Introduce Virtio-loopback epsilon release:

Epsilon release introduces a new compatibility layer which make virtio-loopback
design to work with QEMU and rust-vmm vhost-user backend without require any
changes.

Signed-off-by: Timos Ampelikiotis <t.ampelikiotis@virtualopensystems.com>
Change-Id: I52e57563e08a7d0bdc002f8e928ee61ba0c53dd9

1 files changed, 616 insertions, 0 deletions

diff --git a/hw/vfio/igd.c b/hw/vfio/igd.c
new file mode 100644
index 000000000..d4685709a
--- /dev/null
+++ b/hw/vfio/igd.c
@@ -0,0 +1,616 @@
+/*
+ * IGD device quirks
+ *
+ * Copyright Red Hat, Inc. 2016
+ *
+ * Authors:
+ *  Alex Williamson <alex.williamson@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/units.h"
+#include "qapi/error.h"
+#include "hw/hw.h"
+#include "hw/nvram/fw_cfg.h"
+#include "pci.h"
+#include "trace.h"
+
+/*
+ * Intel IGD support
+ *
+ * Obviously IGD is not a discrete device, this is evidenced not only by it
+ * being integrated into the CPU, but by the various chipset and BIOS
+ * dependencies that it brings along with it.  Intel is trying to move away
+ * from this and Broadwell and newer devices can run in what Intel calls
+ * "Universal Pass-Through" mode, or UPT.  Theoretically in UPT mode, nothing
+ * more is required beyond assigning the IGD device to a VM.  There are
+ * however support limitations to this mode.  It only supports IGD as a
+ * secondary graphics device in the VM and it doesn't officially support any
+ * physical outputs.
+ *
+ * The code here attempts to enable what we'll call legacy mode assignment,
+ * IGD retains most of the capabilities we expect for it to have on bare
+ * metal.  To enable this mode, the IGD device must be assigned to the VM
+ * at PCI address 00:02.0, it must have a ROM, it very likely needs VGA
+ * support, we must have VM BIOS support for reserving and populating some
+ * of the required tables, and we need to tweak the chipset with revisions
+ * and IDs and an LPC/ISA bridge device.  The intention is to make all of
+ * this happen automatically by installing the device at the correct VM PCI
+ * bus address.  If any of the conditions are not met, we cross our fingers
+ * and hope the user knows better.
+ *
+ * NB - It is possible to enable physical outputs in UPT mode by supplying
+ * an OpRegion table.  We don't do this by default because the guest driver
+ * behaves differently if an OpRegion is provided and no monitor is attached
+ * vs no OpRegion and a monitor being attached or not.  Effectively, if a
+ * headless setup is desired, the OpRegion gets in the way of that.
+ */
+
+/*
+ * This presumes the device is already known to be an Intel VGA device, so we
+ * take liberties in which device ID bits match which generation.  This should
+ * not be taken as an indication that all the devices are supported, or even
+ * supportable, some of them don't even support VT-d.
+ * See linux:include/drm/i915_pciids.h for IDs.
+ */
+static int igd_gen(VFIOPCIDevice *vdev)
+{
+    if ((vdev->device_id & 0xfff) == 0xa84) {
+        return 8; /* Broxton */
+    }
+
+    switch (vdev->device_id & 0xff00) {
+    /* Old, untested, unavailable, unknown */
+    case 0x0000:
+    case 0x2500:
+    case 0x2700:
+    case 0x2900:
+    case 0x2a00:
+    case 0x2e00:
+    case 0x3500:
+    case 0xa000:
+        return -1;
+    /* SandyBridge, IvyBridge, ValleyView, Haswell */
+    case 0x0100:
+    case 0x0400:
+    case 0x0a00:
+    case 0x0c00:
+    case 0x0d00:
+    case 0x0f00:
+        return 6;
+    /* BroadWell, CherryView, SkyLake, KabyLake */
+    case 0x1600:
+    case 0x1900:
+    case 0x2200:
+    case 0x5900:
+        return 8;
+    }
+
+    return 8; /* Assume newer is compatible */
+}
+
+typedef struct VFIOIGDQuirk {
+    struct VFIOPCIDevice *vdev;
+    uint32_t index;
+    uint32_t bdsm;
+} VFIOIGDQuirk;
+
+#define IGD_GMCH 0x50 /* Graphics Control Register */
+#define IGD_BDSM 0x5c /* Base Data of Stolen Memory */
+
+
+/*
+ * The rather short list of registers that we copy from the host devices.
+ * The LPC/ISA bridge values are definitely needed to support the vBIOS, the
+ * host bridge values may or may not be needed depending on the guest OS.
+ * Since we're only munging revision and subsystem values on the host bridge,
+ * we don't require our own device.  The LPC/ISA bridge needs to be our very
+ * own though.
+ */
+typedef struct {
+    uint8_t offset;
+    uint8_t len;
+} IGDHostInfo;
+
+static const IGDHostInfo igd_host_bridge_infos[] = {
+    {PCI_REVISION_ID,         2},
+    {PCI_SUBSYSTEM_VENDOR_ID, 2},
+    {PCI_SUBSYSTEM_ID,        2},
+};
+
+static const IGDHostInfo igd_lpc_bridge_infos[] = {
+    {PCI_VENDOR_ID,           2},
+    {PCI_DEVICE_ID,           2},
+    {PCI_REVISION_ID,         2},
+    {PCI_SUBSYSTEM_VENDOR_ID, 2},
+    {PCI_SUBSYSTEM_ID,        2},
+};
+
+static int vfio_pci_igd_copy(VFIOPCIDevice *vdev, PCIDevice *pdev,
+                             struct vfio_region_info *info,
+                             const IGDHostInfo *list, int len)
+{
+    int i, ret;
+
+    for (i = 0; i < len; i++) {
+        ret = pread(vdev->vbasedev.fd, pdev->config + list[i].offset,
+                    list[i].len, info->offset + list[i].offset);
+        if (ret != list[i].len) {
+            error_report("IGD copy failed: %m");
+            return -errno;
+        }
+    }
+
+    return 0;
+}
+
+/*
+ * Stuff a few values into the host bridge.
+ */
+static int vfio_pci_igd_host_init(VFIOPCIDevice *vdev,
+                                  struct vfio_region_info *info)
+{
+    PCIBus *bus;
+    PCIDevice *host_bridge;
+    int ret;
+
+    bus = pci_device_root_bus(&vdev->pdev);
+    host_bridge = pci_find_device(bus, 0, PCI_DEVFN(0, 0));
+
+    if (!host_bridge) {
+        error_report("Can't find host bridge");
+        return -ENODEV;
+    }
+
+    ret = vfio_pci_igd_copy(vdev, host_bridge, info, igd_host_bridge_infos,
+                            ARRAY_SIZE(igd_host_bridge_infos));
+    if (!ret) {
+        trace_vfio_pci_igd_host_bridge_enabled(vdev->vbasedev.name);
+    }
+
+    return ret;
+}
+
+/*
+ * IGD LPC/ISA bridge support code.  The vBIOS needs this, but we can't write
+ * arbitrary values into just any bridge, so we must create our own.  We try
+ * to handle if the user has created it for us, which they might want to do
+ * to enable multifunction so we don't occupy the whole PCI slot.
+ */
+static void vfio_pci_igd_lpc_bridge_realize(PCIDevice *pdev, Error **errp)
+{
+    if (pdev->devfn != PCI_DEVFN(0x1f, 0)) {
+        error_setg(errp, "VFIO dummy ISA/LPC bridge must have address 1f.0");
+    }
+}
+
+static void vfio_pci_igd_lpc_bridge_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+    PCIDeviceClass *k = PCI_DEVICE_CLASS(klass);
+
+    set_bit(DEVICE_CATEGORY_BRIDGE, dc->categories);
+    dc->desc = "VFIO dummy ISA/LPC bridge for IGD assignment";
+    dc->hotpluggable = false;
+    k->realize = vfio_pci_igd_lpc_bridge_realize;
+    k->class_id = PCI_CLASS_BRIDGE_ISA;
+}
+
+static TypeInfo vfio_pci_igd_lpc_bridge_info = {
+    .name = "vfio-pci-igd-lpc-bridge",
+    .parent = TYPE_PCI_DEVICE,
+    .class_init = vfio_pci_igd_lpc_bridge_class_init,
+    .interfaces = (InterfaceInfo[]) {
+        { INTERFACE_CONVENTIONAL_PCI_DEVICE },
+        { },
+    },
+};
+
+static void vfio_pci_igd_register_types(void)
+{
+    type_register_static(&vfio_pci_igd_lpc_bridge_info);
+}
+
+type_init(vfio_pci_igd_register_types)
+
+static int vfio_pci_igd_lpc_init(VFIOPCIDevice *vdev,
+                                 struct vfio_region_info *info)
+{
+    PCIDevice *lpc_bridge;
+    int ret;
+
+    lpc_bridge = pci_find_device(pci_device_root_bus(&vdev->pdev),
+                                 0, PCI_DEVFN(0x1f, 0));
+    if (!lpc_bridge) {
+        lpc_bridge = pci_create_simple(pci_device_root_bus(&vdev->pdev),
+                                 PCI_DEVFN(0x1f, 0), "vfio-pci-igd-lpc-bridge");
+    }
+
+    ret = vfio_pci_igd_copy(vdev, lpc_bridge, info, igd_lpc_bridge_infos,
+                            ARRAY_SIZE(igd_lpc_bridge_infos));
+    if (!ret) {
+        trace_vfio_pci_igd_lpc_bridge_enabled(vdev->vbasedev.name);
+    }
+
+    return ret;
+}
+
+/*
+ * IGD Gen8 and newer support up to 8MB for the GTT and use a 64bit PTE
+ * entry, older IGDs use 2MB and 32bit.  Each PTE maps a 4k page.  Therefore
+ * we either have 2M/4k * 4 = 2k or 8M/4k * 8 = 16k as the maximum iobar index
+ * for programming the GTT.
+ *
+ * See linux:include/drm/i915_drm.h for shift and mask values.
+ */
+static int vfio_igd_gtt_max(VFIOPCIDevice *vdev)
+{
+    uint32_t gmch = vfio_pci_read_config(&vdev->pdev, IGD_GMCH, sizeof(gmch));
+    int ggms, gen = igd_gen(vdev);
+
+    gmch = vfio_pci_read_config(&vdev->pdev, IGD_GMCH, sizeof(gmch));
+    ggms = (gmch >> (gen < 8 ? 8 : 6)) & 0x3;
+    if (gen > 6) {
+        ggms = 1 << ggms;
+    }
+
+    ggms *= MiB;
+
+    return (ggms / (4 * KiB)) * (gen < 8 ? 4 : 8);
+}
+
+/*
+ * The IGD ROM will make use of stolen memory (GGMS) for support of VESA modes.
+ * Somehow the host stolen memory range is used for this, but how the ROM gets
+ * it is a mystery, perhaps it's hardcoded into the ROM.  Thankfully though, it
+ * reprograms the GTT through the IOBAR where we can trap it and transpose the
+ * programming to the VM allocated buffer.  That buffer gets reserved by the VM
+ * firmware via the fw_cfg entry added below.  Here we're just monitoring the
+ * IOBAR address and data registers to detect a write sequence targeting the
+ * GTTADR.  This code is developed by observed behavior and doesn't have a
+ * direct spec reference, unfortunately.
+ */
+static uint64_t vfio_igd_quirk_data_read(void *opaque,
+                                         hwaddr addr, unsigned size)
+{
+    VFIOIGDQuirk *igd = opaque;
+    VFIOPCIDevice *vdev = igd->vdev;
+
+    igd->index = ~0;
+
+    return vfio_region_read(&vdev->bars[4].region, addr + 4, size);
+}
+
+static void vfio_igd_quirk_data_write(void *opaque, hwaddr addr,
+                                      uint64_t data, unsigned size)
+{
+    VFIOIGDQuirk *igd = opaque;
+    VFIOPCIDevice *vdev = igd->vdev;
+    uint64_t val = data;
+    int gen = igd_gen(vdev);
+
+    /*
+     * Programming the GGMS starts at index 0x1 and uses every 4th index (ie.
+     * 0x1, 0x5, 0x9, 0xd,...).  For pre-Gen8 each 4-byte write is a whole PTE
+     * entry, with 0th bit enable set.  For Gen8 and up, PTEs are 64bit, so
+     * entries 0x5 & 0xd are the high dword, in our case zero.  Each PTE points
+     * to a 4k page, which we translate to a page from the VM allocated region,
+     * pointed to by the BDSM register.  If this is not set, we fail.
+     *
+     * We trap writes to the full configured GTT size, but we typically only
+     * see the vBIOS writing up to (nearly) the 1MB barrier.  In fact it often
+     * seems to miss the last entry for an even 1MB GTT.  Doing a gratuitous
+     * write of that last entry does work, but is hopefully unnecessary since
+     * we clear the previous GTT on initialization.
+     */
+    if ((igd->index % 4 == 1) && igd->index < vfio_igd_gtt_max(vdev)) {
+        if (gen < 8 || (igd->index % 8 == 1)) {
+            uint32_t base;
+
+            base = pci_get_long(vdev->pdev.config + IGD_BDSM);
+            if (!base) {
+                hw_error("vfio-igd: Guest attempted to program IGD GTT before "
+                         "BIOS reserved stolen memory.  Unsupported BIOS?");
+            }
+
+            val = data - igd->bdsm + base;
+        } else {
+            val = 0; /* upper 32bits of pte, we only enable below 4G PTEs */
+        }
+
+        trace_vfio_pci_igd_bar4_write(vdev->vbasedev.name,
+                                      igd->index, data, val);
+    }
+
+    vfio_region_write(&vdev->bars[4].region, addr + 4, val, size);
+
+    igd->index = ~0;
+}
+
+static const MemoryRegionOps vfio_igd_data_quirk = {
+    .read = vfio_igd_quirk_data_read,
+    .write = vfio_igd_quirk_data_write,
+    .endianness = DEVICE_LITTLE_ENDIAN,
+};
+
+static uint64_t vfio_igd_quirk_index_read(void *opaque,
+                                          hwaddr addr, unsigned size)
+{
+    VFIOIGDQuirk *igd = opaque;
+    VFIOPCIDevice *vdev = igd->vdev;
+
+    igd->index = ~0;
+
+    return vfio_region_read(&vdev->bars[4].region, addr, size);
+}
+
+static void vfio_igd_quirk_index_write(void *opaque, hwaddr addr,
+                                       uint64_t data, unsigned size)
+{
+    VFIOIGDQuirk *igd = opaque;
+    VFIOPCIDevice *vdev = igd->vdev;
+
+    igd->index = data;
+
+    vfio_region_write(&vdev->bars[4].region, addr, data, size);
+}
+
+static const MemoryRegionOps vfio_igd_index_quirk = {
+    .read = vfio_igd_quirk_index_read,
+    .write = vfio_igd_quirk_index_write,
+    .endianness = DEVICE_LITTLE_ENDIAN,
+};
+
+void vfio_probe_igd_bar4_quirk(VFIOPCIDevice *vdev, int nr)
+{
+    struct vfio_region_info *rom = NULL, *opregion = NULL,
+                            *host = NULL, *lpc = NULL;
+    VFIOQuirk *quirk;
+    VFIOIGDQuirk *igd;
+    PCIDevice *lpc_bridge;
+    int i, ret, ggms_mb, gms_mb = 0, gen;
+    uint64_t *bdsm_size;
+    uint32_t gmch;
+    uint16_t cmd_orig, cmd;
+    Error *err = NULL;
+
+    /*
+     * 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 ||
+        &vdev->pdev != pci_find_device(pci_device_root_bus(&vdev->pdev),
+                                       0, PCI_DEVFN(0x2, 0))) {
+        return;
+    }
+
+    /*
+     * We need to create an LPC/ISA bridge at PCI bus address 00:1f.0 that we
+     * can stuff host values into, so if there's already one there and it's not
+     * one we can hack on, legacy mode is no-go.  Sorry Q35.
+     */
+    lpc_bridge = pci_find_device(pci_device_root_bus(&vdev->pdev),
+                                 0, PCI_DEVFN(0x1f, 0));
+    if (lpc_bridge && !object_dynamic_cast(OBJECT(lpc_bridge),
+                                           "vfio-pci-igd-lpc-bridge")) {
+        error_report("IGD device %s cannot support legacy mode due to existing "
+                     "devices at address 1f.0", vdev->vbasedev.name);
+        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.
+     * NB. We only seem to get BIOS ROMs, so a UEFI VM would need CSM support.
+     */
+    ret = vfio_get_region_info(&vdev->vbasedev,
+                               VFIO_PCI_ROM_REGION_INDEX, &rom);
+    if ((ret || !rom->size) && !vdev->pdev.romfile) {
+        error_report("IGD device %s has no ROM, legacy mode disabled",
+                     vdev->vbasedev.name);
+        goto out;
+    }
+
+    /*
+     * Ignore the hotplug corner case, mark the ROM failed, we can't
+     * create the devices we need for legacy mode in the hotplug scenario.
+     */
+    if (vdev->pdev.qdev.hotplugged) {
+        error_report("IGD device %s hotplugged, ROM disabled, "
+                     "legacy mode disabled", vdev->vbasedev.name);
+        vdev->rom_read_failed = true;
+        goto out;
+    }
+
+    /*
+     * Check whether we have all the vfio device specific regions to
+     * support legacy mode (added in Linux v4.6).  If not, bail.
+     */
+    ret = vfio_get_dev_region_info(&vdev->vbasedev,
+                        VFIO_REGION_TYPE_PCI_VENDOR_TYPE | PCI_VENDOR_ID_INTEL,
+                        VFIO_REGION_SUBTYPE_INTEL_IGD_OPREGION, &opregion);
+    if (ret) {
+        error_report("IGD device %s does not support OpRegion access,"
+                     "legacy mode disabled", vdev->vbasedev.name);
+        goto out;
+    }
+
+    ret = vfio_get_dev_region_info(&vdev->vbasedev,
+                        VFIO_REGION_TYPE_PCI_VENDOR_TYPE | PCI_VENDOR_ID_INTEL,
+                        VFIO_REGION_SUBTYPE_INTEL_IGD_HOST_CFG, &host);
+    if (ret) {
+        error_report("IGD device %s does not support host bridge access,"
+                     "legacy mode disabled", vdev->vbasedev.name);
+        goto out;
+    }
+
+    ret = vfio_get_dev_region_info(&vdev->vbasedev,
+                        VFIO_REGION_TYPE_PCI_VENDOR_TYPE | PCI_VENDOR_ID_INTEL,
+                        VFIO_REGION_SUBTYPE_INTEL_IGD_LPC_CFG, &lpc);
+    if (ret) {
+        error_report("IGD device %s does not support LPC bridge access,"
+                     "legacy mode disabled", vdev->vbasedev.name);
+        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,
+     * but also no point in us enabling VGA if disabled in hardware.
+     */
+    if (!(gmch & 0x2) && !vdev->vga && vfio_populate_vga(vdev, &err)) {
+        error_reportf_err(err, VFIO_MSG_PREFIX, vdev->vbasedev.name);
+        error_report("IGD device %s failed to enable VGA access, "
+                     "legacy mode disabled", vdev->vbasedev.name);
+        goto out;
+    }
+
+    /* Create our LPC/ISA bridge */
+    ret = vfio_pci_igd_lpc_init(vdev, lpc);
+    if (ret) {
+        error_report("IGD device %s failed to create LPC bridge, "
+                     "legacy mode disabled", vdev->vbasedev.name);
+        goto out;
+    }
+
+    /* Stuff some host values into the VM PCI host bridge */
+    ret = vfio_pci_igd_host_init(vdev, host);
+    if (ret) {
+        error_report("IGD device %s failed to modify host bridge, "
+                     "legacy mode disabled", vdev->vbasedev.name);
+        goto out;
+    }
+
+    /* Setup OpRegion access */
+    ret = vfio_pci_igd_opregion_init(vdev, opregion, &err);
+    if (ret) {
+        error_append_hint(&err, "IGD legacy mode disabled\n");
+        error_reportf_err(err, VFIO_MSG_PREFIX, vdev->vbasedev.name);
+        goto out;
+    }
+
+    /* Setup our quirk to munge GTT addresses to the VM allocated buffer */
+    quirk = vfio_quirk_alloc(2);
+    igd = quirk->data = g_malloc0(sizeof(*igd));
+    igd->vdev = vdev;
+    igd->index = ~0;
+    igd->bdsm = vfio_pci_read_config(&vdev->pdev, IGD_BDSM, 4);
+    igd->bdsm &= ~((1 * MiB) - 1); /* 1MB aligned */
+
+    memory_region_init_io(&quirk->mem[0], OBJECT(vdev), &vfio_igd_index_quirk,
+                          igd, "vfio-igd-index-quirk", 4);
+    memory_region_add_subregion_overlap(vdev->bars[nr].region.mem,
+                                        0, &quirk->mem[0], 1);
+
+    memory_region_init_io(&quirk->mem[1], OBJECT(vdev), &vfio_igd_data_quirk,
+                          igd, "vfio-igd-data-quirk", 4);
+    memory_region_add_subregion_overlap(vdev->bars[nr].region.mem,
+                                        4, &quirk->mem[1], 1);
+
+    QLIST_INSERT_HEAD(&vdev->bars[nr].quirks, quirk, next);
+
+    /* Determine the size of stolen memory needed for GTT */
+    ggms_mb = (gmch >> (gen < 8 ? 8 : 6)) & 0x3;
+    if (gen > 6) {
+        ggms_mb = 1 << ggms_mb;
+    }
+
+    /*
+     * Assume we have no GMS memory, but allow it to be overridden by device
+     * option (experimental).  The spec doesn't actually allow zero GMS when
+     * 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);
+        } else {
+            error_report("Unsupported IGD GMS value 0x%x", vdev->igd_gms);
+            vdev->igd_gms = 0;
+        }
+    }
+
+    /*
+     * Request reserved memory for stolen memory via fw_cfg.  VM firmware
+     * must allocate a 1MB aligned reserved memory region below 4GB with
+     * the requested size (in bytes) for use by the Intel PCI class VGA
+     * device at VM address 00:02.0.  The base address of this reserved
+     * memory region must be written to the device BDSM register at PCI
+     * config offset 0x5C.
+     */
+    bdsm_size = g_malloc(sizeof(*bdsm_size));
+    *bdsm_size = cpu_to_le64((ggms_mb + gms_mb) * MiB);
+    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);
+    pci_set_long(vdev->emulated_config_bits + IGD_BDSM, ~0);
+
+    /*
+     * This IOBAR gives us access to GTTADR, which allows us to write to
+     * the GTT itself.  So let's go ahead and write zero to all the GTT
+     * entries to avoid spurious DMA faults.  Be sure I/O access is enabled
+     * before talking to the device.
+     */
+    if (pread(vdev->vbasedev.fd, &cmd_orig, sizeof(cmd_orig),
+              vdev->config_offset + PCI_COMMAND) != sizeof(cmd_orig)) {
+        error_report("IGD device %s - failed to read PCI command register",
+                     vdev->vbasedev.name);
+    }
+
+    cmd = cmd_orig | PCI_COMMAND_IO;
+
+    if (pwrite(vdev->vbasedev.fd, &cmd, sizeof(cmd),
+               vdev->config_offset + PCI_COMMAND) != sizeof(cmd)) {
+        error_report("IGD device %s - failed to write PCI command register",
+                     vdev->vbasedev.name);
+    }
+
+    for (i = 1; i < vfio_igd_gtt_max(vdev); i += 4) {
+        vfio_region_write(&vdev->bars[4].region, 0, i, 4);
+        vfio_region_write(&vdev->bars[4].region, 4, 0, 4);
+    }
+
+    if (pwrite(vdev->vbasedev.fd, &cmd_orig, sizeof(cmd_orig),
+               vdev->config_offset + PCI_COMMAND) != sizeof(cmd_orig)) {
+        error_report("IGD device %s - failed to restore PCI command register",
+                     vdev->vbasedev.name);
+    }
+
+    trace_vfio_pci_igd_bdsm_enabled(vdev->vbasedev.name, ggms_mb + gms_mb);
+
+out:
+    g_free(rom);
+    g_free(opregion);
+    g_free(host);
+    g_free(lpc);
+}