hw/pci: Use -1 as the default value for rombar

vfio_pci_size_rom() distinguishes whether rombar is explicitly set to 1
by checking dev->opts, bypassing the QOM property infrastructure.

Use -1 as the default value for rombar to tell if the user explicitly
set it to 1. The property is also converted from unsigned to signed.
-1 is signed so it is safe to give it a new meaning. The values in
[2 ^ 31, 2 ^ 32) become invalid, but nobody should have typed these
values by chance.

Suggested-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20250104-reuse-v18-13-c349eafd8673@daynix.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

hw/pci/pci.c

@@ -85,7 +85,7 @@ static const Property pci_props[] = {
     DEFINE_PROP_PCI_DEVFN("addr", PCIDevice, devfn, -1),
     DEFINE_PROP_STRING("romfile", PCIDevice, romfile),
     DEFINE_PROP_UINT32("romsize", PCIDevice, romsize, UINT32_MAX),
-    DEFINE_PROP_UINT32("rombar",  PCIDevice, rom_bar, 1),
+    DEFINE_PROP_INT32("rombar",  PCIDevice, rom_bar, -1),
     DEFINE_PROP_BIT("multifunction", PCIDevice, cap_present,
                     QEMU_PCI_CAP_MULTIFUNCTION_BITNR, false),
     DEFINE_PROP_BIT("x-pcie-lnksta-dllla", PCIDevice, cap_present,

hw/vfio/pci.c

@@ -1012,7 +1012,6 @@ static void vfio_pci_size_rom(VFIOPCIDevice *vdev)
 {
     uint32_t orig, size = cpu_to_le32((uint32_t)PCI_ROM_ADDRESS_MASK);
     off_t offset = vdev->config_offset + PCI_ROM_ADDRESS;
-    DeviceState *dev = DEVICE(vdev);
     char *name;
     int fd = vdev->vbasedev.fd;
 
@@ -1046,12 +1045,12 @@ static void vfio_pci_size_rom(VFIOPCIDevice *vdev)
     }
 
     if (vfio_opt_rom_in_denylist(vdev)) {
-        if (dev->opts && qdict_haskey(dev->opts, "rombar")) {
+        if (vdev->pdev.rom_bar > 0) {
             warn_report("Device at %s is known to cause system instability"
                         " issues during option rom execution",
                         vdev->vbasedev.name);
             error_printf("Proceeding anyway since user specified"
-                         " non zero value for rombar\n");
+                         " positive value for rombar\n");
         } else {
             warn_report("Rom loading for device at %s has been disabled"
                         " due to system instability issues",

include/hw/pci/pci_device.h

@@ -148,7 +148,7 @@ struct PCIDevice {
     uint32_t romsize;
     bool has_rom;
     MemoryRegion rom;
-    uint32_t rom_bar;
+    int32_t rom_bar;
 
     /* INTx routing notifier */
     PCIINTxRoutingNotifier intx_routing_notifier;