vfio/igd: fix GTT stolen memory size calculation for gen 8+

On gen 8 and later devices, the GTT stolen memory size when GGMS equals
0 is 0 (no preallocated memory) rather than 1MB [1].

[1] 3.1.13, 5th Generation Intel Core Processor Family Datasheet Vol. 2
    https://www.intel.com/content/www/us/en/content-details/330835

Fixes: c4c45e943e51 ("vfio/pci: Intel graphics legacy mode assignment")
Reported-By: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Tomita Moeko <tomitamoeko@gmail.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Link: https://lore.kernel.org/r/20241206122749.9893-2-tomitamoeko@gmail.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>

diff --git a/hw/vfio/igd.c b/hw/vfio/igd.c
index 4047f4f0717f82f48f8e255873f9895a157e210a..73ed1ec8e6af60ed58fe6546f750d07fc972193e 100644 (file)
--- a/hw/vfio/igd.c
+++ b/hw/vfio/igd.c
@@ -268,7 +268,7 @@ static int vfio_igd_gtt_max(VFIOPCIDevice *vdev)
 
     gmch = vfio_pci_read_config(&vdev->pdev, IGD_GMCH, sizeof(gmch));
     ggms = (gmch >> (gen < 8 ? 8 : 6)) & 0x3;
-    if (gen > 6) {
+    if (gen > 6 && ggms != 0) {
         ggms = 1 << ggms;
     }
 
@@ -678,7 +678,7 @@ void vfio_probe_igd_bar4_quirk(VFIOPCIDevice *vdev, int nr)
 
     /* Determine the size of stolen memory needed for GTT */
     ggms_mb = (gmch >> (gen < 8 ? 8 : 6)) & 0x3;
-    if (gen > 6) {
+    if (gen > 6 && ggms_mb != 0) {
         ggms_mb = 1 << ggms_mb;
     }