[PULL 10/28] vfio/igd: Allow overriding GMS with 0xf0 to 0xfe on Gen9+

["Cédric Le Goater" <clg@redhat.com>]

From: Tomita Moeko <tomitamoeko@gmail.com>

On Gen9 and later IGD devices, GMS 0xf0 to 0xfe represents 4MB to 60MB
pre-allocated memory size in 4MB increments. Allow users overriding
GMS with these values.

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/20250505170305.23622-8-tomitamoeko@gmail.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>
---
 hw/vfio/igd.c | 59 +++++++++++++++++++++++++++++++++++----------------
 1 file changed, 41 insertions(+), 18 deletions(-)

diff --git a/hw/vfio/igd.c b/hw/vfio/igd.c
index 9dec32818c91f2021f6dc0c4bbe1fc0682df1a55..8ad9d723e29cd4d63e12346b6e40604ac020e747 100644
--- a/hw/vfio/igd.c
+++ b/hw/vfio/igd.c
@@ -412,6 +412,44 @@ static bool vfio_pci_igd_setup_lpc_bridge(VFIOPCIDevice *vdev, Error **errp)
     return true;
 }
 
+static bool vfio_pci_igd_override_gms(int gen, uint32_t gms, uint32_t *gmch)
+{
+    bool ret = false;
+
+    if (gen == -1) {
+        error_report("x-igd-gms is not supported on this device");
+    } else if (gen < 8) {
+        if (gms <= 0x10) {
+            *gmch &= ~(IGD_GMCH_GEN6_GMS_MASK << IGD_GMCH_GEN6_GMS_SHIFT);
+            *gmch |= gms << IGD_GMCH_GEN6_GMS_SHIFT;
+            ret = true;
+        } else {
+            error_report(QERR_INVALID_PARAMETER_VALUE, "x-igd-gms", "0~0x10");
+        }
+    } else if (gen == 8) {
+        if (gms <= 0x40) {
+            *gmch &= ~(IGD_GMCH_GEN8_GMS_MASK << IGD_GMCH_GEN8_GMS_SHIFT);
+            *gmch |= gms << IGD_GMCH_GEN8_GMS_SHIFT;
+            ret = true;
+        } else {
+            error_report(QERR_INVALID_PARAMETER_VALUE, "x-igd-gms", "0~0x40");
+        }
+    } else {
+        /* 0x0  to 0x40: 32MB increments starting at 0MB */
+        /* 0xf0 to 0xfe: 4MB increments starting at 4MB */
+        if ((gms <= 0x40) || (gms >= 0xf0 && gms <= 0xfe)) {
+            *gmch &= ~(IGD_GMCH_GEN8_GMS_MASK << IGD_GMCH_GEN8_GMS_SHIFT);
+            *gmch |= gms << IGD_GMCH_GEN8_GMS_SHIFT;
+            ret = true;
+        } else {
+            error_report(QERR_INVALID_PARAMETER_VALUE,
+                         "x-igd-gms", "0~0x40 or 0xf0~0xfe");
+        }
+    }
+
+    return ret;
+}
+
 #define IGD_GGC_MMIO_OFFSET     0x108040
 #define IGD_BDSM_MMIO_OFFSET    0x1080C0
 
@@ -594,24 +632,9 @@ 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) {
-        if (gen < 8) {
-            if (vdev->igd_gms <= 0x10) {
-                gmch &= ~(IGD_GMCH_GEN6_GMS_MASK << IGD_GMCH_GEN6_GMS_SHIFT);
-                gmch |= vdev->igd_gms << IGD_GMCH_GEN6_GMS_SHIFT;
-            } else {
-                error_report(QERR_INVALID_PARAMETER_VALUE,
-                             "x-igd-gms", "0~0x10");
-            }
-        } else {
-            if (vdev->igd_gms <= 0x40) {
-                gmch &= ~(IGD_GMCH_GEN8_GMS_MASK << IGD_GMCH_GEN8_GMS_SHIFT);
-                gmch |= vdev->igd_gms << IGD_GMCH_GEN8_GMS_SHIFT;
-            } else {
-                error_report(QERR_INVALID_PARAMETER_VALUE,
-                             "x-igd-gms", "0~0x40");
-            }
-        }
+    if (vdev->igd_gms &&
+        !vfio_pci_igd_override_gms(gen, vdev->igd_gms, &gmch)) {
+        return false;
     }
 
     gms_size = igd_stolen_memory_size(gen, gmch);
-- 
2.49.0