[PATCH v3 7/7] vfio/igd: correctly calculate stolen memory size for gen 9 and later

[Corvin Köhne]

We have to update the calculation of the stolen memory size because
we've seen devices using values of 0xf0 and above for the graphics mode
select field. The new calculation was taken from the linux kernel [1].

[1] 
https://github.com/torvalds/linux/blob/7c626ce4bae1ac14f60076d00eafe71af30450ba/arch/x86/kernel/early-quirks.c#L455-L460

Signed-off-by: Corvin Köhne <c.koehne@beckhoff.com>
---
 hw/vfio/igd.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/hw/vfio/igd.c b/hw/vfio/igd.c
index 0751c43eae..a95d441f68 100644
--- a/hw/vfio/igd.c
+++ b/hw/vfio/igd.c
@@ -488,11 +488,18 @@ static int igd_get_stolen_mb(int gen, uint32_t gmch)
         gms = (gmch >> 8) & 0xff;
     }
 
-    if (gms > 0x10) {
-        error_report("Unsupported IGD GMS value 0x%x", gms);
-        return 0;
+    if (gen < 9) {
+        if (gms > 0x10) {
+            error_report("Unsupported IGD GMS value 0x%x", gms);
+            return 0;
+        }
+        return gms * 32;
+    } else {
+        if (gms < 0xf0)
+            return gms * 32;
+        else
+            return gms * 4 + 4;
     }
-    return gms * 32;
 }
 
 void vfio_probe_igd_bar4_quirk(VFIOPCIDevice *vdev, int nr)
-- 
2.46.0