[PATCH v2 2/2] pci: allow slot_reserved_mask to be ignored with manual slot assignment

[Chuck Zmudzinski <brchuckz@xxxxxxx>]

Commit 4f67543bb8c5 ("xen/pt: reserve PCI slot 2 for Intel igd-passthru")
uses slot_reserved_mask to reserve slot 2 for the Intel IGD for the
xenfv machine when the guest is configured for igd-passthru.

A desired extension to that commit is to allow use of the reserved slot
if the administrator manually configures a device to use the reserved
slot. Currently, slot_reserved_mask is enforced unconditionally. With
this patch, the pci bus can be configured so the slot is only reserved
if the pci device to be added to the bus is configured for automatic
slot assignment.

To enable the desired behavior of slot_reserved_mask machine, add a
boolean member enforce_slot_reserved_mask_manual to struct PCIBus and
add a function pci_bus_ignore_slot_reserved_mask_manual which can be
called to change the default behavior of always enforcing
slot_reserved_mask so, in that case, slot_reserved_mask is only enforced
when the pci device being added is configured for automatic slot
assignment.

Call the new pci_bus_ignore_slot_reserved_mask_manual function after
creating the pci bus for the pc/i440fx/xenfv machine type to implement
the desired behavior of causing slot_reserved_mask to only apply when
the pci device to be added to a pc/i440fx/xenfv machine is configured
for automatic slot assignment.

Link: 
https://lore.kernel.org/qemu-devel/20230106064838-mutt-send-email-mst@xxxxxxxxxx/
Signed-off-by: Chuck Zmudzinski <brchuckz@xxxxxxx>
---
Changelog

v2: Change Subject of patch from
    "pci: add enforce_slot_reserved_mask_manual property" To
    "pci: allow slot_reserved_mask to be ignored with manual slot assignment"

    Add pci_bus_ignore_slot_reserved_mask_manual function

    Call pci_bus_ignore_slot_reserved_mask_manual at appropriate place
    in hw/pci-host/i440fx.c

 hw/pci-host/i440fx.c     |  1 +
 hw/pci/pci.c             | 14 +++++++++++++-
 include/hw/pci/pci.h     |  1 +
 include/hw/pci/pci_bus.h |  1 +
 4 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/hw/pci-host/i440fx.c b/hw/pci-host/i440fx.c
index 262f82c303..8e00b88926 100644
--- a/hw/pci-host/i440fx.c
+++ b/hw/pci-host/i440fx.c
@@ -257,6 +257,7 @@ PCIBus *i440fx_init(const char *pci_type,
     s = PCI_HOST_BRIDGE(dev);
     b = pci_root_bus_new(dev, NULL, pci_address_space,
                          address_space_io, 0, TYPE_PCI_BUS);
+    pci_bus_ignore_slot_reserved_mask_manual(b);
     s->bus = b;
     object_property_add_child(qdev_get_machine(), "i440fx", OBJECT(dev));
     sysbus_realize_and_unref(SYS_BUS_DEVICE(dev), &error_fatal);
diff --git a/hw/pci/pci.c b/hw/pci/pci.c
index 8a87ccc8b0..670ecc6986 100644
--- a/hw/pci/pci.c
+++ b/hw/pci/pci.c
@@ -501,6 +501,7 @@ static void pci_root_bus_internal_init(PCIBus *bus, 
DeviceState *parent,
     assert(PCI_FUNC(devfn_min) == 0);
     bus->devfn_min = devfn_min;
     bus->slot_reserved_mask = 0x0;
+    bus->enforce_slot_reserved_mask_manual = true;
     bus->address_space_mem = address_space_mem;
     bus->address_space_io = address_space_io;
     bus->flags |= PCI_BUS_IS_ROOT;
@@ -1116,6 +1117,17 @@ static bool pci_bus_devfn_reserved(PCIBus *bus, int 
devfn)
     return bus->slot_reserved_mask & (1UL << PCI_SLOT(devfn));
 }
 
+static bool pci_bus_devfn_reserved_manual(PCIBus *bus, int devfn)
+{
+    return bus->enforce_slot_reserved_mask_manual &&
+            (bus->slot_reserved_mask & (1UL << PCI_SLOT(devfn)));
+}
+
+void pci_bus_ignore_slot_reserved_mask_manual(PCIBus *bus)
+{
+    bus->enforce_slot_reserved_mask_manual = false;
+}
+
 uint32_t pci_bus_get_slot_reserved_mask(PCIBus *bus)
 {
     return bus->slot_reserved_mask;
@@ -1164,7 +1176,7 @@ static PCIDevice *do_pci_register_device(PCIDevice 
*pci_dev,
                    "or reserved", name);
         return NULL;
     found: ;
-    } else if (pci_bus_devfn_reserved(bus, devfn)) {
+    } else if (pci_bus_devfn_reserved_manual(bus, devfn)) {
         error_setg(errp, "PCI: slot %d function %d not available for %s,"
                    " reserved",
                    PCI_SLOT(devfn), PCI_FUNC(devfn), name);
diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
index 935b4b91b4..48d29ec234 100644
--- a/include/hw/pci/pci.h
+++ b/include/hw/pci/pci.h
@@ -287,6 +287,7 @@ void pci_bus_irqs(PCIBus *bus, pci_set_irq_fn set_irq,
 void pci_bus_map_irqs(PCIBus *bus, pci_map_irq_fn map_irq);
 void pci_bus_irqs_cleanup(PCIBus *bus);
 int pci_bus_get_irq_level(PCIBus *bus, int irq_num);
+void pci_bus_ignore_slot_reserved_mask_manual(PCIBus *bus);
 uint32_t pci_bus_get_slot_reserved_mask(PCIBus *bus);
 void pci_bus_set_slot_reserved_mask(PCIBus *bus, uint32_t mask);
 void pci_bus_clear_slot_reserved_mask(PCIBus *bus, uint32_t mask);
diff --git a/include/hw/pci/pci_bus.h b/include/hw/pci/pci_bus.h
index 5653175957..e0f15ee9be 100644
--- a/include/hw/pci/pci_bus.h
+++ b/include/hw/pci/pci_bus.h
@@ -37,6 +37,7 @@ struct PCIBus {
     void *iommu_opaque;
     uint8_t devfn_min;
     uint32_t slot_reserved_mask;
+    bool enforce_slot_reserved_mask_manual;
     pci_set_irq_fn set_irq;
     pci_map_irq_fn map_irq;
     pci_route_irq_fn route_intx_to_irq;
-- 
2.39.2