vfio/pci: Introduce x-pci-class-code option

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 ensure VGA ranges are only exposed on VGA devices,
pci_register_vga() is now called in vfio_pci_config_setup(), after
the class code override is completed.

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>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20250708145211.6179-1-tomitamoeko@gmail.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>

3 files changed, 28 insertions, 8 deletions

diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index 1093b28..910042c 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -2893,10 +2893,6 @@ bool vfio_populate_vga(VFIOPCIDevice *vdev, Error **errp)
                           "vfio-vga-io@0x3c0",
                           QEMU_PCI_VGA_IO_HI_SIZE);
 
-    pci_register_vga(&vdev->pdev, &vdev->vga->region[QEMU_PCI_VGA_MEM].mem,
-                     &vdev->vga->region[QEMU_PCI_VGA_IO_LO].mem,
-                     &vdev->vga->region[QEMU_PCI_VGA_IO_HI].mem);
-
     return true;
 }
 
@@ -3228,6 +3224,23 @@ 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);
+    } else {
+        vdev->class_code = pci_get_long(pdev->config + PCI_CLASS_REVISION) >> 8;
+    }
+
     /* QEMU can change multi-function devices to single function, or reverse */
     vdev->emulated_config_bits[PCI_HEADER_TYPE] =
                                               PCI_HEADER_TYPE_MULTI_FUNCTION;
@@ -3257,6 +3270,12 @@ bool vfio_pci_config_setup(VFIOPCIDevice *vdev, Error **errp)
 
     vfio_bars_register(vdev);
 
+    if (vdev->vga && vfio_is_vga(vdev)) {
+        pci_register_vga(&vdev->pdev, &vdev->vga->region[QEMU_PCI_VGA_MEM].mem,
+                         &vdev->vga->region[QEMU_PCI_VGA_IO_LO].mem,
+                         &vdev->vga->region[QEMU_PCI_VGA_IO_HI].mem);
+    }
+
     return true;
 }
 
@@ -3643,6 +3662,8 @@ 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 495fae7..4aa6461 100644
--- a/hw/vfio/pci.h
+++ b/hw/vfio/pci.h
@@ -157,6 +157,7 @@ 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)
@@ -205,10 +206,7 @@ static inline bool vfio_pci_is(VFIOPCIDevice *vdev, uint32_t vendor, uint32_t de
 
 static inline bool vfio_is_vga(VFIOPCIDevice *vdev)
 {
-    PCIDevice *pdev = &vdev->pdev;
-    uint16_t class = pci_get_word(pdev->config + PCI_CLASS_DEVICE);
-
-    return class == PCI_CLASS_DISPLAY_VGA;
+    return (vdev->class_code >> 8) == PCI_CLASS_DISPLAY_VGA;
 }
 
 /* MSI/MSI-X/INTx */
diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events
index 8ec0ad0..fc6ed23 100644
--- a/hw/vfio/trace-events
+++ b/hw/vfio/trace-events
@@ -48,6 +48,7 @@ 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"