Revert "vfio/pci-quirks.c: Disable stolen memory for igd VFIO"

This reverts commit c2b2e158cc.

The original patch intend to prevent linux i915 driver from using
stolen meory. But this patch breaks windows IGD driver loading on
Gen9+, as IGD HW will use stolen memory on Gen9+, once windows IGD
driver see zero size stolen memory, it will unload.
Meanwhile stolen memory will be disabled in 915 when i915 run as
a guest.

Signed-off-by: Xiong Zhang <xiong.y.zhang@intel.com>
[aw: Gen9+ is SkyLake and newer]
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

hw/vfio/pci-quirks.c

@@ -1367,45 +1367,14 @@ static void vfio_probe_igd_bar4_quirk(VFIOPCIDevice *vdev, int nr)
     uint16_t cmd_orig, cmd;
     Error *err = NULL;
 
-    /* This must be an Intel VGA device. */
+    /*
+     * This must be an Intel VGA device at address 00:02.0 for us to even
+     * consider enabling legacy mode.  The vBIOS has dependencies on the
+     * PCI bus address.
+     */
     if (!vfio_pci_is(vdev, PCI_VENDOR_ID_INTEL, PCI_ANY_ID) ||
-        !vfio_is_vga(vdev) || nr != 4) {
+        !vfio_is_vga(vdev) || nr != 4 ||
-        return;
+        &vdev->pdev != pci_find_device(pci_device_root_bus(&vdev->pdev),
-    }
-
-    /*
-     * IGD is not a standard, they like to change their specs often.  We
-     * only attempt to support back to SandBridge and we hope that newer
-     * devices maintain compatibility with generation 8.
-     */
-    gen = igd_gen(vdev);
-    if (gen != 6 && gen != 8) {
-        error_report("IGD device %s is unsupported by IGD quirks, "
-                     "try SandyBridge or newer", vdev->vbasedev.name);
-        return;
-    }
-
-    /*
-     * Regardless of running in UPT or legacy mode, the guest graphics
-     * driver may attempt to use stolen memory, however only legacy mode
-     * has BIOS support for reserving stolen memory in the guest VM.
-     * Emulate the GMCH register in all cases and zero out the stolen
-     * memory size here. Legacy mode may request allocation and re-write
-     * this below.
-     */
-    gmch = vfio_pci_read_config(&vdev->pdev, IGD_GMCH, 4);
-    gmch &= ~((gen < 8 ? 0x1f : 0xff) << (gen < 8 ? 3 : 8));
-
-    /* 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);
-
-    /*
-     * This must be at address 00:02.0 for us to even onsider enabling
-     * legacy mode.  The vBIOS has dependencies on the PCI bus address.
-     */
-    if (&vdev->pdev != pci_find_device(pci_device_root_bus(&vdev->pdev),
                                        0, PCI_DEVFN(0x2, 0))) {
         return;
     }
@@ -1424,6 +1393,18 @@ static void vfio_probe_igd_bar4_quirk(VFIOPCIDevice *vdev, int nr)
         return;
     }
 
+    /*
+     * IGD is not a standard, they like to change their specs often.  We
+     * only attempt to support back to SandBridge and we hope that newer
+     * devices maintain compatibility with generation 8.
+     */
+    gen = igd_gen(vdev);
+    if (gen != 6 && gen != 8) {
+        error_report("IGD device %s is unsupported in legacy mode, "
+                     "try SandyBridge or newer", vdev->vbasedev.name);
+        return;
+    }
+
     /*
      * Most of what we're doing here is to enable the ROM to run, so if
      * there's no ROM, there's no point in setting up this quirk.
@@ -1479,6 +1460,8 @@ static void vfio_probe_igd_bar4_quirk(VFIOPCIDevice *vdev, int nr)
         goto out;
     }
 
+    gmch = vfio_pci_read_config(&vdev->pdev, IGD_GMCH, 4);
+
     /*
      * If IGD VGA Disable is clear (expected) and VGA is not already enabled,
      * try to enable it.  Probably shouldn't be using legacy mode without VGA,
@@ -1549,11 +1532,12 @@ static void vfio_probe_igd_bar4_quirk(VFIOPCIDevice *vdev, int nr)
      * when IVD (IGD VGA Disable) is clear, but the claim is that it's unused,
      * so let's not waste VM memory for it.
      */
+    gmch &= ~((gen < 8 ? 0x1f : 0xff) << (gen < 8 ? 3 : 8));
+
     if (vdev->igd_gms) {
         if (vdev->igd_gms <= 0x10) {
             gms_mb = vdev->igd_gms * 32;
             gmch |= vdev->igd_gms << (gen < 8 ? 3 : 8);
-            pci_set_long(vdev->pdev.config + IGD_GMCH, gmch);
         } else {
             error_report("Unsupported IGD GMS value 0x%x", vdev->igd_gms);
             vdev->igd_gms = 0;
@@ -1573,6 +1557,11 @@ static void vfio_probe_igd_bar4_quirk(VFIOPCIDevice *vdev, int nr)
     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 */
     pci_set_long(vdev->pdev.config + IGD_BDSM, 0);
     pci_set_long(vdev->pdev.wmask + IGD_BDSM, ~0);