * sec 7.3.1).
+     * With ARI, PCI_SLOT() can return non-zero value as the traditional
+     * 5-bit Device Number and 3-bit Function Number fields in its associated
+     * Routing IDs, Requester IDs and Completer IDs are interpreted as a
+     * single 8-bit Function Number. Hence, ignore ARI capable devices.
+     */
+    if (pci_is_express(pci_dev) &&
+        !pcie_find_capability(pci_dev, PCI_EXT_CAP_ID_ARI) &&
+        pcie_has_upstream_port(pci_dev) &&
+        PCI_SLOT(pci_dev->devfn)) {
+        warn_report("PCI: slot %d is not valid for %s,"
+                    " parent device only allows plugging into slot 0.",
+                    PCI_SLOT(pci_dev->devfn), pci_dev->name);
+    }
+
     if (pci_dev->failover_pair_id) {
         if (!pci_bus_is_express(pci_get_bus(pci_dev))) {
             error_setg(errp, "failover primary device must be on "
-- 
MST