vfio/igd: Only emulate GGC register when x-igd-gms is set

x-igd-gms is used for overriding DSM region size in GGC register in
both config space and MMIO BAR0, by default host value is used.
There is no need to emulate it in default case.

Signed-off-by: Tomita Moeko <tomitamoeko@gmail.com>
Reviewed-by: Corvin Köhne <c.koehne@beckhoff.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Tested-by: Alex Williamson <alex.williamson@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20250505170305.23622-9-tomitamoeko@gmail.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>

1 files changed, 26 insertions, 23 deletions

diff --git a/hw/vfio/igd.c b/hw/vfio/igd.c
index 8ad9d72..886d44f 100644
--- a/hw/vfio/igd.c
+++ b/hw/vfio/igd.c
@@ -478,22 +478,24 @@ void vfio_probe_igd_bar0_quirk(VFIOPCIDevice *vdev, int nr)
         return;
     }
 
-    ggc_quirk = vfio_quirk_alloc(1);
-    ggc_mirror = ggc_quirk->data = g_malloc0(sizeof(*ggc_mirror));
-    ggc_mirror->mem = ggc_quirk->mem;
-    ggc_mirror->vdev = vdev;
-    ggc_mirror->bar = nr;
-    ggc_mirror->offset = IGD_GGC_MMIO_OFFSET;
-    ggc_mirror->config_offset = IGD_GMCH;
-
-    memory_region_init_io(ggc_mirror->mem, OBJECT(vdev),
-                          &vfio_generic_mirror_quirk, ggc_mirror,
-                          "vfio-igd-ggc-quirk", 2);
-    memory_region_add_subregion_overlap(vdev->bars[nr].region.mem,
-                                        ggc_mirror->offset, ggc_mirror->mem,
-                                        1);
+    if (vdev->igd_gms) {
+        ggc_quirk = vfio_quirk_alloc(1);
+        ggc_mirror = ggc_quirk->data = g_malloc0(sizeof(*ggc_mirror));
+        ggc_mirror->mem = ggc_quirk->mem;
+        ggc_mirror->vdev = vdev;
+        ggc_mirror->bar = nr;
+        ggc_mirror->offset = IGD_GGC_MMIO_OFFSET;
+        ggc_mirror->config_offset = IGD_GMCH;
 
-    QLIST_INSERT_HEAD(&vdev->bars[nr].quirks, ggc_quirk, next);
+        memory_region_init_io(ggc_mirror->mem, OBJECT(vdev),
+                              &vfio_generic_mirror_quirk, ggc_mirror,
+                              "vfio-igd-ggc-quirk", 2);
+        memory_region_add_subregion_overlap(vdev->bars[nr].region.mem,
+                                            ggc_mirror->offset, ggc_mirror->mem,
+                                            1);
+
+        QLIST_INSERT_HEAD(&vdev->bars[nr].quirks, ggc_quirk, next);
+    }
 
     bdsm_quirk = vfio_quirk_alloc(1);
     bdsm_mirror = bdsm_quirk->data = g_malloc0(sizeof(*bdsm_mirror));
@@ -632,9 +634,15 @@ static bool vfio_pci_igd_config_quirk(VFIOPCIDevice *vdev, Error **errp)
      * 32MiB. This option should only be used when the desired size cannot be
      * set from DVMT Pre-Allocated option in host BIOS.
      */
-    if (vdev->igd_gms &&
-        !vfio_pci_igd_override_gms(gen, vdev->igd_gms, &gmch)) {
-        return false;
+    if (vdev->igd_gms) {
+        if (!vfio_pci_igd_override_gms(gen, vdev->igd_gms, &gmch)) {
+            return false;
+        }
+
+        /* GMCH is read-only, emulated */
+        pci_set_long(vdev->pdev.config + IGD_GMCH, gmch);
+        pci_set_long(vdev->pdev.wmask + IGD_GMCH, 0);
+        pci_set_long(vdev->emulated_config_bits + IGD_GMCH, ~0);
     }
 
     gms_size = igd_stolen_memory_size(gen, gmch);
@@ -652,11 +660,6 @@ static bool vfio_pci_igd_config_quirk(VFIOPCIDevice *vdev, Error **errp)
     fw_cfg_add_file(fw_cfg_find(), "etc/igd-bdsm-size",
                     bdsm_size, sizeof(*bdsm_size));
 
-    /* GMCH is read-only, emulated */
-    pci_set_long(vdev->pdev.config + IGD_GMCH, gmch);
-    pci_set_long(vdev->pdev.wmask + IGD_GMCH, 0);
-    pci_set_long(vdev->emulated_config_bits + IGD_GMCH, ~0);
-
     /* BDSM is read-write, emulated.  The BIOS needs to be able to write it */
     if (gen < 11) {
         pci_set_long(vdev->pdev.config + IGD_BDSM, 0);