Display device, demo-ing the vfio dmabuf display interface
(VFIO_GFX_PLANE_TYPE_DMABUF).  Compatible enough to qemu stdvga
that bochs-drm.ko can be used as guest driver.

Signed-off-by: Gerd Hoffmann <kra...@redhat.com>
---
 samples/vfio-mdev/mbochs.c | 1379 ++++++++++++++++++++++++++++++++++++++++++++
 samples/Kconfig            |   13 +
 samples/vfio-mdev/Makefile |    1 +
 3 files changed, 1393 insertions(+)
 create mode 100644 samples/vfio-mdev/mbochs.c

diff --git a/samples/vfio-mdev/mbochs.c b/samples/vfio-mdev/mbochs.c
new file mode 100644
index 0000000000..fc91523190
--- /dev/null
+++ b/samples/vfio-mdev/mbochs.c
@@ -0,0 +1,1379 @@
+/*
+ * Mediated virtual PCI display host device driver
+ *
+ * Emulate enough of qemu stdvga to make bochs-drm.ko happy.  That is
+ * basically the vram memory bar and the bochs dispi interface vbe
+ * registers in the mmio register bar. Specifically it does *not*
+ * include any legacy vga stuff.  Device looks alot like "qemu -device
+ * secondary-vga".
+ *
+ *   (c) Gerd Hoffmann <kra...@redhat.com>
+ *
+ * based on mtty driver which is:
+ *   Copyright (c) 2016, NVIDIA CORPORATION. All rights reserved.
+ *      Author: Neo Jia <c...@nvidia.com>
+ *              Kirti Wankhede <kwankh...@nvidia.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/cdev.h>
+#include <linux/vfio.h>
+#include <linux/iommu.h>
+#include <linux/sysfs.h>
+#include <linux/mdev.h>
+#include <linux/pci.h>
+#include <linux/dma-buf.h>
+#include <linux/highmem.h>
+#include <drm/drm_fourcc.h>
+#include <drm/drm_rect.h>
+#include <drm/drm_modeset_lock.h>
+#include <drm/drm_plane.h>
+
+
+#define VBE_DISPI_INDEX_ID             0x0
+#define VBE_DISPI_INDEX_XRES           0x1
+#define VBE_DISPI_INDEX_YRES           0x2
+#define VBE_DISPI_INDEX_BPP            0x3
+#define VBE_DISPI_INDEX_ENABLE         0x4
+#define VBE_DISPI_INDEX_BANK           0x5
+#define VBE_DISPI_INDEX_VIRT_WIDTH     0x6
+#define VBE_DISPI_INDEX_VIRT_HEIGHT    0x7
+#define VBE_DISPI_INDEX_X_OFFSET       0x8
+#define VBE_DISPI_INDEX_Y_OFFSET       0x9
+#define VBE_DISPI_INDEX_VIDEO_MEMORY_64K 0xa
+#define VBE_DISPI_INDEX_COUNT          0xb
+
+#define VBE_DISPI_ID0                  0xB0C0
+#define VBE_DISPI_ID1                  0xB0C1
+#define VBE_DISPI_ID2                  0xB0C2
+#define VBE_DISPI_ID3                  0xB0C3
+#define VBE_DISPI_ID4                  0xB0C4
+#define VBE_DISPI_ID5                  0xB0C5
+
+#define VBE_DISPI_DISABLED             0x00
+#define VBE_DISPI_ENABLED              0x01
+#define VBE_DISPI_GETCAPS              0x02
+#define VBE_DISPI_8BIT_DAC             0x20
+#define VBE_DISPI_LFB_ENABLED          0x40
+#define VBE_DISPI_NOCLEARMEM           0x80
+
+
+#define MBOCHS_NAME              "mbochs"
+#define MBOCHS_CLASS_NAME        "mbochs"
+
+#define MBOCHS_CONFIG_SPACE_SIZE  0xff
+#define MBOCHS_MMIO_BAR_OFFSET   PAGE_SIZE
+#define MBOCHS_MMIO_BAR_SIZE     PAGE_SIZE
+#define MBOCHS_MEMORY_BAR_OFFSET  (MBOCHS_MMIO_BAR_OFFSET + 
MBOCHS_MMIO_BAR_SIZE)
+
+#define STORE_LE16(addr, val)  (*(u16 *)addr = val)
+#define STORE_LE32(addr, val)  (*(u32 *)addr = val)
+
+
+MODULE_LICENSE("GPL v2");
+
+static int max_mbytes = 256;
+module_param_named(count, max_mbytes, int, 0444);
+MODULE_PARM_DESC(mem, "megabytes available to " MBOCHS_NAME " devices");
+
+
+#define MBOCHS_TYPE_1 "small"
+#define MBOCHS_TYPE_2 "medium"
+#define MBOCHS_TYPE_3 "large"
+
+static const struct mbochs_type {
+       const char *name;
+       u32 mbytes;
+} mbochs_types[] = {
+       {
+               .name   = MBOCHS_CLASS_NAME "-" MBOCHS_TYPE_1,
+               .mbytes = 4,
+       },{
+               .name   = MBOCHS_CLASS_NAME "-" MBOCHS_TYPE_2,
+               .mbytes = 16,
+       },{
+               .name   = MBOCHS_CLASS_NAME "-" MBOCHS_TYPE_3,
+               .mbytes = 64,
+       },
+};
+
+
+static dev_t           mbochs_devt;
+static struct class    *mbochs_class;
+static struct cdev     mbochs_cdev;
+static struct device   mbochs_dev;
+static int             mbochs_used_mbytes;
+
+struct mbochs_mode {
+       u32 drm_format;
+       u32 bytepp;
+       u32 width;
+       u32 height;
+       u32 stride;
+       u32 __pad;
+       u64 offset;
+       u64 size;
+};
+
+struct mbochs_dmabuf {
+       struct mbochs_mode mode;
+       u32 id;
+       struct page **pages;
+       pgoff_t pagecount;
+       struct dma_buf *buf;
+       struct mdev_state *mdev_state;
+       struct list_head next;
+       bool unlinked;
+};
+
+/* State of each mdev device */
+struct mdev_state {
+       u8 *vconfig;
+       u64 bar_mask[3];
+       u32 memory_bar_mask;
+       struct mutex ops_lock;
+       struct mdev_device *mdev;
+       struct vfio_device_info dev_info;
+
+       const struct mbochs_type *type;
+       u16 vbe[VBE_DISPI_INDEX_COUNT];
+       u64 memsize;
+       struct page **pages;
+       pgoff_t pagecount;
+
+       struct list_head dmabufs;
+       u32 active_id;
+       u32 next_id;
+};
+
+static const char *vbe_name_list[VBE_DISPI_INDEX_COUNT] = {
+       [ VBE_DISPI_INDEX_ID               ] = "id",
+       [ VBE_DISPI_INDEX_XRES             ] = "xres",
+       [ VBE_DISPI_INDEX_YRES             ] = "yres",
+       [ VBE_DISPI_INDEX_BPP              ] = "bpp",
+       [ VBE_DISPI_INDEX_ENABLE           ] = "enable",
+       [ VBE_DISPI_INDEX_BANK             ] = "bank",
+       [ VBE_DISPI_INDEX_VIRT_WIDTH       ] = "virt-width",
+       [ VBE_DISPI_INDEX_VIRT_HEIGHT      ] = "virt-height",
+       [ VBE_DISPI_INDEX_X_OFFSET         ] = "x-offset",
+       [ VBE_DISPI_INDEX_Y_OFFSET         ] = "y-offset",
+       [ VBE_DISPI_INDEX_VIDEO_MEMORY_64K ] = "video-mem",
+};
+
+static const char *vbe_name(u32 index)
+{
+       if (index < ARRAY_SIZE(vbe_name_list))
+               return vbe_name_list[index];
+       return "(invalid)";
+}
+
+static const struct mbochs_type *mbochs_find_type(struct kobject *kobj)
+{
+       int i;
+
+       for (i = 0; i < ARRAY_SIZE(mbochs_types); i++)
+               if (strcmp(mbochs_types[i].name, kobj->name) == 0)
+                       return mbochs_types + i;
+       return NULL;
+}
+
+static void mbochs_create_config_space(struct mdev_state *mdev_state)
+{
+       STORE_LE16((u16 *) &mdev_state->vconfig[PCI_VENDOR_ID],
+                  0x1234);
+       STORE_LE16((u16 *) &mdev_state->vconfig[PCI_DEVICE_ID],
+                  0x1111);
+       STORE_LE16((u16 *) &mdev_state->vconfig[PCI_SUBSYSTEM_VENDOR_ID],
+                  PCI_SUBVENDOR_ID_REDHAT_QUMRANET);
+       STORE_LE16((u16 *) &mdev_state->vconfig[PCI_SUBSYSTEM_ID],
+                  PCI_SUBDEVICE_ID_QEMU);
+
+       STORE_LE16((u16 *) &mdev_state->vconfig[PCI_COMMAND],
+                  PCI_COMMAND_IO | PCI_COMMAND_MEMORY);
+       STORE_LE16((u16 *) &mdev_state->vconfig[PCI_CLASS_DEVICE],
+                  PCI_CLASS_DISPLAY_OTHER);
+       mdev_state->vconfig[PCI_CLASS_REVISION] =  0x01;
+
+       STORE_LE32((u32 *) &mdev_state->vconfig[PCI_BASE_ADDRESS_0],
+                  PCI_BASE_ADDRESS_SPACE_MEMORY |
+                  PCI_BASE_ADDRESS_MEM_TYPE_32  |
+                  PCI_BASE_ADDRESS_MEM_PREFETCH);
+       mdev_state->bar_mask[0] = ~(mdev_state->memsize) + 1;
+
+       STORE_LE32((u32 *) &mdev_state->vconfig[PCI_BASE_ADDRESS_2],
+                  PCI_BASE_ADDRESS_SPACE_MEMORY |
+                  PCI_BASE_ADDRESS_MEM_TYPE_32);
+       mdev_state->bar_mask[2] = ~(MBOCHS_MMIO_BAR_SIZE) + 1;
+}
+
+static int mbochs_check_framebuffer(struct mdev_state *mdev_state,
+                                   struct mbochs_mode *mode)
+{
+       struct device *dev = mdev_dev(mdev_state->mdev);
+       u16 *vbe = mdev_state->vbe;
+       u32 virt_width;
+
+       WARN_ON(!mutex_is_locked(&mdev_state->ops_lock));
+
+       if (!(vbe[VBE_DISPI_INDEX_ENABLE] & VBE_DISPI_ENABLED))
+               goto nofb;
+
+       memset(mode, 0, sizeof(*mode));
+       switch (vbe[VBE_DISPI_INDEX_BPP]) {
+       case 32:
+               mode->drm_format = DRM_FORMAT_XRGB8888;
+               mode->bytepp = 4;
+               break;
+       default:
+               dev_info_ratelimited(dev, "%s: bpp %d not supported\n", 
__func__,
+                                    vbe[VBE_DISPI_INDEX_BPP]);
+               goto nofb;
+       }
+
+       mode->width  = vbe[VBE_DISPI_INDEX_XRES];
+       mode->height = vbe[VBE_DISPI_INDEX_YRES];
+       virt_width  = vbe[VBE_DISPI_INDEX_VIRT_WIDTH];
+       if (virt_width < mode->width)
+               virt_width = mode->width;
+       mode->stride = virt_width * mode->bytepp;
+       mode->size   = (u64)mode->stride * mode->height;
+       mode->offset = ((u64)vbe[VBE_DISPI_INDEX_X_OFFSET] * mode->bytepp +
+                      (u64)vbe[VBE_DISPI_INDEX_Y_OFFSET] * mode->stride);
+
+       if (mode->width < 64 || mode->height < 64) {
+               dev_info_ratelimited(dev, "%s: invalid resolution %dx%d\n",
+                                    __func__, mode->width, mode->height);
+               goto nofb;
+       }
+       if (mode->offset + mode->size > mdev_state->memsize) {
+               dev_info_ratelimited(dev, "%s: framebuffer memory overflow\n",
+                                    __func__);
+               goto nofb;
+       }
+
+       return 0;
+
+nofb:
+       memset(mode, 0, sizeof(*mode));
+       return -EINVAL;
+}
+
+static bool mbochs_modes_equal(struct mbochs_mode *mode1,
+                              struct mbochs_mode *mode2)
+{
+       return memcmp(mode1, mode2, sizeof(struct mbochs_mode)) == 0;
+}
+
+static void handle_pci_cfg_write(struct mdev_state *mdev_state, u16 offset,
+                                char *buf, u32 count)
+{
+       struct device *dev = mdev_dev(mdev_state->mdev);
+       int index = (offset - PCI_BASE_ADDRESS_0) / 0x04;
+       u32 cfg_addr;
+
+       switch (offset) {
+       case PCI_BASE_ADDRESS_0:
+       case PCI_BASE_ADDRESS_2:
+               cfg_addr = *(u32 *)buf;
+
+               if (cfg_addr == 0xffffffff) {
+                       cfg_addr = (cfg_addr & mdev_state->bar_mask[index]);
+               } else {
+                       cfg_addr &= PCI_BASE_ADDRESS_MEM_MASK;
+                       if (cfg_addr)
+                               dev_info(dev, "BAR #%d @ 0x%x\n",
+                                        index, cfg_addr);
+               }
+
+               cfg_addr |= (mdev_state->vconfig[offset] &
+                            ~PCI_BASE_ADDRESS_MEM_MASK);
+               STORE_LE32(&mdev_state->vconfig[offset], cfg_addr);
+               break;
+       }
+}
+
+static void handle_mmio_write(struct mdev_state *mdev_state, u16 offset,
+                             char *buf, u32 count)
+{
+       struct device *dev = mdev_dev(mdev_state->mdev);
+       int index;
+       u16 reg16;
+
+       switch (offset) {
+       case 0x400 ... 0x41f: /* vga ioports remapped */
+               goto unhandled;
+       case 0x500 ... 0x515: /* bochs dispi interface */
+               if (count != 2)
+                       goto unhandled;
+               index = (offset - 0x500) / 2;
+               reg16 = *(u16*)buf;
+               if (index < ARRAY_SIZE(mdev_state->vbe))
+                       mdev_state->vbe[index] = reg16;
+               dev_dbg(dev, "%s: vbe write %d = %d (%s)\n",
+                       __func__, index, reg16, vbe_name(index));
+               break;
+       case 0x600 ... 0x607: /* qemu extended regs */
+               goto unhandled;
+       default:
+       unhandled:
+               dev_dbg(dev, "%s: @0x%03x, count %d (unhandled)\n",
+                       __func__, offset, count);
+               break;
+       }
+}
+
+static void handle_mmio_read(struct mdev_state *mdev_state, u16 offset,
+                            char *buf, u32 count)
+{
+       struct device *dev = mdev_dev(mdev_state->mdev);
+       u16 reg16 = 0;
+       int index;
+
+       switch (offset) {
+       case 0x500 ... 0x515: /* bochs dispi interface */
+               if (count != 2)
+                       goto unhandled;
+               index = (offset - 0x500) / 2;
+               if (index < ARRAY_SIZE(mdev_state->vbe))
+                       reg16 = mdev_state->vbe[index];
+               dev_dbg(dev, "%s: vbe read %d = %d (%s)\n",
+                       __func__, index, reg16, vbe_name(index));
+               *(u16*)buf = reg16;
+               break;
+       default:
+       unhandled:
+               dev_dbg(dev, "%s: @0x%03x, count %d (unhandled)\n",
+                       __func__, offset, count);
+               memset(buf, 0, count);
+               break;
+       }
+}
+
+static ssize_t mdev_access(struct mdev_device *mdev, char *buf, size_t count,
+                          loff_t pos, bool is_write)
+{
+       struct mdev_state *mdev_state = mdev_get_drvdata(mdev);
+       struct device *dev = mdev_dev(mdev);
+       int ret = 0;
+
+       mutex_lock(&mdev_state->ops_lock);
+
+       if (pos < MBOCHS_CONFIG_SPACE_SIZE) {
+               if (is_write) {
+                       handle_pci_cfg_write(mdev_state, pos, buf, count);
+               } else {
+                       memcpy(buf, (mdev_state->vconfig + pos), count);
+               }
+
+       } else if (pos >= MBOCHS_MMIO_BAR_OFFSET &&
+                  pos + count <  MBOCHS_MEMORY_BAR_OFFSET) {
+               pos -= MBOCHS_MMIO_BAR_OFFSET;
+               if (is_write) {
+                       handle_mmio_write(mdev_state, pos, buf, count);
+               } else {
+                       handle_mmio_read(mdev_state, pos, buf, count);
+               }
+
+       } else {
+               dev_dbg(dev, "%s: %s @0x%llx (unhandled)\n",
+                       __func__, is_write ? "WR" : "RD", pos);
+               ret = -1;
+               goto accessfailed;
+       }
+
+       ret = count;
+
+
+accessfailed:
+       mutex_unlock(&mdev_state->ops_lock);
+
+       return ret;
+}
+
+int mbochs_reset(struct mdev_device *mdev)
+{
+       struct mdev_state *mdev_state = mdev_get_drvdata(mdev);
+       u32 size64k = mdev_state->memsize / (64 * 1024);
+       int i;
+
+       for (i = 0; i < ARRAY_SIZE(mdev_state->vbe); i++)
+               mdev_state->vbe[i] = 0;
+       mdev_state->vbe[VBE_DISPI_INDEX_ID] = VBE_DISPI_ID5;
+       mdev_state->vbe[VBE_DISPI_INDEX_VIDEO_MEMORY_64K] = size64k;
+       return 0;
+}
+
+int mbochs_create(struct kobject *kobj, struct mdev_device *mdev)
+{
+       const struct mbochs_type *type = mbochs_find_type(kobj);
+       struct device *dev = mdev_dev(mdev);
+       struct mdev_state *mdev_state;
+
+       if (!type)
+               type = &mbochs_types[0];
+       if (type->mbytes + mbochs_used_mbytes > max_mbytes)
+               return -ENOMEM;
+
+       mdev_state = kzalloc(sizeof(struct mdev_state), GFP_KERNEL);
+       if (mdev_state == NULL)
+               return -ENOMEM;
+
+       mdev_state->vconfig = kzalloc(MBOCHS_CONFIG_SPACE_SIZE, GFP_KERNEL);
+       if (mdev_state->vconfig == NULL)
+               goto err_mem;
+
+       mdev_state->memsize = type->mbytes * 1024 * 1024;
+       mdev_state->pagecount = mdev_state->memsize >> PAGE_SHIFT;
+       mdev_state->pages = kzalloc(mdev_state->pagecount * sizeof(struct 
page*),
+                                   GFP_KERNEL);
+       if (!mdev_state->pages)
+               goto err_mem;
+
+       dev_info(dev, "%s: %s, %d MB, %ld pages\n", __func__,
+                kobj->name, type->mbytes, mdev_state->pagecount);
+
+       mutex_init(&mdev_state->ops_lock);
+       mdev_state->mdev = mdev;
+       mdev_set_drvdata(mdev, mdev_state);
+       INIT_LIST_HEAD(&mdev_state->dmabufs);
+       mdev_state->next_id = 1;
+
+       mdev_state->type = type;
+       mbochs_create_config_space(mdev_state);
+       mbochs_reset(mdev);
+
+       mbochs_used_mbytes += type->mbytes;
+       return 0;
+
+err_mem:
+       kfree(mdev_state->vconfig);
+       kfree(mdev_state);
+       return -ENOMEM;
+}
+
+int mbochs_remove(struct mdev_device *mdev)
+{
+       struct mdev_state *mdev_state = mdev_get_drvdata(mdev);
+
+       mbochs_used_mbytes -= mdev_state->type->mbytes;
+       mdev_set_drvdata(mdev, NULL);
+       kfree(mdev_state->pages);
+       kfree(mdev_state->vconfig);
+       kfree(mdev_state);
+       return 0;
+}
+
+ssize_t mbochs_read(struct mdev_device *mdev, char __user *buf,
+                   size_t count, loff_t *ppos)
+{
+       unsigned int done = 0;
+       int ret;
+
+       while (count) {
+               size_t filled;
+
+               if (count >= 4 && !(*ppos % 4)) {
+                       u32 val;
+
+                       ret =  mdev_access(mdev, (char *)&val, sizeof(val),
+                                          *ppos, false);
+                       if (ret <= 0)
+                               goto read_err;
+
+                       if (copy_to_user(buf, &val, sizeof(val)))
+                               goto read_err;
+
+                       filled = 4;
+               } else if (count >= 2 && !(*ppos % 2)) {
+                       u16 val;
+
+                       ret = mdev_access(mdev, (char *)&val, sizeof(val),
+                                         *ppos, false);
+                       if (ret <= 0)
+                               goto read_err;
+
+                       if (copy_to_user(buf, &val, sizeof(val)))
+                               goto read_err;
+
+                       filled = 2;
+               } else {
+                       u8 val;
+
+                       ret = mdev_access(mdev, (char *)&val, sizeof(val),
+                                         *ppos, false);
+                       if (ret <= 0)
+                               goto read_err;
+
+                       if (copy_to_user(buf, &val, sizeof(val)))
+                               goto read_err;
+
+                       filled = 1;
+               }
+
+               count -= filled;
+               done += filled;
+               *ppos += filled;
+               buf += filled;
+       }
+
+       return done;
+
+read_err:
+       return -EFAULT;
+}
+
+ssize_t mbochs_write(struct mdev_device *mdev, const char __user *buf,
+                    size_t count, loff_t *ppos)
+{
+       unsigned int done = 0;
+       int ret;
+
+       while (count) {
+               size_t filled;
+
+               if (count >= 4 && !(*ppos % 4)) {
+                       u32 val;
+
+                       if (copy_from_user(&val, buf, sizeof(val)))
+                               goto write_err;
+
+                       ret = mdev_access(mdev, (char *)&val, sizeof(val),
+                                         *ppos, true);
+                       if (ret <= 0)
+                               goto write_err;
+
+                       filled = 4;
+               } else if (count >= 2 && !(*ppos % 2)) {
+                       u16 val;
+
+                       if (copy_from_user(&val, buf, sizeof(val)))
+                               goto write_err;
+
+                       ret = mdev_access(mdev, (char *)&val, sizeof(val),
+                                         *ppos, true);
+                       if (ret <= 0)
+                               goto write_err;
+
+                       filled = 2;
+               } else {
+                       u8 val;
+
+                       if (copy_from_user(&val, buf, sizeof(val)))
+                               goto write_err;
+
+                       ret = mdev_access(mdev, (char *)&val, sizeof(val),
+                                         *ppos, true);
+                       if (ret <= 0)
+                               goto write_err;
+
+                       filled = 1;
+               }
+               count -= filled;
+               done += filled;
+               *ppos += filled;
+               buf += filled;
+       }
+
+       return done;
+write_err:
+       return -EFAULT;
+}
+
+struct page *__mbochs_get_page(struct mdev_state *mdev_state, pgoff_t pgoff)
+{
+       WARN_ON(!mutex_is_locked(&mdev_state->ops_lock));
+
+       if (!mdev_state->pages[pgoff]) {
+               mdev_state->pages[pgoff] =
+                       alloc_pages(GFP_HIGHUSER | __GFP_ZERO, 0);
+               if (!mdev_state->pages[pgoff])
+                       return NULL;
+       }
+
+       get_page(mdev_state->pages[pgoff]);
+       return mdev_state->pages[pgoff];
+}
+
+struct page *mbochs_get_page(struct mdev_state *mdev_state, pgoff_t pgoff)
+{
+       struct page *page;
+
+       if (WARN_ON(pgoff >= mdev_state->pagecount))
+               return NULL;
+
+       mutex_lock(&mdev_state->ops_lock);
+       page = __mbochs_get_page(mdev_state, pgoff);
+       mutex_unlock(&mdev_state->ops_lock);
+
+       return page;
+}
+
+void mbochs_put_pages(struct mdev_state *mdev_state)
+{
+       struct device *dev = mdev_dev(mdev_state->mdev);
+       int i, count = 0;
+
+       WARN_ON(!mutex_is_locked(&mdev_state->ops_lock));
+
+       for (i = 0; i < mdev_state->pagecount; i++) {
+               if (!mdev_state->pages[i])
+                       continue;
+               put_page(mdev_state->pages[i]);
+               mdev_state->pages[i] = NULL;
+               count++;
+       }
+       dev_dbg(dev, "%s: %d pages released\n", __func__, count);
+}
+
+static int mbochs_region_vm_fault(struct vm_fault *vmf)
+{
+       struct vm_area_struct *vma = vmf->vma;
+       struct mdev_state *mdev_state = vma->vm_private_data;
+       pgoff_t page_offset = (vmf->address - vma->vm_start) >> PAGE_SHIFT;
+
+       if (page_offset >= mdev_state->pagecount)
+               return VM_FAULT_SIGBUS;
+
+       vmf->page = mbochs_get_page(mdev_state, page_offset);
+       if (!vmf->page)
+               return VM_FAULT_SIGBUS;
+
+       return 0;
+}
+
+static const struct vm_operations_struct mbochs_region_vm_ops = {
+       .fault = mbochs_region_vm_fault,
+};
+
+int mbochs_mmap(struct mdev_device *mdev, struct vm_area_struct *vma)
+{
+       struct mdev_state *mdev_state = mdev_get_drvdata(mdev);
+
+       if (vma->vm_pgoff != MBOCHS_MEMORY_BAR_OFFSET >> PAGE_SHIFT)
+               return -EINVAL;
+       if (vma->vm_end < vma->vm_start)
+               return -EINVAL;
+       if (vma->vm_end - vma->vm_start > mdev_state->memsize)
+               return -EINVAL;
+       if ((vma->vm_flags & VM_SHARED) == 0)
+               return -EINVAL;
+
+       vma->vm_ops = &mbochs_region_vm_ops;
+       vma->vm_private_data = mdev_state;
+       return 0;
+}
+
+static int mbochs_dmabuf_vm_fault(struct vm_fault *vmf)
+{
+       struct vm_area_struct *vma = vmf->vma;
+       struct mbochs_dmabuf *dmabuf = vma->vm_private_data;
+
+       if (WARN_ON(vmf->pgoff >= dmabuf->pagecount))
+               return VM_FAULT_SIGBUS;
+
+       vmf->page = dmabuf->pages[vmf->pgoff];
+       get_page(vmf->page);
+       return 0;
+}
+
+static const struct vm_operations_struct mbochs_dmabuf_vm_ops = {
+       .fault = mbochs_dmabuf_vm_fault,
+};
+
+static int mbochs_mmap_dmabuf(struct dma_buf *buf, struct vm_area_struct *vma)
+{
+       struct mbochs_dmabuf *dmabuf = buf->priv;
+       struct device *dev = mdev_dev(dmabuf->mdev_state->mdev);
+
+       dev_dbg(dev, "%s: %d\n", __func__, dmabuf->id);
+
+       if ((vma->vm_flags & VM_SHARED) == 0)
+               return -EINVAL;
+
+       vma->vm_ops = &mbochs_dmabuf_vm_ops;
+       vma->vm_private_data = dmabuf;
+       return 0;
+}
+
+static void mbochs_print_dmabuf(struct mbochs_dmabuf *dmabuf,
+                               const char *prefix)
+{
+       struct device *dev = mdev_dev(dmabuf->mdev_state->mdev);
+       u32 fourcc = dmabuf->mode.drm_format;
+
+       dev_dbg(dev, "%s/%d: %c%c%c%c, %dx%d, stride %d, off 0x%llx, size 
0x%llx, pages %ld\n",
+               prefix, dmabuf->id,
+               fourcc ? ((fourcc >>  0) & 0xff) : '-',
+               fourcc ? ((fourcc >>  8) & 0xff) : '-',
+               fourcc ? ((fourcc >> 16) & 0xff) : '-',
+               fourcc ? ((fourcc >> 24) & 0xff) : '-',
+               dmabuf->mode.width, dmabuf->mode.height, dmabuf->mode.stride,
+               dmabuf->mode.offset, dmabuf->mode.size, dmabuf->pagecount);
+}
+
+static struct sg_table *mbochs_map_dmabuf(struct dma_buf_attachment *at,
+                                         enum dma_data_direction direction)
+{
+       struct mbochs_dmabuf *dmabuf = at->dmabuf->priv;
+       struct device *dev = mdev_dev(dmabuf->mdev_state->mdev);
+       struct sg_table *sg;
+
+       dev_dbg(dev, "%s: %d\n", __func__, dmabuf->id);
+
+       sg = kzalloc(sizeof(*sg), GFP_KERNEL);
+       if (!sg)
+               goto err1;
+       if (sg_alloc_table_from_pages(sg, dmabuf->pages, dmabuf->pagecount,
+                                     0, dmabuf->mode.size, GFP_KERNEL) < 0)
+               goto err2;
+       if (!dma_map_sg(at->dev, sg->sgl, sg->nents, direction))
+               goto err3;
+
+       return sg;
+
+err3:
+       sg_free_table(sg);
+err2:
+       kfree(sg);
+err1:
+       return ERR_PTR(-ENOMEM);
+}
+
+static void mbochs_unmap_dmabuf(struct dma_buf_attachment *at,
+                               struct sg_table *sg,
+                               enum dma_data_direction direction)
+{
+       struct mbochs_dmabuf *dmabuf = at->dmabuf->priv;
+       struct device *dev = mdev_dev(dmabuf->mdev_state->mdev);
+
+       dev_dbg(dev, "%s: %d\n", __func__, dmabuf->id);
+
+       sg_free_table(sg);
+       kfree(sg);
+}
+
+static void mbochs_release_dmabuf(struct dma_buf *buf)
+{
+       struct mbochs_dmabuf *dmabuf = buf->priv;
+       struct mdev_state *mdev_state = dmabuf->mdev_state;
+       struct device *dev = mdev_dev(mdev_state->mdev);
+       pgoff_t pg;
+
+       dev_dbg(dev, "%s: %d\n", __func__, dmabuf->id);
+
+       for (pg = 0; pg < dmabuf->pagecount; pg++)
+               put_page(dmabuf->pages[pg]);
+
+       mutex_lock(&mdev_state->ops_lock);
+       dmabuf->buf = NULL;
+       if (dmabuf->unlinked)
+               kfree(dmabuf);
+       mutex_unlock(&mdev_state->ops_lock);
+}
+
+static void *mbochs_kmap_atomic_dmabuf(struct dma_buf *buf, unsigned long 
page_num)
+{
+       struct mbochs_dmabuf *dmabuf = buf->priv;
+       struct page *page = dmabuf->pages[page_num];
+
+       return kmap_atomic(page);
+}
+
+static void *mbochs_kmap_dmabuf(struct dma_buf *buf, unsigned long page_num)
+{
+       struct mbochs_dmabuf *dmabuf = buf->priv;
+       struct page *page = dmabuf->pages[page_num];
+
+       return kmap(page);
+}
+
+static struct dma_buf_ops mbochs_dmabuf_ops = {
+       .map_dma_buf      = mbochs_map_dmabuf,
+       .unmap_dma_buf    = mbochs_unmap_dmabuf,
+       .release          = mbochs_release_dmabuf,
+       .map_atomic       = mbochs_kmap_atomic_dmabuf,
+       .map              = mbochs_kmap_dmabuf,
+       .mmap             = mbochs_mmap_dmabuf,
+};
+
+static struct mbochs_dmabuf *mbochs_dmabuf_alloc(struct mdev_state *mdev_state,
+                                                struct mbochs_mode *mode)
+{
+       struct mbochs_dmabuf *dmabuf;
+       pgoff_t page_offset, pg;
+
+       WARN_ON(!mutex_is_locked(&mdev_state->ops_lock));
+
+       dmabuf = kzalloc(sizeof(struct mbochs_dmabuf), GFP_KERNEL);
+       if (!dmabuf)
+               return NULL;
+
+       dmabuf->mode = *mode;
+       dmabuf->id = mdev_state->next_id++;
+       dmabuf->pagecount = DIV_ROUND_UP(mode->size, PAGE_SIZE);
+       dmabuf->pages = kzalloc(dmabuf->pagecount * sizeof(struct page*),
+                               GFP_KERNEL);
+       if (!dmabuf->pages)
+               goto err_free_dmabuf;
+
+       page_offset = dmabuf->mode.offset >> PAGE_SHIFT;
+       for (pg = 0; pg < dmabuf->pagecount; pg++) {
+               dmabuf->pages[pg] = __mbochs_get_page(mdev_state, page_offset + 
pg);
+               if (!dmabuf->pages[pg])
+                       goto err_free_pages;
+       }
+
+       dmabuf->mdev_state = mdev_state;
+       list_add(&dmabuf->next, &mdev_state->dmabufs);
+
+       mbochs_print_dmabuf(dmabuf, __func__);
+       return dmabuf;
+
+err_free_pages:
+       while (pg > 0)
+               put_page(dmabuf->pages[--pg]);
+       kfree(dmabuf->pages);
+err_free_dmabuf:
+       kfree(dmabuf);
+       return NULL;
+}
+
+static struct mbochs_dmabuf *
+mbochs_dmabuf_find_by_mode(struct mdev_state *mdev_state,
+                          struct mbochs_mode *mode)
+{
+       struct mbochs_dmabuf *dmabuf;
+
+       WARN_ON(!mutex_is_locked(&mdev_state->ops_lock));
+
+       list_for_each_entry(dmabuf, &mdev_state->dmabufs, next)
+               if (mbochs_modes_equal(&dmabuf->mode, mode))
+                       return dmabuf;
+
+       return NULL;
+}
+
+static struct mbochs_dmabuf *
+mbochs_dmabuf_find_by_id(struct mdev_state *mdev_state, u32 id)
+{
+       struct mbochs_dmabuf *dmabuf;
+
+       WARN_ON(!mutex_is_locked(&mdev_state->ops_lock));
+
+       list_for_each_entry(dmabuf, &mdev_state->dmabufs, next)
+               if (dmabuf->id == id)
+                       return dmabuf;
+
+       return NULL;
+}
+
+static int mbochs_dmabuf_export(struct mbochs_dmabuf *dmabuf)
+{
+       struct mdev_state *mdev_state = dmabuf->mdev_state;
+       struct device *dev = mdev_dev(mdev_state->mdev);
+       DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
+       struct dma_buf *buf;
+
+       WARN_ON(!mutex_is_locked(&mdev_state->ops_lock));
+
+       if (!IS_ALIGNED(dmabuf->mode.offset, PAGE_SIZE)) {
+               dev_info_ratelimited(dev, "%s: framebuffer not page-aligned\n",
+                                    __func__);
+               return -EINVAL;
+       }
+
+       exp_info.ops = &mbochs_dmabuf_ops;
+       exp_info.size = dmabuf->mode.size;
+       exp_info.priv = dmabuf;
+
+       buf = dma_buf_export(&exp_info);
+       if (IS_ERR(buf)) {
+               dev_info_ratelimited(dev, "%s: dma_buf_export failed: %ld\n",
+                                    __func__, PTR_ERR(buf));
+               return PTR_ERR(buf);
+       }
+
+       dmabuf->buf = buf;
+       dev_dbg(dev, "%s: %d\n", __func__, dmabuf->id);
+       return 0;
+}
+
+int mbochs_get_region_info(struct mdev_device *mdev,
+                          struct vfio_region_info *region_info,
+                          u16 *cap_type_id, void **cap_type)
+{
+       struct mdev_state *mdev_state;
+
+       mdev_state = mdev_get_drvdata(mdev);
+       if (!mdev_state)
+               return -EINVAL;
+
+       if (region_info->index >= VFIO_PCI_NUM_REGIONS)
+               return -EINVAL;
+
+       switch (region_info->index) {
+       case VFIO_PCI_CONFIG_REGION_INDEX:
+               region_info->offset = 0;
+               region_info->size   = MBOCHS_CONFIG_SPACE_SIZE;
+               region_info->flags  = (VFIO_REGION_INFO_FLAG_READ |
+                                      VFIO_REGION_INFO_FLAG_WRITE);
+               break;
+       case VFIO_PCI_BAR0_REGION_INDEX:
+               region_info->offset = MBOCHS_MEMORY_BAR_OFFSET;
+               region_info->size   = mdev_state->memsize;
+               region_info->flags  = (VFIO_REGION_INFO_FLAG_READ  |
+                                      VFIO_REGION_INFO_FLAG_WRITE |
+                                      VFIO_REGION_INFO_FLAG_MMAP);
+               break;
+       case VFIO_PCI_BAR2_REGION_INDEX:
+               region_info->offset = MBOCHS_MMIO_BAR_OFFSET;
+               region_info->size   = MBOCHS_MMIO_BAR_SIZE;
+               region_info->flags  = (VFIO_REGION_INFO_FLAG_READ  |
+                                      VFIO_REGION_INFO_FLAG_WRITE);
+               break;
+       default:
+               region_info->size   = 0;
+               region_info->offset = 0;
+               region_info->flags  = 0;
+       }
+
+       return 0;
+}
+
+int mbochs_get_irq_info(struct mdev_device *mdev, struct vfio_irq_info 
*irq_info)
+{
+       irq_info->count = 0;
+       return 0;
+}
+
+int mbochs_get_device_info(struct mdev_device *mdev,
+                        struct vfio_device_info *dev_info)
+{
+       dev_info->flags = VFIO_DEVICE_FLAGS_PCI;
+       dev_info->num_regions = VFIO_PCI_NUM_REGIONS;
+       dev_info->num_irqs = VFIO_PCI_NUM_IRQS;
+       return 0;
+}
+
+int mbochs_query_gfx_plane(struct mdev_device *mdev,
+                          struct vfio_device_gfx_plane_info *plane)
+{
+       struct mdev_state *mdev_state = mdev_get_drvdata(mdev);
+       struct device *dev = mdev_dev(mdev);
+       struct mbochs_dmabuf *dmabuf;
+       struct mbochs_mode mode;
+       int ret;
+
+       if (plane->flags & VFIO_GFX_PLANE_TYPE_PROBE) {
+               if (plane->flags == (VFIO_GFX_PLANE_TYPE_PROBE |
+                                    VFIO_GFX_PLANE_TYPE_DMABUF))
+                       return 0;
+               return -EINVAL;
+       }
+
+       if (plane->flags != VFIO_GFX_PLANE_TYPE_DMABUF)
+               return -EINVAL;
+
+       plane->drm_format_mod = 0;
+       plane->x_pos          = 0;
+       plane->y_pos          = 0;
+       plane->x_hot          = 0;
+       plane->y_hot          = 0;
+
+       mutex_lock(&mdev_state->ops_lock);
+
+       ret = -EINVAL;
+       if (plane->drm_plane_type == DRM_PLANE_TYPE_PRIMARY)
+               ret = mbochs_check_framebuffer(mdev_state, &mode);
+       if (ret < 0) {
+               plane->drm_format     = 0;
+               plane->width          = 0;
+               plane->height         = 0;
+               plane->stride         = 0;
+               plane->size           = 0;
+               plane->dmabuf_id      = 0;
+               goto done;
+       }
+
+       dmabuf = mbochs_dmabuf_find_by_mode(mdev_state, &mode);
+       if (!dmabuf)
+               mbochs_dmabuf_alloc(mdev_state, &mode);
+       if (!dmabuf) {
+               mutex_unlock(&mdev_state->ops_lock);
+               return -ENOMEM;
+       }
+
+       plane->drm_format     = dmabuf->mode.drm_format;
+       plane->width          = dmabuf->mode.width;
+       plane->height         = dmabuf->mode.height;
+       plane->stride         = dmabuf->mode.stride;
+       plane->size           = dmabuf->mode.size;
+       plane->dmabuf_id      = dmabuf->id;
+
+done:
+       if (plane->drm_plane_type == DRM_PLANE_TYPE_PRIMARY &&
+           mdev_state->active_id != plane->dmabuf_id) {
+               dev_dbg(dev, "%s: primary: %d => %d\n", __func__,
+                       mdev_state->active_id, plane->dmabuf_id);
+               mdev_state->active_id = plane->dmabuf_id;
+       }
+       mutex_unlock(&mdev_state->ops_lock);
+       return 0;
+}
+
+int mbochs_get_gfx_dmabuf(struct mdev_device *mdev,
+                         u32 id)
+{
+       struct mdev_state *mdev_state = mdev_get_drvdata(mdev);
+       struct mbochs_dmabuf *dmabuf;
+
+       mutex_lock(&mdev_state->ops_lock);
+
+       dmabuf = mbochs_dmabuf_find_by_id(mdev_state, id);
+       if (!dmabuf) {
+               mutex_unlock(&mdev_state->ops_lock);
+               return -ENOENT;
+       }
+
+       if (!dmabuf->buf)
+               mbochs_dmabuf_export(dmabuf);
+
+       mutex_unlock(&mdev_state->ops_lock);
+
+       if (!dmabuf->buf)
+               return -EINVAL;
+
+       return dma_buf_fd(dmabuf->buf, 0);
+}
+
+static long mbochs_ioctl(struct mdev_device *mdev, unsigned int cmd,
+                       unsigned long arg)
+{
+       int ret = 0;
+       unsigned long minsz;
+       struct mdev_state *mdev_state;
+
+       mdev_state = mdev_get_drvdata(mdev);
+
+       switch (cmd) {
+       case VFIO_DEVICE_GET_INFO:
+       {
+               struct vfio_device_info info;
+
+               minsz = offsetofend(struct vfio_device_info, num_irqs);
+
+               if (copy_from_user(&info, (void __user *)arg, minsz))
+                       return -EFAULT;
+
+               if (info.argsz < minsz)
+                       return -EINVAL;
+
+               ret = mbochs_get_device_info(mdev, &info);
+               if (ret)
+                       return ret;
+
+               memcpy(&mdev_state->dev_info, &info, sizeof(info));
+
+               if (copy_to_user((void __user *)arg, &info, minsz))
+                       return -EFAULT;
+
+               return 0;
+       }
+       case VFIO_DEVICE_GET_REGION_INFO:
+       {
+               struct vfio_region_info info;
+               u16 cap_type_id = 0;
+               void *cap_type = NULL;
+
+               minsz = offsetofend(struct vfio_region_info, offset);
+
+               if (copy_from_user(&info, (void __user *)arg, minsz))
+                       return -EFAULT;
+
+               if (info.argsz < minsz)
+                       return -EINVAL;
+
+               ret = mbochs_get_region_info(mdev, &info, &cap_type_id,
+                                          &cap_type);
+               if (ret)
+                       return ret;
+
+               if (copy_to_user((void __user *)arg, &info, minsz))
+                       return -EFAULT;
+
+               return 0;
+       }
+
+       case VFIO_DEVICE_GET_IRQ_INFO:
+       {
+               struct vfio_irq_info info;
+
+               minsz = offsetofend(struct vfio_irq_info, count);
+
+               if (copy_from_user(&info, (void __user *)arg, minsz))
+                       return -EFAULT;
+
+               if ((info.argsz < minsz) ||
+                   (info.index >= mdev_state->dev_info.num_irqs))
+                       return -EINVAL;
+
+               ret = mbochs_get_irq_info(mdev, &info);
+               if (ret)
+                       return ret;
+
+               if (copy_to_user((void __user *)arg, &info, minsz))
+                       return -EFAULT;
+
+               return 0;
+       }
+
+       case VFIO_DEVICE_QUERY_GFX_PLANE:
+       {
+               struct vfio_device_gfx_plane_info plane;
+
+               minsz = offsetofend(struct vfio_device_gfx_plane_info,
+                                   region_index);
+
+               if (copy_from_user(&plane, (void __user *)arg, minsz))
+                       return -EFAULT;
+
+               if (plane.argsz < minsz)
+                       return -EINVAL;
+
+               ret = mbochs_query_gfx_plane(mdev, &plane);
+               if (ret)
+                       return ret;
+
+               if (copy_to_user((void __user *)arg, &plane, minsz))
+                       return -EFAULT;
+
+               return 0;
+       }
+
+       case VFIO_DEVICE_GET_GFX_DMABUF:
+       {
+               u32 dmabuf_id;
+
+               if (get_user(dmabuf_id, (__u32 __user *)arg))
+                       return -EFAULT;
+
+               return mbochs_get_gfx_dmabuf(mdev, dmabuf_id);
+       }
+
+       case VFIO_DEVICE_SET_IRQS:
+               return -EINVAL;
+
+       case VFIO_DEVICE_RESET:
+               return mbochs_reset(mdev);
+       }
+       return -ENOTTY;
+}
+
+int mbochs_open(struct mdev_device *mdev)
+{
+       if (!try_module_get(THIS_MODULE))
+               return -ENODEV;
+
+       return 0;
+}
+
+void mbochs_close(struct mdev_device *mdev)
+{
+       struct mdev_state *mdev_state = mdev_get_drvdata(mdev);
+       struct mbochs_dmabuf *dmabuf, *tmp;
+
+       mutex_lock(&mdev_state->ops_lock);
+
+       list_for_each_entry_safe(dmabuf, tmp, &mdev_state->dmabufs, next) {
+               list_del(&dmabuf->next);
+               if (dmabuf->buf) {
+                       /* free in mbochs_release_dmabuf() */
+                       dmabuf->unlinked = true;
+               } else {
+                       kfree(dmabuf);
+               }
+       }
+       mbochs_put_pages(mdev_state);
+
+       mutex_unlock(&mdev_state->ops_lock);
+       module_put(THIS_MODULE);
+}
+
+static ssize_t
+memory_show(struct device *dev, struct device_attribute *attr,
+           char *buf)
+{
+       struct mdev_device *mdev = mdev_from_dev(dev);
+       struct mdev_state *mdev_state = mdev_get_drvdata(mdev);
+
+       return sprintf(buf, "%d MB\n", mdev_state->type->mbytes);
+}
+static DEVICE_ATTR_RO(memory);
+
+static struct attribute *mdev_dev_attrs[] = {
+       &dev_attr_memory.attr,
+       NULL,
+};
+
+static const struct attribute_group mdev_dev_group = {
+       .name  = "vendor",
+       .attrs = mdev_dev_attrs,
+};
+
+const struct attribute_group *mdev_dev_groups[] = {
+       &mdev_dev_group,
+       NULL,
+};
+
+static ssize_t
+name_show(struct kobject *kobj, struct device *dev, char *buf)
+{
+       return sprintf(buf, "%s\n", kobj->name);
+}
+MDEV_TYPE_ATTR_RO(name);
+
+static ssize_t
+description_show(struct kobject *kobj, struct device *dev, char *buf)
+{
+       const struct mbochs_type *type = mbochs_find_type(kobj);
+
+       return sprintf(buf, "virtual display, %d MB video memory\n",
+                      type ? type->mbytes  : 0);
+}
+MDEV_TYPE_ATTR_RO(description);
+
+static ssize_t
+available_instances_show(struct kobject *kobj, struct device *dev, char *buf)
+{
+       const struct mbochs_type *type = mbochs_find_type(kobj);
+       int count = (max_mbytes - mbochs_used_mbytes) / type->mbytes;
+
+       return sprintf(buf, "%d\n", count);
+}
+MDEV_TYPE_ATTR_RO(available_instances);
+
+static ssize_t device_api_show(struct kobject *kobj, struct device *dev,
+                              char *buf)
+{
+       return sprintf(buf, "%s\n", VFIO_DEVICE_API_PCI_STRING);
+}
+MDEV_TYPE_ATTR_RO(device_api);
+
+static struct attribute *mdev_types_attrs[] = {
+       &mdev_type_attr_name.attr,
+       &mdev_type_attr_description.attr,
+       &mdev_type_attr_device_api.attr,
+       &mdev_type_attr_available_instances.attr,
+       NULL,
+};
+
+static struct attribute_group mdev_type_group1 = {
+       .name  = MBOCHS_TYPE_1,
+       .attrs = mdev_types_attrs,
+};
+
+static struct attribute_group mdev_type_group2 = {
+       .name  = MBOCHS_TYPE_2,
+       .attrs = mdev_types_attrs,
+};
+
+static struct attribute_group mdev_type_group3 = {
+       .name  = MBOCHS_TYPE_3,
+       .attrs = mdev_types_attrs,
+};
+
+static struct attribute_group *mdev_type_groups[] = {
+       &mdev_type_group1,
+       &mdev_type_group2,
+       &mdev_type_group3,
+       NULL,
+};
+
+static const struct mdev_parent_ops mdev_fops = {
+       .owner                  = THIS_MODULE,
+       .mdev_attr_groups       = mdev_dev_groups,
+       .supported_type_groups  = mdev_type_groups,
+       .create                 = mbochs_create,
+       .remove                 = mbochs_remove,
+       .open                   = mbochs_open,
+       .release                = mbochs_close,
+       .read                   = mbochs_read,
+       .write                  = mbochs_write,
+       .ioctl                  = mbochs_ioctl,
+       .mmap                   = mbochs_mmap,
+};
+
+static const struct file_operations vd_fops = {
+       .owner          = THIS_MODULE,
+};
+
+static void mbochs_device_release(struct device *dev)
+{
+       /* nothing */
+}
+
+static int __init mbochs_dev_init(void)
+{
+       int ret = 0;
+
+       ret = alloc_chrdev_region(&mbochs_devt, 0, MINORMASK, MBOCHS_NAME);
+       if (ret < 0) {
+               pr_err("Error: failed to register mbochs_dev, err: %d\n", ret);
+               return ret;
+       }
+       cdev_init(&mbochs_cdev, &vd_fops);
+       cdev_add(&mbochs_cdev, mbochs_devt, MINORMASK);
+       pr_info("%s: major %d\n", __func__, MAJOR(mbochs_devt));
+
+       mbochs_class = class_create(THIS_MODULE, MBOCHS_CLASS_NAME);
+       if (IS_ERR(mbochs_class)) {
+               pr_err("Error: failed to register mbochs_dev class\n");
+               ret = PTR_ERR(mbochs_class);
+               goto failed1;
+       }
+       mbochs_dev.class = mbochs_class;
+       mbochs_dev.release = mbochs_device_release;
+       dev_set_name(&mbochs_dev, "%s", MBOCHS_NAME);
+
+       ret = device_register(&mbochs_dev);
+       if (ret)
+               goto failed2;
+
+       ret = mdev_register_device(&mbochs_dev, &mdev_fops);
+       if (ret)
+               goto failed3;
+
+       return 0;
+
+failed3:
+       device_unregister(&mbochs_dev);
+failed2:
+       class_destroy(mbochs_class);
+failed1:
+       cdev_del(&mbochs_cdev);
+       unregister_chrdev_region(mbochs_devt, MINORMASK);
+       return ret;
+}
+
+static void __exit mbochs_dev_exit(void)
+{
+       mbochs_dev.bus = NULL;
+       mdev_unregister_device(&mbochs_dev);
+
+       device_unregister(&mbochs_dev);
+       cdev_del(&mbochs_cdev);
+       unregister_chrdev_region(mbochs_devt, MINORMASK);
+       class_destroy(mbochs_class);
+       mbochs_class = NULL;
+}
+
+module_init(mbochs_dev_init)
+module_exit(mbochs_dev_exit)
diff --git a/samples/Kconfig b/samples/Kconfig
index 755430c788..5de0674cdd 100644
--- a/samples/Kconfig
+++ b/samples/Kconfig
@@ -128,6 +128,19 @@ config SAMPLE_VFIO_MDEV_MDPY_FB
        help
          Guest fbdev driver for the virtual display sample driver.
 
+config SAMPLE_VFIO_MDEV_MBOCHS
+       tristate "Build VFIO mdpy example mediated device sample code -- 
loadable modules only"
+       depends on VFIO_MDEV_DEVICE && m
+       help
+         Build a virtual display sample driver for use as a VFIO
+         mediated device.  It supports the region display interface
+         (VFIO_GFX_PLANE_TYPE_DMABUF).
+         Emulate enough of qemu stdvga to make bochs-drm.ko happy.
+         That is basically the vram memory bar and the bochs dispi
+         interface vbe registers in the mmio register bar.
+         Specifically it does *not* include any legacy vga stuff.
+         Device looks alot like "qemu -device secondary-vga".
+
 config SAMPLE_STATX
        bool "Build example extended-stat using code"
        depends on BROKEN
diff --git a/samples/vfio-mdev/Makefile b/samples/vfio-mdev/Makefile
index 7a5790aaec..7db889ca13 100644
--- a/samples/vfio-mdev/Makefile
+++ b/samples/vfio-mdev/Makefile
@@ -1,3 +1,4 @@
 obj-$(CONFIG_SAMPLE_VFIO_MDEV_MTTY) += mtty.o
 obj-$(CONFIG_SAMPLE_VFIO_MDEV_MDPY) += mdpy.o
 obj-$(CONFIG_SAMPLE_VFIO_MDEV_MDPY_FB) += mdpy-fb.o
+obj-$(CONFIG_SAMPLE_VFIO_MDEV_MBOCHS) += mbochs.o
-- 
2.9.3

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