[PATCH v2] vfio/pci: Introduce x-pci-class-code option

[Tomita Moeko <tomitamoeko@gmail.com>]

Introduce x-pci-class-code option to allow users to override PCI class
code of a device, similar to the existing x-pci-vendor-id option. Only
the lower 24 bits of this option are used, though a uint32 is used here
for determining whether the value is valid and set by user.

Additionally, to prevent exposing VGA ranges on non-VGA devices, the
x-vga=on option requires x-pci-class-code is either unset or set to
VGA controller class.

This is mainly intended for IGD devices that expose themselves either
as VGA controller (primary display) or Display controller (non-primary
display). The UEFI GOP driver depends on the device reporting a VGA
controller class code (0x030000).

Signed-off-by: Tomita Moeko <tomitamoeko@gmail.com>
---
v2:
* Add vdev class code check in vfio_populate_vga().
* Fix type in trace-events.
Link: https://lore.kernel.org/all/20250524153102.19747-1-tomitamoeko@gmail.com/

 hw/vfio/pci.c        | 25 +++++++++++++++++++++++++
 hw/vfio/pci.h        |  1 +
 hw/vfio/trace-events |  1 +
 3 files changed, 27 insertions(+)

diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index b1250d85bf..d57cb7356e 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -2726,6 +2726,14 @@ bool vfio_populate_vga(VFIOPCIDevice *vdev, Error **errp)
         return false;
     }
 
+    /* vdev class should be either unmodified (PCI_ANY_ID), or VGA controller */
+    if ((vdev->class_code != PCI_ANY_ID) &&
+        (vdev->class_code != (PCI_CLASS_DISPLAY_VGA << 8)) &&
+        (vdev->class_code != (PCI_CLASS_NOT_DEFINED_VGA << 8))) {
+        error_setg(errp, "vdev is not a VGA device");
+        return false;
+    }
+
     if (!(reg_info->flags & VFIO_REGION_INFO_FLAG_READ) ||
         !(reg_info->flags & VFIO_REGION_INFO_FLAG_WRITE) ||
         reg_info->size < 0xbffff + 1) {
@@ -3092,6 +3100,21 @@ static bool vfio_pci_config_setup(VFIOPCIDevice *vdev, Error **errp)
                                               vdev->sub_device_id);
     }
 
+    /*
+     * Class code is a 24-bit value at config space 0x09. Allow overriding it
+     * with any 24-bit value.
+     */
+    if (vdev->class_code != PCI_ANY_ID) {
+        if (vdev->class_code > 0xffffff) {
+            error_setg(errp, "invalid PCI class code provided");
+            return false;
+        }
+        /* Higher 24 bits of PCI_CLASS_REVISION are class code */
+        vfio_add_emulated_long(vdev, PCI_CLASS_REVISION,
+                               vdev->class_code << 8, ~0xff);
+        trace_vfio_pci_emulated_class_code(vbasedev->name, vdev->class_code);
+    }
+
     /* QEMU can change multi-function devices to single function, or reverse */
     vdev->emulated_config_bits[PCI_HEADER_TYPE] =
                                               PCI_HEADER_TYPE_MULTI_FUNCTION;
@@ -3489,6 +3512,8 @@ static const Property vfio_pci_dev_properties[] = {
                        sub_vendor_id, PCI_ANY_ID),
     DEFINE_PROP_UINT32("x-pci-sub-device-id", VFIOPCIDevice,
                        sub_device_id, PCI_ANY_ID),
+    DEFINE_PROP_UINT32("x-pci-class-code", VFIOPCIDevice,
+                       class_code, PCI_ANY_ID),
     DEFINE_PROP_UINT32("x-igd-gms", VFIOPCIDevice, igd_gms, 0),
     DEFINE_PROP_UNSIGNED_NODEFAULT("x-nv-gpudirect-clique", VFIOPCIDevice,
                                    nv_gpudirect_clique,
diff --git a/hw/vfio/pci.h b/hw/vfio/pci.h
index 5ce0fb916f..587eb8cc9a 100644
--- a/hw/vfio/pci.h
+++ b/hw/vfio/pci.h
@@ -156,6 +156,7 @@ struct VFIOPCIDevice {
     uint32_t device_id;
     uint32_t sub_vendor_id;
     uint32_t sub_device_id;
+    uint32_t class_code;
     uint32_t features;
 #define VFIO_FEATURE_ENABLE_VGA_BIT 0
 #define VFIO_FEATURE_ENABLE_VGA (1 << VFIO_FEATURE_ENABLE_VGA_BIT)
diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events
index e90ec9bff8..e8d585b49a 100644
--- a/hw/vfio/trace-events
+++ b/hw/vfio/trace-events
@@ -46,6 +46,7 @@ vfio_pci_emulated_vendor_id(const char *name, uint16_t val) "%s 0x%04x"
 vfio_pci_emulated_device_id(const char *name, uint16_t val) "%s 0x%04x"
 vfio_pci_emulated_sub_vendor_id(const char *name, uint16_t val) "%s 0x%04x"
 vfio_pci_emulated_sub_device_id(const char *name, uint16_t val) "%s 0x%04x"
+vfio_pci_emulated_class_code(const char *name, uint32_t val) "%s 0x%06x"
 
 # pci-quirks.c
 vfio_quirk_rom_in_denylist(const char *name, uint16_t vid, uint16_t did) "%s %04x:%04x"
-- 
2.47.2