[PATCH 3/3] sample: vfio bochs vbe display (host device for bochs-drm)

[Gerd Hoffmann]

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 <kraxel@xxxxxxxxxx>
---
 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 <kraxel@xxxxxxxxxx>
+ *
+ * based on mtty driver which is:
+ *   Copyright (c) 2016, NVIDIA CORPORATION. All rights reserved.
+ *	 Author: Neo Jia <cjia@xxxxxxxxxx>
+ *		 Kirti Wankhede <kwankhede@xxxxxxxxxx>
+ *
+ * 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