[PATCH 1/1] drm/xen-zcopy: Add Xen zero-copy helper DRM driver

[Oleksandr Andrushchenko]

From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>

Introduce Xen zero-copy helper DRM driver, add user-space API of the driver:
1. DRM_IOCTL_XEN_ZCOPY_DUMB_FROM_REFS
This will create a DRM dumb buffer from grant references provided
by the frontend. The intended usage is:
  - Frontend
    - creates a dumb/display buffer and allocates memory
    - grants foreign access to the buffer pages
    - passes granted references to the backend
  - Backend
    - issues DRM_XEN_ZCOPY_DUMB_FROM_REFS ioctl to map
      granted references and create a dumb buffer
    - requests handle to fd conversion via DRM_IOCTL_PRIME_HANDLE_TO_FD
    - requests real HW driver/consumer to import the PRIME buffer with
      DRM_IOCTL_PRIME_FD_TO_HANDLE
    - uses handle returned by the real HW driver
  - at the end:
    o closes real HW driver's handle with DRM_IOCTL_GEM_CLOSE
    o closes zero-copy driver's handle with DRM_IOCTL_GEM_CLOSE
    o closes file descriptor of the exported buffer

2. DRM_IOCTL_XEN_ZCOPY_DUMB_TO_REFS
This will grant references to a dumb/display buffer's memory provided by the
backend. The intended usage is:
  - Frontend
    - requests backend to allocate dumb/display buffer and grant references
      to its pages
  - Backend
    - requests real HW driver to create a dumb with DRM_IOCTL_MODE_CREATE_DUMB
    - requests handle to fd conversion via DRM_IOCTL_PRIME_HANDLE_TO_FD
    - requests zero-copy driver to import the PRIME buffer with
      DRM_IOCTL_PRIME_FD_TO_HANDLE
    - issues DRM_XEN_ZCOPY_DUMB_TO_REFS ioctl to
      grant references to the buffer's memory.
    - passes grant references to the frontend
 - at the end:
    - closes zero-copy driver's handle with DRM_IOCTL_GEM_CLOSE
    - closes real HW driver's handle with DRM_IOCTL_GEM_CLOSE
    - closes file descriptor of the imported buffer

Implement GEM/IOCTL handling depending on driver mode of operation:
- if GEM is created from grant references, then prepare to create
  a dumb from mapped pages
- if GEM grant references are about to be provided for the
  imported PRIME buffer, then prepare for granting references
  and providing those to user-space

Implement handling of display buffers from backend to/from front
interaction point ov view:
- when importing a buffer from the frontend:
  - allocate/free xen ballooned pages via Xen balloon driver
    or by manually allocating a DMA buffer
  - if DMA buffer is used, then increase/decrease its pages
    reservation accordingly
  - map/unmap foreign pages to the ballooned pages
- when exporting a buffer to the frontend:
  - grant references for the pages of the imported PRIME buffer
  - pass the grants back to user-space, so those can be shared
    with the frontend

Add an option to allocate DMA buffers as backing storage while
importing a frontend's buffer into host's memory:
for those use-cases when exported PRIME buffer will be used by
a device expecting CMA buffers only, it is possible to map
frontend's pages onto contiguous buffer, e.g. allocated via
DMA API.

Implement synchronous buffer deletion: for buffers, created from front's
grant references, synchronization between backend and frontend is needed
on buffer deletion as front expects us to unmap these references after
XENDISPL_OP_DBUF_DESTROY response.
For that reason introduce DRM_IOCTL_XEN_ZCOPY_DUMB_WAIT_FREE IOCTL:
this will block until dumb buffer, with the wait handle provided,
be freed.

The rationale behind implementing own wait handle:
  - dumb buffer handle cannot be used as when the PRIME buffer
    gets exported there are at least 2 handles: one is for the
    backend and another one for the importing application,
    so when backend closes its handle and the other application still
    holds the buffer then there is no way for the backend to tell
    which buffer we want to wait for while calling xen_ioctl_wait_free
  - flink cannot be used as well as it is gone when DRM core
    calls .gem_free_object_unlocked

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
---
 Documentation/gpu/drivers.rst               |   1 +
 Documentation/gpu/xen-zcopy.rst             |  32 +
 drivers/gpu/drm/xen/Kconfig                 |  25 +
 drivers/gpu/drm/xen/Makefile                |   5 +
 drivers/gpu/drm/xen/xen_drm_zcopy.c         | 880 ++++++++++++++++++++++++++++
 drivers/gpu/drm/xen/xen_drm_zcopy_balloon.c | 154 +++++
 drivers/gpu/drm/xen/xen_drm_zcopy_balloon.h |  38 ++
 include/uapi/drm/xen_zcopy_drm.h            | 129 ++++
 8 files changed, 1264 insertions(+)
 create mode 100644 Documentation/gpu/xen-zcopy.rst
 create mode 100644 drivers/gpu/drm/xen/xen_drm_zcopy.c
 create mode 100644 drivers/gpu/drm/xen/xen_drm_zcopy_balloon.c
 create mode 100644 drivers/gpu/drm/xen/xen_drm_zcopy_balloon.h
 create mode 100644 include/uapi/drm/xen_zcopy_drm.h

diff --git a/Documentation/gpu/drivers.rst b/Documentation/gpu/drivers.rst
index d3ab6abae838..900ff1c3d3f1 100644
--- a/Documentation/gpu/drivers.rst
+++ b/Documentation/gpu/drivers.rst
@@ -13,6 +13,7 @@ GPU Driver Documentation
    vc4
    bridge/dw-hdmi
    xen-front
+   xen-zcopy
 
 .. only::  subproject and html
 
diff --git a/Documentation/gpu/xen-zcopy.rst b/Documentation/gpu/xen-zcopy.rst
new file mode 100644
index 000000000000..28d3942af2b8
--- /dev/null
+++ b/Documentation/gpu/xen-zcopy.rst
@@ -0,0 +1,32 @@
+===============================
+Xen zero-copy helper DRM driver
+===============================
+
+This helper driver allows implementing zero-copying use-cases
+when using Xen para-virtualized frontend display driver:
+
+ - a dumb buffer created on backend's side can be shared
+   with the Xen PV frontend driver, so it directly writes
+   into backend's domain memory (into the buffer exported from
+   DRM/KMS driver of a physical display device)
+ - a dumb buffer allocated by the frontend can be imported
+   into physical device DRM/KMS driver, thus allowing to
+   achieve no copying as well
+
+DRM_XEN_ZCOPY_DUMB_FROM_REFS IOCTL
+==================================
+
+.. kernel-doc:: include/uapi/drm/xen_zcopy_drm.h
+   :doc: DRM_XEN_ZCOPY_DUMB_FROM_REFS
+
+DRM_XEN_ZCOPY_DUMB_TO_REFS IOCTL
+================================
+
+.. kernel-doc:: include/uapi/drm/xen_zcopy_drm.h
+   :doc: DRM_XEN_ZCOPY_DUMB_TO_REFS
+
+DRM_XEN_ZCOPY_DUMB_WAIT_FREE IOCTL
+==================================
+
+.. kernel-doc:: include/uapi/drm/xen_zcopy_drm.h
+   :doc: DRM_XEN_ZCOPY_DUMB_WAIT_FREE
diff --git a/drivers/gpu/drm/xen/Kconfig b/drivers/gpu/drm/xen/Kconfig
index 4f4abc91f3b6..31eedb410829 100644
--- a/drivers/gpu/drm/xen/Kconfig
+++ b/drivers/gpu/drm/xen/Kconfig
@@ -5,6 +5,10 @@ config DRM_XEN
 	  Choose this option if you want to enable DRM support
 	  for Xen.
 
+choice
+	prompt "Xen DRM drivers selection"
+	depends on DRM_XEN
+
 config DRM_XEN_FRONTEND
 	tristate "Para-virtualized frontend driver for Xen guest OS"
 	depends on DRM_XEN
@@ -28,3 +32,24 @@ config DRM_XEN_FRONTEND_CMA
 	  contiguous buffers.
 	  Note: in this mode driver cannot use buffers allocated
 	  by the backend.
+
+config DRM_XEN_ZCOPY
+	tristate "Zero copy helper DRM driver for Xen"
+	depends on DRM_XEN
+	depends on DRM
+	select DRM_KMS_HELPER
+	help
+	  Choose this option if you want to enable a zero copy
+	  helper DRM driver for Xen. This is implemented via mapping
+	  of foreign display buffer pages into current domain and
+	  exporting a dumb via PRIME interface. This allows
+	  driver domains to use buffers of unpriveledged guests without
+	  additional memory copying.
+
+config DRM_XEN_ZCOPY_CMA
+	bool "Use CMA to allocate buffers"
+	depends on DRM_XEN_ZCOPY
+	help
+	  Use CMA to allocate display buffers.
+
+endchoice
diff --git a/drivers/gpu/drm/xen/Makefile b/drivers/gpu/drm/xen/Makefile
index 352730dc6c13..832daea761a9 100644
--- a/drivers/gpu/drm/xen/Makefile
+++ b/drivers/gpu/drm/xen/Makefile
@@ -14,3 +14,8 @@ else
 endif
 
 obj-$(CONFIG_DRM_XEN_FRONTEND) += drm_xen_front.o
+
+drm_xen_zcopy-objs := xen_drm_zcopy.o \
+		      xen_drm_zcopy_balloon.o
+
+obj-$(CONFIG_DRM_XEN_ZCOPY) += drm_xen_zcopy.o
diff --git a/drivers/gpu/drm/xen/xen_drm_zcopy.c b/drivers/gpu/drm/xen/xen_drm_zcopy.c
new file mode 100644
index 000000000000..c2fa4fcf1bf6
--- /dev/null
+++ b/drivers/gpu/drm/xen/xen_drm_zcopy.c
@@ -0,0 +1,880 @@
+// SPDX-License-Identifier: GPL-2.0 OR MIT
+
+/*
+ *  Xen zero-copy helper DRM device
+ *
+ * Copyright (C) 2016-2018 EPAM Systems Inc.
+ *
+ * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
+ */
+
+#include <drm/drmP.h>
+#include <drm/drm_gem.h>
+
+#include <linux/dma-buf.h>
+#include <linux/of_device.h>
+#include <linux/platform_device.h>
+
+#include <xen/grant_table.h>
+#include <asm/xen/page.h>
+
+#include <drm/xen_zcopy_drm.h>
+
+#include "xen_drm_zcopy_balloon.h"
+
+struct xen_gem_object {
+	struct drm_gem_object base;
+	uint32_t dumb_handle;
+
+	int otherend_id;
+
+	uint32_t num_pages;
+	grant_ref_t *grefs;
+	/* these are the pages from Xen balloon for allocated Xen GEM object */
+	struct page **pages;
+
+	struct xen_drm_zcopy_balloon balloon;
+
+	/* this will be set if we have imported a PRIME buffer */
+	struct sg_table *sgt;
+	/* map grant handles */
+	grant_handle_t *map_handles;
+	/*
+	 * these are used for synchronous object deletion, e.g.
+	 * when user-space wants to know that the grefs are unmapped
+	 */
+	struct kref refcount;
+	int wait_handle;
+};
+
+struct xen_wait_obj {
+	struct list_head list;
+	struct xen_gem_object *xen_obj;
+	struct completion completion;
+};
+
+struct xen_drv_info {
+	struct drm_device *drm_dev;
+
+	/*
+	 * For buffers, created from front's grant references, synchronization
+	 * between backend and frontend is needed on buffer deletion as front
+	 * expects us to unmap these references after XENDISPL_OP_DBUF_DESTROY
+	 * response. This means that when calling DRM_XEN_ZCOPY_DUMB_WAIT_FREE
+	 * ioctl user-space has to provide some unique handle, so we can tell
+	 * the buffer. For that reason we use IDR to allocate a unique value.
+	 * The rationale behind implementing wait handle as IDR:
+	 * - dumb buffer handle cannot be used as when the PRIME buffer
+	 *   gets exported there are at least 2 handles: one is for the
+	 *   backend and another one for the importing application,
+	 *   so when backend closes its handle and the other application still
+	 *   holds the buffer and then there is no way for the backend to tell
+	 *   which buffer we want to wait for while calling xen_ioctl_wait_free
+	 * - flink cannot be used as well as it is gone when DRM core
+	 *   calls .gem_free_object_unlocked
+	 * - sync_file can be used, but it seems to be an overhead to use it
+	 *   only to get a unique "handle"
+	 */
+	struct list_head wait_obj_list;
+	struct idr idr;
+	spinlock_t idr_lock;
+	spinlock_t wait_list_lock;
+};
+
+static inline struct xen_gem_object *to_xen_gem_obj(
+		struct drm_gem_object *gem_obj)
+{
+	return container_of(gem_obj, struct xen_gem_object, base);
+}
+
+static struct xen_wait_obj *wait_obj_new(struct xen_drv_info *drv_info,
+		struct xen_gem_object *xen_obj)
+{
+	struct xen_wait_obj *wait_obj;
+
+	wait_obj = kzalloc(sizeof(*wait_obj), GFP_KERNEL);
+	if (!wait_obj)
+		return ERR_PTR(-ENOMEM);
+
+	init_completion(&wait_obj->completion);
+	wait_obj->xen_obj = xen_obj;
+
+	spin_lock(&drv_info->wait_list_lock);
+	list_add(&wait_obj->list, &drv_info->wait_obj_list);
+	spin_unlock(&drv_info->wait_list_lock);
+
+	return wait_obj;
+}
+
+static void wait_obj_free(struct xen_drv_info *drv_info,
+		struct xen_wait_obj *wait_obj)
+{
+	struct xen_wait_obj *cur_wait_obj, *q;
+
+	spin_lock(&drv_info->wait_list_lock);
+	list_for_each_entry_safe(cur_wait_obj, q,
+			&drv_info->wait_obj_list, list)
+		if (cur_wait_obj == wait_obj) {
+			list_del(&wait_obj->list);
+			kfree(wait_obj);
+			break;
+		}
+	spin_unlock(&drv_info->wait_list_lock);
+}
+
+static void wait_obj_check_pending(struct xen_drv_info *drv_info)
+{
+	/*
+	 * It is intended to be called from .last_close when
+	 * no pending wait objects should be on the list.
+	 * make sure we don't miss a bug if this is not the case.
+	 */
+	WARN(!list_empty(&drv_info->wait_obj_list),
+			"Removing with pending wait objects!\n");
+}
+
+static int wait_obj_wait(struct xen_wait_obj *wait_obj,
+		uint32_t wait_to_ms)
+{
+	if (wait_for_completion_timeout(&wait_obj->completion,
+			msecs_to_jiffies(wait_to_ms)) <= 0)
+		return -ETIMEDOUT;
+
+	return 0;
+}
+
+static void wait_obj_signal(struct xen_drv_info *drv_info,
+		struct xen_gem_object *xen_obj)
+{
+	struct xen_wait_obj *wait_obj, *q;
+
+	spin_lock(&drv_info->wait_list_lock);
+	list_for_each_entry_safe(wait_obj, q, &drv_info->wait_obj_list, list)
+		if (wait_obj->xen_obj == xen_obj) {
+			DRM_DEBUG("Found xen_obj in the wait list, wake\n");
+			complete_all(&wait_obj->completion);
+		}
+	spin_unlock(&drv_info->wait_list_lock);
+}
+
+static int wait_obj_handle_new(struct xen_drv_info *drv_info,
+		struct xen_gem_object *xen_obj)
+{
+	int ret;
+
+	idr_preload(GFP_KERNEL);
+	spin_lock(&drv_info->idr_lock);
+	ret = idr_alloc(&drv_info->idr, xen_obj, 1, 0, GFP_NOWAIT);
+	spin_unlock(&drv_info->idr_lock);
+	idr_preload_end();
+	return ret;
+}
+
+static void wait_obj_handle_free(struct xen_drv_info *drv_info,
+		struct xen_gem_object *xen_obj)
+{
+	spin_lock(&drv_info->idr_lock);
+	idr_remove(&drv_info->idr, xen_obj->wait_handle);
+	spin_unlock(&drv_info->idr_lock);
+}
+
+static struct xen_gem_object *get_obj_by_wait_handle(
+		struct xen_drv_info *drv_info, int wait_handle)
+{
+	struct xen_gem_object *xen_obj;
+
+	spin_lock(&drv_info->idr_lock);
+	/* check if xen_obj still exists */
+	xen_obj = idr_find(&drv_info->idr, wait_handle);
+	if (xen_obj)
+		kref_get(&xen_obj->refcount);
+	spin_unlock(&drv_info->idr_lock);
+	return xen_obj;
+}
+
+#define xen_page_to_vaddr(page) \
+	((phys_addr_t)pfn_to_kaddr(page_to_xen_pfn(page)))
+
+static int from_refs_unmap(struct device *dev,
+		struct xen_gem_object *xen_obj)
+{
+	struct gnttab_unmap_grant_ref *unmap_ops;
+	int i, ret;
+
+	if (!xen_obj->pages || !xen_obj->map_handles)
+		return 0;
+
+	unmap_ops = kcalloc(xen_obj->num_pages, sizeof(*unmap_ops), GFP_KERNEL);
+	if (!unmap_ops)
+		return -ENOMEM;
+
+	for (i = 0; i < xen_obj->num_pages; i++) {
+		phys_addr_t addr;
+
+		/*
+		 * When unmapping the grant entry for access by host CPUs:
+		 * if <host_addr> or <dev_bus_addr> is zero, that
+		 * field is ignored. If non-zero, they must refer to
+		 * a device/host mapping that is tracked by <handle>
+		 */
+		addr = xen_page_to_vaddr(xen_obj->pages[i]);
+		gnttab_set_unmap_op(&unmap_ops[i], addr,
+#if defined(CONFIG_X86)
+			GNTMAP_host_map | GNTMAP_device_map,
+#else
+			GNTMAP_host_map,
+#endif
+			xen_obj->map_handles[i]);
+		unmap_ops[i].dev_bus_addr = __pfn_to_phys(__pfn_to_mfn(
+				page_to_pfn(xen_obj->pages[i])));
+	}
+
+	ret = gnttab_unmap_refs(unmap_ops, NULL, xen_obj->pages,
+			xen_obj->num_pages);
+	/*
+	 * Even if we didn't unmap properly - continue to rescue whatever
+	 * resources we can.
+	 */
+	if (ret)
+		DRM_ERROR("Failed to unmap grant references, ret %d", ret);
+
+	for (i = 0; i < xen_obj->num_pages; i++) {
+		if (unlikely(unmap_ops[i].status != GNTST_okay))
+			DRM_ERROR("Failed to unmap page %d with ref %d: %d\n",
+					i, xen_obj->grefs[i],
+					unmap_ops[i].status);
+	}
+
+	xen_drm_zcopy_ballooned_pages_free(dev, &xen_obj->balloon,
+			xen_obj->num_pages, xen_obj->pages);
+
+	kfree(xen_obj->pages);
+	xen_obj->pages = NULL;
+	kfree(xen_obj->map_handles);
+	xen_obj->map_handles = NULL;
+	kfree(unmap_ops);
+	kfree(xen_obj->grefs);
+	xen_obj->grefs = NULL;
+	return ret;
+}
+
+static int from_refs_map(struct device *dev, struct xen_gem_object *xen_obj)
+{
+	struct gnttab_map_grant_ref *map_ops = NULL;
+	int ret, i;
+
+	if (xen_obj->pages) {
+		DRM_ERROR("Mapping already mapped pages?\n");
+		return -EINVAL;
+	}
+
+	xen_obj->pages = kcalloc(xen_obj->num_pages, sizeof(*xen_obj->pages),
+			GFP_KERNEL);
+	if (!xen_obj->pages) {
+		ret = -ENOMEM;
+		goto fail;
+	}
+
+	xen_obj->map_handles = kcalloc(xen_obj->num_pages,
+			sizeof(*xen_obj->map_handles), GFP_KERNEL);
+	if (!xen_obj->map_handles) {
+		ret = -ENOMEM;
+		goto fail;
+	}
+
+	map_ops = kcalloc(xen_obj->num_pages, sizeof(*map_ops), GFP_KERNEL);
+	if (!map_ops) {
+		ret = -ENOMEM;
+		goto fail;
+	}
+
+	ret = xen_drm_zcopy_ballooned_pages_alloc(dev, &xen_obj->balloon,
+			xen_obj->num_pages, xen_obj->pages);
+	if (ret < 0) {
+		DRM_ERROR("Cannot allocate %d ballooned pages: %d\n",
+				xen_obj->num_pages, ret);
+		goto fail;
+	}
+
+	for (i = 0; i < xen_obj->num_pages; i++) {
+		phys_addr_t addr;
+
+		addr = xen_page_to_vaddr(xen_obj->pages[i]);
+		gnttab_set_map_op(&map_ops[i], addr,
+#if defined(CONFIG_X86)
+			GNTMAP_host_map | GNTMAP_device_map,
+#else
+			GNTMAP_host_map,
+#endif
+			xen_obj->grefs[i], xen_obj->otherend_id);
+	}
+	ret = gnttab_map_refs(map_ops, NULL, xen_obj->pages,
+			xen_obj->num_pages);
+
+	/* save handles even if error, so we can unmap */
+	for (i = 0; i < xen_obj->num_pages; i++) {
+		xen_obj->map_handles[i] = map_ops[i].handle;
+		if (unlikely(map_ops[i].status != GNTST_okay))
+			DRM_ERROR("Failed to map page %d with ref %d: %d\n",
+				i, xen_obj->grefs[i], map_ops[i].status);
+	}
+
+	if (ret) {
+		DRM_ERROR("Failed to map grant references, ret %d", ret);
+		from_refs_unmap(dev, xen_obj);
+		goto fail;
+	}
+
+	kfree(map_ops);
+	return 0;
+
+fail:
+	kfree(xen_obj->pages);
+	xen_obj->pages = NULL;
+	kfree(xen_obj->map_handles);
+	xen_obj->map_handles = NULL;
+	kfree(map_ops);
+	return ret;
+
+}
+
+static void to_refs_end_foreign_access(struct xen_gem_object *xen_obj)
+{
+	int i;
+
+	if (xen_obj->grefs)
+		for (i = 0; i < xen_obj->num_pages; i++)
+			if (xen_obj->grefs[i] != GRANT_INVALID_REF)
+				gnttab_end_foreign_access(xen_obj->grefs[i],
+						0, 0UL);
+
+	kfree(xen_obj->grefs);
+	xen_obj->grefs = NULL;
+	xen_obj->sgt = NULL;
+}
+
+static int to_refs_grant_foreign_access(struct xen_gem_object *xen_obj)
+{
+	grant_ref_t priv_gref_head;
+	int ret, j, cur_ref, num_pages;
+	struct sg_page_iter sg_iter;
+
+	ret = gnttab_alloc_grant_references(xen_obj->num_pages,
+			&priv_gref_head);
+	if (ret < 0) {
+		DRM_ERROR("Cannot allocate grant references\n");
+		return ret;
+	}
+
+	j = 0;
+	num_pages = xen_obj->num_pages;
+	for_each_sg_page(xen_obj->sgt->sgl, &sg_iter, xen_obj->sgt->nents, 0) {
+		struct page *page;
+
+		page = sg_page_iter_page(&sg_iter);
+		cur_ref = gnttab_claim_grant_reference(&priv_gref_head);
+		if (cur_ref < 0)
+			return cur_ref;
+
+		gnttab_grant_foreign_access_ref(cur_ref,
+				xen_obj->otherend_id, xen_page_to_gfn(page), 0);
+		xen_obj->grefs[j++] = cur_ref;
+		num_pages--;
+	}
+
+	WARN_ON(num_pages != 0);
+
+	gnttab_free_grant_references(priv_gref_head);
+	return 0;
+}
+
+static int gem_create_with_handle(struct xen_gem_object *xen_obj,
+		struct drm_file *filp, struct drm_device *dev, int size)
+{
+	struct drm_gem_object *gem_obj;
+	int ret;
+
+	drm_gem_private_object_init(dev, &xen_obj->base, size);
+	gem_obj = &xen_obj->base;
+	ret = drm_gem_handle_create(filp, gem_obj, &xen_obj->dumb_handle);
+	/* drop reference from allocate - handle holds it now. */
+	drm_gem_object_put_unlocked(gem_obj);
+	return ret;
+}
+
+static int gem_create_obj(struct xen_gem_object *xen_obj,
+		struct drm_device *dev, struct drm_file *filp, int size)
+{
+	struct drm_gem_object *gem_obj;
+	int ret;
+
+	ret = gem_create_with_handle(xen_obj, filp, dev, size);
+	if (ret < 0)
+		goto fail;
+
+	gem_obj = drm_gem_object_lookup(filp, xen_obj->dumb_handle);
+	if (!gem_obj) {
+		DRM_ERROR("Lookup for handle %d failed\n",
+				xen_obj->dumb_handle);
+		ret = -EINVAL;
+		goto fail_destroy;
+	}
+
+	drm_gem_object_put_unlocked(gem_obj);
+	return 0;
+
+fail_destroy:
+	drm_gem_dumb_destroy(filp, dev, xen_obj->dumb_handle);
+fail:
+	DRM_ERROR("Failed to create dumb buffer: %d\n", ret);
+	xen_obj->dumb_handle = 0;
+	return ret;
+}
+
+static int gem_init_obj(struct xen_gem_object *xen_obj,
+		struct drm_device *dev, int size)
+{
+	struct drm_gem_object *gem_obj = &xen_obj->base;
+	int ret;
+
+	ret = drm_gem_object_init(dev, gem_obj, size);
+	if (ret < 0)
+		return ret;
+
+	ret = drm_gem_create_mmap_offset(gem_obj);
+	if (ret < 0) {
+		drm_gem_object_release(gem_obj);
+		return ret;
+	}
+
+	return 0;
+}
+
+static void obj_release(struct kref *kref)
+{
+	struct xen_gem_object *xen_obj =
+			container_of(kref, struct xen_gem_object, refcount);
+	struct xen_drv_info *drv_info = xen_obj->base.dev->dev_private;
+
+	wait_obj_signal(drv_info, xen_obj);
+	kfree(xen_obj);
+}
+
+static void gem_free_object_unlocked(struct drm_gem_object *gem_obj)
+{
+	struct xen_gem_object *xen_obj = to_xen_gem_obj(gem_obj);
+	struct xen_drv_info *drv_info = gem_obj->dev->dev_private;
+
+	DRM_DEBUG("Freeing dumb with handle %d\n", xen_obj->dumb_handle);
+	if (xen_obj->grefs) {
+		if (xen_obj->sgt) {
+			drm_prime_gem_destroy(&xen_obj->base, xen_obj->sgt);
+			to_refs_end_foreign_access(xen_obj);
+		} else
+			from_refs_unmap(gem_obj->dev->dev, xen_obj);
+	}
+
+	drm_gem_object_release(gem_obj);
+
+	wait_obj_handle_free(drv_info, xen_obj);
+	kref_put(&xen_obj->refcount, obj_release);
+}
+
+static struct sg_table *gem_prime_get_sg_table(
+		struct drm_gem_object *gem_obj)
+{
+	struct xen_gem_object *xen_obj = to_xen_gem_obj(gem_obj);
+	struct sg_table *sgt = NULL;
+
+	if (unlikely(!xen_obj->pages))
+		return NULL;
+
+	sgt = drm_prime_pages_to_sg(xen_obj->pages, xen_obj->num_pages);
+
+	if (unlikely(!sgt))
+		DRM_ERROR("Failed to export sgt\n");
+	else
+		DRM_DEBUG("Exporting %scontiguous buffer nents %d\n",
+				sgt->nents == 1 ? "" : "non-", sgt->nents);
+	return sgt;
+}
+
+struct drm_gem_object *gem_prime_import_sg_table(struct drm_device *dev,
+		struct dma_buf_attachment *attach, struct sg_table *sgt)
+{
+	struct xen_gem_object *xen_obj;
+	int ret;
+
+	xen_obj = kzalloc(sizeof(*xen_obj), GFP_KERNEL);
+	if (!xen_obj)
+		return ERR_PTR(-ENOMEM);
+
+	ret = gem_init_obj(xen_obj, dev, attach->dmabuf->size);
+	if (ret < 0)
+		goto fail;
+
+	kref_init(&xen_obj->refcount);
+	xen_obj->sgt = sgt;
+	xen_obj->num_pages = DIV_ROUND_UP(attach->dmabuf->size, PAGE_SIZE);
+
+	DRM_DEBUG("Imported buffer of size %zu with nents %u\n",
+			attach->dmabuf->size, sgt->nents);
+	return &xen_obj->base;
+
+fail:
+	kfree(xen_obj);
+	return ERR_PTR(ret);
+}
+
+static int do_ioctl_from_refs(struct drm_device *dev,
+		struct drm_xen_zcopy_dumb_from_refs *req,
+		struct drm_file *filp)
+{
+	struct xen_drv_info *drv_info = dev->dev_private;
+	struct xen_gem_object *xen_obj;
+	int ret;
+
+	xen_obj = kzalloc(sizeof(*xen_obj), GFP_KERNEL);
+	if (!xen_obj)
+		return -ENOMEM;
+
+	kref_init(&xen_obj->refcount);
+	xen_obj->num_pages = req->num_grefs;
+	xen_obj->otherend_id = req->otherend_id;
+	xen_obj->grefs = kcalloc(xen_obj->num_pages,
+			sizeof(grant_ref_t), GFP_KERNEL);
+	if (!xen_obj->grefs) {
+		ret = -ENOMEM;
+		goto fail;
+	}
+
+	if (copy_from_user(xen_obj->grefs, req->grefs,
+			xen_obj->num_pages * sizeof(grant_ref_t))) {
+		ret = -EINVAL;
+		goto fail;
+	}
+
+	ret = from_refs_map(dev->dev, xen_obj);
+	if (ret < 0)
+		goto fail;
+
+	ret = gem_create_obj(xen_obj, dev, filp,
+			round_up(req->dumb.size, PAGE_SIZE));
+	if (ret < 0)
+		goto fail;
+
+	req->dumb.handle = xen_obj->dumb_handle;
+
+	/*
+	 * Get user-visible handle for this GEM object.
+	 * the wait object is not allocated at the moment,
+	 * but if need be it will be allocated at the time of
+	 * DRM_XEN_ZCOPY_DUMB_WAIT_FREE IOCTL
+	 */
+	ret = wait_obj_handle_new(drv_info, xen_obj);
+	if (ret < 0)
+		goto fail;
+
+	req->wait_handle = ret;
+	xen_obj->wait_handle = ret;
+	return 0;
+
+fail:
+	kfree(xen_obj->grefs);
+	xen_obj->grefs = NULL;
+	kfree(xen_obj);
+	return ret;
+}
+
+static int ioctl_from_refs(struct drm_device *dev,
+		void *data, struct drm_file *filp)
+{
+	struct drm_xen_zcopy_dumb_from_refs *req =
+			(struct drm_xen_zcopy_dumb_from_refs *)data;
+	struct drm_mode_create_dumb *args = &req->dumb;
+	uint32_t cpp, stride, size;
+
+	if (!req->num_grefs || !req->grefs)
+		return -EINVAL;
+
+	if (!args->width || !args->height || !args->bpp)
+		return -EINVAL;
+
+	cpp = DIV_ROUND_UP(args->bpp, 8);
+	if (!cpp || cpp > 0xffffffffU / args->width)
+		return -EINVAL;
+
+	stride = cpp * args->width;
+	if (args->height > 0xffffffffU / stride)
+		return -EINVAL;
+
+	size = args->height * stride;
+	if (PAGE_ALIGN(size) == 0)
+		return -EINVAL;
+
+	args->pitch = DIV_ROUND_UP(args->width * args->bpp, 8);
+	args->size = args->pitch * args->height;
+	args->handle = 0;
+	if (req->num_grefs < DIV_ROUND_UP(args->size, PAGE_SIZE)) {
+		DRM_ERROR("Provided %d pages, need %d\n", req->num_grefs,
+				(int)DIV_ROUND_UP(args->size, PAGE_SIZE));
+		return -EINVAL;
+	}
+
+	return do_ioctl_from_refs(dev, req, filp);
+}
+
+static int ioctl_to_refs(struct drm_device *dev,
+		void *data, struct drm_file *filp)
+{
+	struct xen_gem_object *xen_obj;
+	struct drm_gem_object *gem_obj;
+	struct drm_xen_zcopy_dumb_to_refs *req =
+			(struct drm_xen_zcopy_dumb_to_refs *)data;
+	int ret;
+
+	if (!req->num_grefs || !req->grefs)
+		return -EINVAL;
+
+	gem_obj = drm_gem_object_lookup(filp, req->handle);
+	if (!gem_obj) {
+		DRM_ERROR("Lookup for handle %d failed\n", req->handle);
+		return -EINVAL;
+	}
+
+	drm_gem_object_put_unlocked(gem_obj);
+	xen_obj = to_xen_gem_obj(gem_obj);
+
+	if (xen_obj->num_pages != req->num_grefs) {
+		DRM_ERROR("Provided %d pages, need %d\n", req->num_grefs,
+				xen_obj->num_pages);
+		return -EINVAL;
+	}
+
+	xen_obj->otherend_id = req->otherend_id;
+	xen_obj->grefs = kcalloc(xen_obj->num_pages,
+			sizeof(grant_ref_t), GFP_KERNEL);
+	if (!xen_obj->grefs) {
+		ret = -ENOMEM;
+		goto fail;
+	}
+
+	ret = to_refs_grant_foreign_access(xen_obj);
+	if (ret < 0)
+		goto fail;
+
+	if (copy_to_user(req->grefs, xen_obj->grefs,
+			xen_obj->num_pages * sizeof(grant_ref_t))) {
+		ret = -EINVAL;
+		goto fail;
+	}
+
+	return 0;
+
+fail:
+	to_refs_end_foreign_access(xen_obj);
+	return ret;
+}
+
+static int ioctl_wait_free(struct drm_device *dev,
+		void *data, struct drm_file *file_priv)
+{
+	struct drm_xen_zcopy_dumb_wait_free *req =
+			(struct drm_xen_zcopy_dumb_wait_free *)data;
+	struct xen_drv_info *drv_info = dev->dev_private;
+	struct xen_gem_object *xen_obj;
+	struct xen_wait_obj *wait_obj;
+	int wait_handle, ret;
+
+	wait_handle = req->wait_handle;
+	/*
+	 * try to find the wait handle: if not found means that
+	 * either the handle has already been freed or wrong
+	 */
+	xen_obj = get_obj_by_wait_handle(drv_info, wait_handle);
+	if (!xen_obj)
+		return -ENOENT;
+
+	/*
+	 * xen_obj still exists and is reference count locked by us now, so
+	 * prepare to wait: allocate wait object and add it to the wait list,
+	 * so we can find it on release
+	 */
+	wait_obj = wait_obj_new(drv_info, xen_obj);
+	/* put our reference and wait for xen_obj release to fire */
+	kref_put(&xen_obj->refcount, obj_release);
+	ret = PTR_ERR_OR_ZERO(wait_obj);
+	if (ret < 0) {
+		DRM_ERROR("Failed to setup wait object, ret %d\n", ret);
+		return ret;
+	}
+
+	ret = wait_obj_wait(wait_obj, req->wait_to_ms);
+	wait_obj_free(drv_info, wait_obj);
+	return ret;
+}
+
+static void lastclose(struct drm_device *dev)
+{
+	struct xen_drv_info *drv_info = dev->dev_private;
+
+	wait_obj_check_pending(drv_info);
+}
+
+static const struct drm_ioctl_desc xen_drm_ioctls[] = {
+	DRM_IOCTL_DEF_DRV(XEN_ZCOPY_DUMB_FROM_REFS,
+		ioctl_from_refs,
+		DRM_AUTH | DRM_CONTROL_ALLOW | DRM_UNLOCKED),
+	DRM_IOCTL_DEF_DRV(XEN_ZCOPY_DUMB_TO_REFS,
+		ioctl_to_refs,
+		DRM_AUTH | DRM_CONTROL_ALLOW | DRM_UNLOCKED),
+	DRM_IOCTL_DEF_DRV(XEN_ZCOPY_DUMB_WAIT_FREE,
+		ioctl_wait_free,
+		DRM_AUTH | DRM_CONTROL_ALLOW | DRM_UNLOCKED),
+};
+
+static const struct file_operations xen_drm_fops = {
+	.owner          = THIS_MODULE,
+	.open           = drm_open,
+	.release        = drm_release,
+	.unlocked_ioctl = drm_ioctl,
+};
+
+static struct drm_driver xen_drm_driver = {
+	.driver_features           = DRIVER_GEM | DRIVER_PRIME,
+	.lastclose                 = lastclose,
+	.prime_handle_to_fd        = drm_gem_prime_handle_to_fd,
+	.gem_prime_export          = drm_gem_prime_export,
+	.gem_prime_get_sg_table    = gem_prime_get_sg_table,
+	.prime_fd_to_handle        = drm_gem_prime_fd_to_handle,
+	.gem_prime_import          = drm_gem_prime_import,
+	.gem_prime_import_sg_table = gem_prime_import_sg_table,
+	.gem_free_object_unlocked  = gem_free_object_unlocked,
+	.fops                      = &xen_drm_fops,
+	.ioctls                    = xen_drm_ioctls,
+	.num_ioctls                = ARRAY_SIZE(xen_drm_ioctls),
+	.name                      = XENDRM_ZCOPY_DRIVER_NAME,
+	.desc                      = "Xen PV DRM zero copy",
+	.date                      = "20180221",
+	.major                     = 1,
+	.minor                     = 0,
+};
+
+static int xen_drm_drv_remove(struct platform_device *pdev)
+{
+	struct xen_drv_info *drv_info = platform_get_drvdata(pdev);
+
+	if (drv_info && drv_info->drm_dev) {
+		drm_dev_unregister(drv_info->drm_dev);
+		drm_dev_unref(drv_info->drm_dev);
+		idr_destroy(&drv_info->idr);
+	}
+	return 0;
+}
+
+static int xen_drm_drv_probe(struct platform_device *pdev)
+{
+	struct xen_drv_info *drv_info;
+	int ret;
+
+	DRM_INFO("Creating %s\n", xen_drm_driver.desc);
+	drv_info = kzalloc(sizeof(*drv_info), GFP_KERNEL);
+	if (!drv_info)
+		return -ENOMEM;
+
+	idr_init(&drv_info->idr);
+	spin_lock_init(&drv_info->idr_lock);
+	spin_lock_init(&drv_info->wait_list_lock);
+	INIT_LIST_HEAD(&drv_info->wait_obj_list);
+
+	/*
+	 * The device is not spawn from a device tree, so arch_setup_dma_ops
+	 * is not called, thus leaving the device with dummy DMA ops.
+	 * This makes the device return error on PRIME buffer import, which
+	 * is not correct: to fix this call of_dma_configure() with a NULL
+	 * node to set default DMA ops.
+	 */
+	of_dma_configure(&pdev->dev, NULL);
+
+	drv_info->drm_dev = drm_dev_alloc(&xen_drm_driver, &pdev->dev);
+	if (!drv_info->drm_dev)
+		return -ENOMEM;
+
+	ret = drm_dev_register(drv_info->drm_dev, 0);
+	if (ret < 0)
+		goto fail;
+
+	drv_info->drm_dev->dev_private = drv_info;
+	platform_set_drvdata(pdev, drv_info);
+
+	DRM_INFO("Initialized %s %d.%d.%d %s on minor %d\n",
+			xen_drm_driver.name, xen_drm_driver.major,
+			xen_drm_driver.minor, xen_drm_driver.patchlevel,
+			xen_drm_driver.date, drv_info->drm_dev->primary->index);
+	return 0;
+
+fail:
+	drm_dev_unref(drv_info->drm_dev);
+	kfree(drv_info);
+	return ret;
+}
+
+static struct platform_driver zcopy_platform_drv_info = {
+	.probe		= xen_drm_drv_probe,
+	.remove		= xen_drm_drv_remove,
+	.driver		= {
+		.name	= XENDRM_ZCOPY_DRIVER_NAME,
+	},
+};
+
+struct platform_device_info zcopy_dev_info = {
+	.name = XENDRM_ZCOPY_DRIVER_NAME,
+	.id = 0,
+	.num_res = 0,
+	.dma_mask = DMA_BIT_MASK(32),
+};
+
+static struct platform_device *xen_pdev;
+
+static int __init xen_drv_init(void)
+{
+	int ret;
+
+	/* At the moment we only support case with XEN_PAGE_SIZE == PAGE_SIZE */
+	if (XEN_PAGE_SIZE != PAGE_SIZE) {
+		DRM_ERROR(XENDRM_ZCOPY_DRIVER_NAME ": different kernel and Xen page sizes are not supported: XEN_PAGE_SIZE (%lu) != PAGE_SIZE (%lu)\n",
+				XEN_PAGE_SIZE, PAGE_SIZE);
+		return -ENODEV;
+	}
+
+	if (!xen_domain())
+		return -ENODEV;
+
+	xen_pdev = platform_device_register_full(&zcopy_dev_info);
+	if (!xen_pdev) {
+		DRM_ERROR("Failed to register " XENDRM_ZCOPY_DRIVER_NAME " device\n");
+		return -ENODEV;
+	}
+
+	ret = platform_driver_register(&zcopy_platform_drv_info);
+	if (ret != 0) {
+		DRM_ERROR("Failed to register " XENDRM_ZCOPY_DRIVER_NAME " driver: %d\n", ret);
+		platform_device_unregister(xen_pdev);
+		return ret;
+	}
+
+	return 0;
+}
+
+static void __exit xen_drv_fini(void)
+{
+	if (xen_pdev)
+		platform_device_unregister(xen_pdev);
+	platform_driver_unregister(&zcopy_platform_drv_info);
+}
+
+module_init(xen_drv_init);
+module_exit(xen_drv_fini);
+
+MODULE_DESCRIPTION("Xen zero-copy helper DRM device");
+MODULE_LICENSE("GPL");
diff --git a/drivers/gpu/drm/xen/xen_drm_zcopy_balloon.c b/drivers/gpu/drm/xen/xen_drm_zcopy_balloon.c
new file mode 100644
index 000000000000..2679233b9f84
--- /dev/null
+++ b/drivers/gpu/drm/xen/xen_drm_zcopy_balloon.c
@@ -0,0 +1,154 @@
+// SPDX-License-Identifier: GPL-2.0 OR MIT
+
+/*
+ *  Xen zero-copy helper DRM device
+ *
+ * Copyright (C) 2016-2018 EPAM Systems Inc.
+ *
+ * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
+ */
+
+#include <drm/drmP.h>
+
+#if defined(CONFIG_DRM_XEN_ZCOPY_CMA)
+#include <asm/xen/hypercall.h>
+#include <xen/interface/memory.h>
+#include <xen/page.h>
+#else
+#include <xen/balloon.h>
+#endif
+
+#include "xen_drm_zcopy_balloon.h"
+
+#if defined(CONFIG_DRM_XEN_ZCOPY_CMA)
+int xen_drm_zcopy_ballooned_pages_alloc(struct device *dev,
+		struct xen_drm_zcopy_balloon *obj, int num_pages,
+		struct page **pages)
+{
+	xen_pfn_t *frame_list;
+	size_t size;
+	int i, ret;
+	dma_addr_t dev_addr, cpu_addr;
+	void *vaddr = NULL;
+	struct xen_memory_reservation reservation = {
+		.address_bits = 0,
+		.extent_order = 0,
+		.domid        = DOMID_SELF
+	};
+
+	size = num_pages * PAGE_SIZE;
+	DRM_DEBUG("Ballooning out %d pages, size %zu\n", num_pages, size);
+	frame_list = kcalloc(num_pages, sizeof(*frame_list), GFP_KERNEL);
+	if (!frame_list)
+		return -ENOMEM;
+
+	vaddr = dma_alloc_wc(dev, size, &dev_addr, GFP_KERNEL | __GFP_NOWARN);
+	if (!vaddr) {
+		DRM_ERROR("Failed to allocate DMA buffer with size %zu\n",
+				size);
+		ret = -ENOMEM;
+		goto fail;
+	}
+
+	cpu_addr = dev_addr;
+	for (i = 0; i < num_pages; i++) {
+		pages[i] = pfn_to_page(__phys_to_pfn(cpu_addr));
+		/*
+		 * XENMEM_populate_physmap requires a PFN based on Xen
+		 * granularity.
+		 */
+		frame_list[i] = page_to_xen_pfn(pages[i]);
+		cpu_addr += PAGE_SIZE;
+	}
+
+	set_xen_guest_handle(reservation.extent_start, frame_list);
+	reservation.nr_extents = num_pages;
+	/* rc will hold number of pages processed */
+	ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
+	if (ret <= 0) {
+		DRM_ERROR("Failed to balloon out %d pages (%d), retrying\n",
+				num_pages, ret);
+		WARN_ON(ret != num_pages);
+		ret = -EFAULT;
+		goto fail;
+	}
+
+	obj->vaddr = vaddr;
+	obj->dev_bus_addr = dev_addr;
+	kfree(frame_list);
+	return 0;
+
+fail:
+	if (vaddr)
+		dma_free_wc(dev, size, vaddr, dev_addr);
+
+	kfree(frame_list);
+	return ret;
+}
+
+void xen_drm_zcopy_ballooned_pages_free(struct device *dev,
+		struct xen_drm_zcopy_balloon *obj, int num_pages,
+		struct page **pages)
+{
+	xen_pfn_t *frame_list;
+	int i, ret;
+	size_t size;
+	struct xen_memory_reservation reservation = {
+		.address_bits = 0,
+		.extent_order = 0,
+		.domid        = DOMID_SELF
+	};
+
+	if (!pages)
+		return;
+
+	if (!obj->vaddr)
+		return;
+
+	frame_list = kcalloc(num_pages, sizeof(*frame_list), GFP_KERNEL);
+	if (!frame_list) {
+		DRM_ERROR("Failed to balloon in %d pages\n", num_pages);
+		return;
+	}
+
+	DRM_DEBUG("Ballooning in %d pages\n", num_pages);
+	size = num_pages * PAGE_SIZE;
+	for (i = 0; i < num_pages; i++) {
+		/*
+		 * XENMEM_populate_physmap requires a PFN based on Xen
+		 * granularity.
+		 */
+		frame_list[i] = page_to_xen_pfn(pages[i]);
+	}
+
+	set_xen_guest_handle(reservation.extent_start, frame_list);
+	reservation.nr_extents = num_pages;
+	/* rc will hold number of pages processed */
+	ret = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
+	if (ret <= 0) {
+		DRM_ERROR("Failed to balloon in %d pages\n", num_pages);
+		WARN_ON(ret != num_pages);
+	}
+
+	if (obj->vaddr)
+		dma_free_wc(dev, size, obj->vaddr, obj->dev_bus_addr);
+
+	obj->vaddr = NULL;
+	obj->dev_bus_addr = 0;
+	kfree(frame_list);
+}
+#else
+int xen_drm_zcopy_ballooned_pages_alloc(struct device *dev,
+		struct xen_drm_zcopy_balloon *obj, int num_pages,
+		struct page **pages)
+{
+	return alloc_xenballooned_pages(num_pages, pages);
+}
+
+void xen_drm_zcopy_ballooned_pages_free(struct device *dev,
+		struct xen_drm_zcopy_balloon *obj, int num_pages,
+		struct page **pages)
+{
+	free_xenballooned_pages(num_pages, pages);
+}
+#endif /* defined(CONFIG_DRM_XEN_ZCOPY_CMA) */
diff --git a/drivers/gpu/drm/xen/xen_drm_zcopy_balloon.h b/drivers/gpu/drm/xen/xen_drm_zcopy_balloon.h
new file mode 100644
index 000000000000..1151f17f9339
--- /dev/null
+++ b/drivers/gpu/drm/xen/xen_drm_zcopy_balloon.h
@@ -0,0 +1,38 @@
+/* SPDX-License-Identifier: GPL-2.0 OR MIT */
+
+/*
+ *  Xen zero-copy helper DRM device
+ *
+ * Copyright (C) 2016-2018 EPAM Systems Inc.
+ *
+ * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
+ */
+
+#ifndef __XEN_DRM_ZCOPY_BALLOON_H_
+#define __XEN_DRM_ZCOPY_BALLOON_H_
+
+#include <linux/types.h>
+
+#ifndef GRANT_INVALID_REF
+/*
+ * Note on usage of grant reference 0 as invalid grant reference:
+ * grant reference 0 is valid, but never exposed to a PV driver,
+ * because of the fact it is already in use/reserved by the PV console.
+ */
+#define GRANT_INVALID_REF	0
+#endif
+
+struct xen_drm_zcopy_balloon {
+	void *vaddr;
+	dma_addr_t dev_bus_addr;
+};
+
+int xen_drm_zcopy_ballooned_pages_alloc(struct device *dev,
+		struct xen_drm_zcopy_balloon *obj, int num_pages,
+		struct page **pages);
+
+void xen_drm_zcopy_ballooned_pages_free(struct device *dev,
+		struct xen_drm_zcopy_balloon *obj, int num_pages,
+		struct page **pages);
+
+#endif /* __XEN_DRM_ZCOPY_BALLOON_H_ */
diff --git a/include/uapi/drm/xen_zcopy_drm.h b/include/uapi/drm/xen_zcopy_drm.h
new file mode 100644
index 000000000000..8767cfbf0350
--- /dev/null
+++ b/include/uapi/drm/xen_zcopy_drm.h
@@ -0,0 +1,129 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+
+/*
+ *  Xen zero-copy helper DRM device
+ *
+ * Copyright (C) 2016-2018 EPAM Systems Inc.
+ *
+ * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
+ */
+#ifndef __XEN_ZCOPY_DRM_H
+#define __XEN_ZCOPY_DRM_H
+
+#include "drm.h"
+
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
+#define XENDRM_ZCOPY_DRIVER_NAME	"xen_drm_zcopy"
+
+/**
+ * DOC: DRM_XEN_ZCOPY_DUMB_FROM_REFS
+ *
+ * This will create a DRM dumb buffer from grant references provided
+ * by the frontend:
+ *
+ * - Frontend
+ *
+ *  - creates a dumb/display buffer and allocates memory.
+ *  - grants foreign access to the buffer pages
+ *  - passes granted references to the backend
+ *
+ * - Backend
+ *
+ *  - issues DRM_XEN_ZCOPY_DUMB_FROM_REFS ioctl to map
+ *    granted references and create a dumb buffer.
+ *  - requests handle to fd conversion via DRM_IOCTL_PRIME_HANDLE_TO_FD
+ *  - requests real HW driver to import the PRIME buffer with
+ *    DRM_IOCTL_PRIME_FD_TO_HANDLE
+ *  - uses handle returned by the real HW driver
+ *
+ *  At the end:
+ *
+ *   - closes real HW driver's handle with DRM_IOCTL_GEM_CLOSE
+ *   - closes zero-copy driver's handle with DRM_IOCTL_GEM_CLOSE
+ *   - closes file descriptor of the exported buffer
+ *   - may wait for the object to be actually freed via wait_handle
+ *     and DRM_XEN_ZCOPY_DUMB_WAIT_FREE
+ */
+#define DRM_XEN_ZCOPY_DUMB_FROM_REFS	0x00
+
+struct drm_xen_zcopy_dumb_from_refs {
+	uint32_t num_grefs;
+	/* user-space uses uint32_t instead of grant_ref_t for mapping */
+	uint32_t *grefs;
+	uint64_t otherend_id;
+	struct drm_mode_create_dumb dumb;
+	uint32_t wait_handle;
+};
+
+/**
+ * DOC: DRM_XEN_ZCOPY_DUMB_TO_REFS
+ *
+ * This will grant references to a dumb/display buffer's memory provided by the
+ * backend:
+ *
+ * - Frontend
+ *
+ *  - requests backend to allocate dumb/display buffer and grant references
+ *    to its pages
+ *
+ * - Backend
+ *
+ *  - requests real HW driver to create a dumb with DRM_IOCTL_MODE_CREATE_DUMB
+ *  - requests handle to fd conversion via DRM_IOCTL_PRIME_HANDLE_TO_FD
+ *  - requests zero-copy driver to import the PRIME buffer with
+ *    DRM_IOCTL_PRIME_FD_TO_HANDLE
+ *  - issues DRM_XEN_ZCOPY_DUMB_TO_REFS ioctl to grant references to the
+ *    buffer's memory.
+ *  - passes grant references to the frontend
+ *
+ *  At the end:
+ *
+ *   - closes zero-copy driver's handle with DRM_IOCTL_GEM_CLOSE
+ *   - closes real HW driver's handle with DRM_IOCTL_GEM_CLOSE
+ *   - closes file descriptor of the imported buffer
+ */
+#define DRM_XEN_ZCOPY_DUMB_TO_REFS	0x01
+
+struct drm_xen_zcopy_dumb_to_refs {
+	uint32_t num_grefs;
+	/* user-space uses uint32_t instead of grant_ref_t for mapping */
+	uint32_t *grefs;
+	uint64_t otherend_id;
+	uint32_t handle;
+};
+
+/**
+ * DOC: DRM_XEN_ZCOPY_DUMB_WAIT_FREE
+ *
+ * This will block until the dumb buffer with the wait handle provided be freed:
+ * this is needed for synchronization between frontend and backend in case
+ * frontend provides grant references of the buffer via
+ * DRM_XEN_ZCOPY_DUMB_FROM_REFS IOCTL and which must be released before
+ * backend replies with XENDISPL_OP_DBUF_DESTROY response.
+ * wait_handle must be the same value returned while calling
+ * DRM_XEN_ZCOPY_DUMB_FROM_REFS IOCTL.
+ */
+#define DRM_XEN_ZCOPY_DUMB_WAIT_FREE	0x02
+
+struct drm_xen_zcopy_dumb_wait_free {
+	uint32_t wait_handle;
+	uint32_t wait_to_ms;
+};
+
+#define DRM_IOCTL_XEN_ZCOPY_DUMB_FROM_REFS DRM_IOWR(DRM_COMMAND_BASE + \
+	DRM_XEN_ZCOPY_DUMB_FROM_REFS, struct drm_xen_zcopy_dumb_from_refs)
+
+#define DRM_IOCTL_XEN_ZCOPY_DUMB_TO_REFS DRM_IOWR(DRM_COMMAND_BASE + \
+	DRM_XEN_ZCOPY_DUMB_TO_REFS, struct drm_xen_zcopy_dumb_to_refs)
+
+#define DRM_IOCTL_XEN_ZCOPY_DUMB_WAIT_FREE DRM_IOWR(DRM_COMMAND_BASE + \
+	DRM_XEN_ZCOPY_DUMB_WAIT_FREE, struct drm_xen_zcopy_dumb_wait_free)
+
+#if defined(__cplusplus)
+}
+#endif
+
+#endif /* __XEN_ZCOPY_DRM_H*/
-- 
2.16.2