From 72cc005ad139d9d5d4bf2cb7402cf730c6726fd3 Mon Sep 17 00:00:00 2001
From: Cornelia Huck <cohuck@redhat.com>
Date: Wed, 17 Apr 2019 13:57:37 +0100
Subject: [PATCH 20/24] s390x/pci: Fix hotplugging of PCI bridges

RH-Author: Cornelia Huck <cohuck@redhat.com>
Message-id: <20190417135741.25297-21-cohuck@redhat.com>
Patchwork-id: 85801
O-Subject: [RHEL-8.1.0 qemu-kvm PATCH v2 20/24] s390x/pci: Fix hotplugging of PCI bridges
Bugzilla: 1699070
RH-Acked-by: David Hildenbrand <david@redhat.com>
RH-Acked-by: Thomas Huth <thuth@redhat.com>
RH-Acked-by: Jens Freimann <jfreimann@redhat.com>

From: David Hildenbrand <david@redhat.com>

When hotplugging a PCI bridge right now to the root port, we resolve
pci_get_bus(pdev)->parent_dev, which results in a SEGFAULT. Hotplugging
really only works right now when hotplugging to another bridge.

Instead, we have to properly check if we are already at the root.

Let's cleanup the code while at it a bit and factor out updating the
subordinate bus number into a separate function. The check for
"old_nr < nr" is right now not strictly necessary, but makes it more
obvious what is actually going on.

Most probably fixing up the topology is not our responsibility when
hotplugging. The guest has to sort this out. But let's keep it for now
and only fix current code to not crash.

Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20190130155733.32742-3-david@redhat.com>
Reviewed-by: Collin Walling <walling@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
(cherry picked from commit 150f462538a6f3b78efe785c911669375032b0d2)
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>
---
 hw/s390x/s390-pci-bus.c | 28 +++++++++++++++++++---------
 1 file changed, 19 insertions(+), 9 deletions(-)

diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
index 309ad79..a0f7245 100644
--- a/hw/s390x/s390-pci-bus.c
+++ b/hw/s390x/s390-pci-bus.c
@@ -881,6 +881,21 @@ static void s390_pcihost_pre_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
     }
 }
 
+static void s390_pci_update_subordinate(PCIDevice *dev, uint32_t nr)
+{
+    uint32_t old_nr;
+
+    pci_default_write_config(dev, PCI_SUBORDINATE_BUS, nr, 1);
+    while (!pci_bus_is_root(pci_get_bus(dev))) {
+        dev = pci_get_bus(dev)->parent_dev;
+
+        old_nr = pci_default_read_config(dev, PCI_SUBORDINATE_BUS, 1);
+        if (old_nr < nr) {
+            pci_default_write_config(dev, PCI_SUBORDINATE_BUS, nr, 1);
+        }
+    }
+}
+
 static void s390_pcihost_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
                               Error **errp)
 {
@@ -889,26 +904,21 @@ static void s390_pcihost_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
     S390PCIBusDevice *pbdev = NULL;
 
     if (object_dynamic_cast(OBJECT(dev), TYPE_PCI_BRIDGE)) {
-        BusState *bus;
         PCIBridge *pb = PCI_BRIDGE(dev);
-        PCIDevice *pdev = PCI_DEVICE(dev);
 
+        pdev = PCI_DEVICE(dev);
         pci_bridge_map_irq(pb, dev->id, s390_pci_map_irq);
         pci_setup_iommu(&pb->sec_bus, s390_pci_dma_iommu, s);
 
-        bus = BUS(&pb->sec_bus);
-        qbus_set_hotplug_handler(bus, DEVICE(s), errp);
+        qbus_set_hotplug_handler(BUS(&pb->sec_bus), DEVICE(s), errp);
 
         if (dev->hotplugged) {
             pci_default_write_config(pdev, PCI_PRIMARY_BUS,
                                      pci_dev_bus_num(pdev), 1);
             s->bus_no += 1;
             pci_default_write_config(pdev, PCI_SECONDARY_BUS, s->bus_no, 1);
-            do {
-                pdev = pci_get_bus(pdev)->parent_dev;
-                pci_default_write_config(pdev, PCI_SUBORDINATE_BUS,
-                                         s->bus_no, 1);
-            } while (pci_get_bus(pdev) && pci_dev_bus_num(pdev));
+
+            s390_pci_update_subordinate(pdev, s->bus_no);
         }
     } else if (object_dynamic_cast(OBJECT(dev), TYPE_PCI_DEVICE)) {
         pdev = PCI_DEVICE(dev);
-- 
1.8.3.1