pcie: Simplify pci_adjust_config_limit()

Since c2077e2c "pci: Adjust PCI config limit based on bus topology",
pci_adjust_config_limit() has been used in the config space read and write
paths to only permit access to extended config space on buses which permit
it.  Specifically it prevents access on devices below a vanilla-PCI bus via
some combination of bridges, even if both the host bridge and the device
itself are PCI-E.

It accomplishes this with a somewhat complex call up the chain of bridges
to see if any of them prohibit extended config space access.  This is
overly complex, since we can always know if the bus will support such
access at the point it is constructed.

This patch simplifies the test by using a flag in the PCIBus instance
indicating whether extended configuration space is accessible.  It is
false for vanilla PCI buses.  For PCI-E buses, it is true for root
buses and equal to the parent bus's's capability otherwise.

For the special case of sPAPR's paravirtualized PCI root bus, which
acts mostly like vanilla PCI, but does allow extended config space
access, we override the default value of the flag from the host bridge
code.

This should cause no behavioural change.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Greg Kurz <groug@kaod.org>
Message-Id: <20190513061939.3464-4-david@gibson.dropbear.id.au>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

2 files changed, 26 insertions, 28 deletions

diff --git a/hw/pci/pci.c b/hw/pci/pci.c
index b386777..7e5f8d0 100644
--- a/hw/pci/pci.c
+++ b/hw/pci/pci.c
@@ -120,6 +120,27 @@ static void pci_bus_realize(BusState *qbus, Error **errp)
     vmstate_register(NULL, -1, &vmstate_pcibus, bus);
 }
 
+static void pcie_bus_realize(BusState *qbus, Error **errp)
+{
+    PCIBus *bus = PCI_BUS(qbus);
+
+    pci_bus_realize(qbus, errp);
+
+    /*
+     * A PCI-E bus can support extended config space if it's the root
+     * bus, or if the bus/bridge above it does as well
+     */
+    if (pci_bus_is_root(bus)) {
+        bus->flags |= PCI_BUS_EXTENDED_CONFIG_SPACE;
+    } else {
+        PCIBus *parent_bus = pci_get_bus(bus->parent_dev);
+
+        if (pci_bus_allows_extended_config_space(parent_bus)) {
+            bus->flags |= PCI_BUS_EXTENDED_CONFIG_SPACE;
+        }
+    }
+}
+
 static void pci_bus_unrealize(BusState *qbus, Error **errp)
 {
     PCIBus *bus = PCI_BUS(qbus);
@@ -142,11 +163,6 @@ static uint16_t pcibus_numa_node(PCIBus *bus)
     return NUMA_NODE_UNASSIGNED;
 }
 
-static bool pcibus_allows_extended_config_space(PCIBus *bus)
-{
-    return false;
-}
-
 static void pci_bus_class_init(ObjectClass *klass, void *data)
 {
     BusClass *k = BUS_CLASS(klass);
@@ -161,7 +177,6 @@ static void pci_bus_class_init(ObjectClass *klass, void *data)
 
     pbc->bus_num = pcibus_num;
     pbc->numa_node = pcibus_numa_node;
-    pbc->allows_extended_config_space = pcibus_allows_extended_config_space;
 }
 
 static const TypeInfo pci_bus_info = {
@@ -182,16 +197,11 @@ static const TypeInfo conventional_pci_interface_info = {
     .parent        = TYPE_INTERFACE,
 };
 
-static bool pciebus_allows_extended_config_space(PCIBus *bus)
-{
-    return true;
-}
-
 static void pcie_bus_class_init(ObjectClass *klass, void *data)
 {
-    PCIBusClass *pbc = PCI_BUS_CLASS(klass);
+    BusClass *k = BUS_CLASS(klass);
 
-    pbc->allows_extended_config_space = pciebus_allows_extended_config_space;
+    k->realize = pcie_bus_realize;
 }
 
 static const TypeInfo pcie_bus_info = {
@@ -410,11 +420,6 @@ bool pci_bus_is_express(PCIBus *bus)
     return object_dynamic_cast(OBJECT(bus), TYPE_PCIE_BUS);
 }
 
-bool pci_bus_allows_extended_config_space(PCIBus *bus)
-{
-    return PCI_BUS_GET_CLASS(bus)->allows_extended_config_space(bus);
-}
-
 void pci_root_bus_new_inplace(PCIBus *bus, size_t bus_size, DeviceState *parent,
                               const char *name,
                               MemoryRegion *address_space_mem,
diff --git a/hw/pci/pci_host.c b/hw/pci/pci_host.c
index 9d64b2e..5f34972 100644
--- a/hw/pci/pci_host.c
+++ b/hw/pci/pci_host.c
@@ -53,16 +53,9 @@ static inline PCIDevice *pci_dev_find_by_addr(PCIBus *bus, uint32_t addr)
 
 static void pci_adjust_config_limit(PCIBus *bus, uint32_t *limit)
 {
-    if (*limit > PCI_CONFIG_SPACE_SIZE) {
-        if (!pci_bus_allows_extended_config_space(bus)) {
-            *limit = PCI_CONFIG_SPACE_SIZE;
-            return;
-        }
-
-        if (!pci_bus_is_root(bus)) {
-            PCIDevice *bridge = pci_bridge_get_device(bus);
-            pci_adjust_config_limit(pci_get_bus(bridge), limit);
-        }
+    if ((*limit > PCI_CONFIG_SPACE_SIZE) &&
+        !pci_bus_allows_extended_config_space(bus)) {
+        *limit = PCI_CONFIG_SPACE_SIZE;
     }
 }