[PATCH] hw/igd: fix calculation of graphics stolen memory

[Corvin Köhne]

From: Corvin Köhne <c.koehne@beckhoff.com>

When copying the calculation of the stolen memory size for Intels integrated
graphics device of gen 9 and later from the Linux kernel [1], we missed
subtracting 0xf0 from the graphics mode select value for values above 0xf0.
This leads to QEMU reporting a very large size of the graphics stolen memory
area. That's just a waste of memory. Additionally the guest firmware might be
unable to allocate such a large buffer.

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

Fixes: 8719224166832ff8230d7dd8599f42bd60e2eb96
Signed-off-by: Corvin Köhne <c.koehne@beckhoff.com>
---
 hw/vfio/igd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/vfio/igd.c b/hw/vfio/igd.c
index a95d441f68..732f9c37a6 100644
--- a/hw/vfio/igd.c
+++ b/hw/vfio/igd.c
@@ -498,7 +498,7 @@ static int igd_get_stolen_mb(int gen, uint32_t gmch)
         if (gms < 0xf0)
             return gms * 32;
         else
-            return gms * 4 + 4;
+            return (gms - 0xf0) * 4 + 4;
     }
 }
 
-- 
2.47.0