[PATCH v7 5/6] hw/pci: ensure PCIE devices are plugged into only slot 0 of PCIE port

[Ani Sinha <anisinha@redhat.com>]

PCI Express ports only have one slot, 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 on once
we get more clarity on whether we are introducing a bad regression for users
currenly 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 linux igb driver supports). The vfs 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>
---
 hw/pci/pci.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/hw/pci/pci.c b/hw/pci/pci.c
index e2eb4c3b4a..47517ba3db 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 +2122,20 @@ static void pci_qdev_realize(DeviceState *qdev, Error **errp)
         }
     }
 
+    /*
+     * With SRIOV and ARI, vfs can have non-zero slot in the conventional
+     * PCI interpretation as all five bits reserved for slot addresses are
+     * also used for function bits for the various vfs. Ignore that case.
+     */
+    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 "
-- 
2.39.1