[PATCH 6/8] xen/gntdev: Implement dma-buf export functionality

[Oleksandr Andrushchenko <andr2000@gmail.com>]

From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>

1. Create a dma-buf from grant references provided by the foreign
   domain. By default dma-buf is backed by system memory pages, but
   by providing GNTDEV_DMA_FLAG_XXX flags it can also be created
   as a DMA write-combine/coherent buffer, e.g. allocated with
   corresponding dma_alloc_xxx API.
   Export the resulting buffer as a new dma-buf.

2. Implement waiting for the dma-buf to be released: block until the
   dma-buf with the file descriptor provided is released.
   If within the time-out provided the buffer is not released then
   -ETIMEDOUT error is returned. If the buffer with the file descriptor
   does not exist or has already been released, then -ENOENT is returned.
   For valid file descriptors this must not be treated as error.

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
---
 drivers/xen/gntdev.c | 478 ++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 476 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 9e450622af1a..52abc6cd5846 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -4,6 +4,8 @@
  * Device for accessing (in user-space) pages that have been granted by other
  * domains.
  *
+ * DMA buffer implementation is based on drivers/gpu/drm/drm_prime.c.
+ *
  * Copyright (c) 2006-2007, D G Murray.
  *           (c) 2009 Gerd Hoffmann <kraxel@redhat.com>
  *           (c) 2018 Oleksandr Andrushchenko, EPAM Systems Inc.
@@ -41,6 +43,9 @@
 #ifdef CONFIG_XEN_GRANT_DMA_ALLOC
 #include <linux/of_device.h>
 #endif
+#ifdef CONFIG_XEN_GNTDEV_DMABUF
+#include <linux/dma-buf.h>
+#endif
 
 #include <xen/xen.h>
 #include <xen/grant_table.h>
@@ -81,6 +86,17 @@ struct gntdev_priv {
 	/* Device for which DMA memory is allocated. */
 	struct device *dma_dev;
 #endif
+
+#ifdef CONFIG_XEN_GNTDEV_DMABUF
+	/* Private data of the hyper DMA buffers. */
+
+	/* List of exported DMA buffers. */
+	struct list_head dmabuf_exp_list;
+	/* List of wait objects. */
+	struct list_head dmabuf_exp_wait_list;
+	/* This is the lock which protects dma_buf_xxx lists. */
+	struct mutex dmabuf_lock;
+#endif
 };
 
 struct unmap_notify {
@@ -125,12 +141,38 @@ struct grant_map {
 
 #ifdef CONFIG_XEN_GNTDEV_DMABUF
 struct xen_dmabuf {
+	struct gntdev_priv *priv;
+	struct dma_buf *dmabuf;
+	struct list_head next;
+	int fd;
+
 	union {
+		struct {
+			/* Exported buffers are reference counted. */
+			struct kref refcount;
+			struct grant_map *map;
+		} exp;
 		struct {
 			/* Granted references of the imported buffer. */
 			grant_ref_t *refs;
 		} imp;
 	} u;
+
+	/* Number of pages this buffer has. */
+	int nr_pages;
+	/* Pages of this buffer. */
+	struct page **pages;
+};
+
+struct xen_dmabuf_wait_obj {
+	struct list_head next;
+	struct xen_dmabuf *xen_dmabuf;
+	struct completion completion;
+};
+
+struct xen_dmabuf_attachment {
+	struct sg_table *sgt;
+	enum dma_data_direction dir;
 };
 #endif
 
@@ -320,6 +362,16 @@ static void gntdev_put_map(struct gntdev_priv *priv, struct grant_map *map)
 	gntdev_free_map(map);
 }
 
+#ifdef CONFIG_XEN_GNTDEV_DMABUF
+static void gntdev_remove_map(struct gntdev_priv *priv, struct grant_map *map)
+{
+	mutex_lock(&priv->lock);
+	list_del(&map->next);
+	gntdev_put_map(NULL /* already removed */, map);
+	mutex_unlock(&priv->lock);
+}
+#endif
+
 /* ------------------------------------------------------------------ */
 
 static int find_grant_ptes(pte_t *pte, pgtable_t token,
@@ -628,6 +680,12 @@ static int gntdev_open(struct inode *inode, struct file *flip)
 	INIT_LIST_HEAD(&priv->freeable_maps);
 	mutex_init(&priv->lock);
 
+#ifdef CONFIG_XEN_GNTDEV_DMABUF
+	mutex_init(&priv->dmabuf_lock);
+	INIT_LIST_HEAD(&priv->dmabuf_exp_list);
+	INIT_LIST_HEAD(&priv->dmabuf_exp_wait_list);
+#endif
+
 	if (use_ptemod) {
 		priv->mm = get_task_mm(current);
 		if (!priv->mm) {
@@ -1053,17 +1111,433 @@ static long gntdev_ioctl_grant_copy(struct gntdev_priv *priv, void __user *u)
 /* DMA buffer export support.                                         */
 /* ------------------------------------------------------------------ */
 
+/* ------------------------------------------------------------------ */
+/* Implementation of wait for exported DMA buffer to be released.     */
+/* ------------------------------------------------------------------ */
+
+static void dmabuf_exp_release(struct kref *kref);
+
+static struct xen_dmabuf_wait_obj *
+dmabuf_exp_wait_obj_new(struct gntdev_priv *priv,
+			struct xen_dmabuf *xen_dmabuf)
+{
+	struct xen_dmabuf_wait_obj *obj;
+
+	obj = kzalloc(sizeof(*obj), GFP_KERNEL);
+	if (!obj)
+		return ERR_PTR(-ENOMEM);
+
+	init_completion(&obj->completion);
+	obj->xen_dmabuf = xen_dmabuf;
+
+	mutex_lock(&priv->dmabuf_lock);
+	list_add(&obj->next, &priv->dmabuf_exp_wait_list);
+	/* Put our reference and wait for xen_dmabuf's release to fire. */
+	kref_put(&xen_dmabuf->u.exp.refcount, dmabuf_exp_release);
+	mutex_unlock(&priv->dmabuf_lock);
+	return obj;
+}
+
+static void dmabuf_exp_wait_obj_free(struct gntdev_priv *priv,
+				     struct xen_dmabuf_wait_obj *obj)
+{
+	struct xen_dmabuf_wait_obj *cur_obj, *q;
+
+	mutex_lock(&priv->dmabuf_lock);
+	list_for_each_entry_safe(cur_obj, q, &priv->dmabuf_exp_wait_list, next)
+		if (cur_obj == obj) {
+			list_del(&obj->next);
+			kfree(obj);
+			break;
+		}
+	mutex_unlock(&priv->dmabuf_lock);
+}
+
+static int dmabuf_exp_wait_obj_wait(struct xen_dmabuf_wait_obj *obj,
+				    u32 wait_to_ms)
+{
+	if (wait_for_completion_timeout(&obj->completion,
+			msecs_to_jiffies(wait_to_ms)) <= 0)
+		return -ETIMEDOUT;
+
+	return 0;
+}
+
+static void dmabuf_exp_wait_obj_signal(struct gntdev_priv *priv,
+				       struct xen_dmabuf *xen_dmabuf)
+{
+	struct xen_dmabuf_wait_obj *obj, *q;
+
+	list_for_each_entry_safe(obj, q, &priv->dmabuf_exp_wait_list, next)
+		if (obj->xen_dmabuf == xen_dmabuf) {
+			pr_debug("Found xen_dmabuf in the wait list, wake\n");
+			complete_all(&obj->completion);
+		}
+}
+
+static struct xen_dmabuf *
+dmabuf_exp_wait_obj_get_by_fd(struct gntdev_priv *priv, int fd)
+{
+	struct xen_dmabuf *q, *xen_dmabuf, *ret = ERR_PTR(-ENOENT);
+
+	mutex_lock(&priv->dmabuf_lock);
+	list_for_each_entry_safe(xen_dmabuf, q, &priv->dmabuf_exp_list, next)
+		if (xen_dmabuf->fd == fd) {
+			pr_debug("Found xen_dmabuf in the wait list\n");
+			kref_get(&xen_dmabuf->u.exp.refcount);
+			ret = xen_dmabuf;
+			break;
+		}
+	mutex_unlock(&priv->dmabuf_lock);
+	return ret;
+}
+
 static int dmabuf_exp_wait_released(struct gntdev_priv *priv, int fd,
 				    int wait_to_ms)
 {
-	return -ETIMEDOUT;
+	struct xen_dmabuf *xen_dmabuf;
+	struct xen_dmabuf_wait_obj *obj;
+	int ret;
+
+	pr_debug("Will wait for dma-buf with fd %d\n", fd);
+	/*
+	 * Try to find the DMA buffer: if not found means that
+	 * either the buffer has already been released or file descriptor
+	 * provided is wrong.
+	 */
+	xen_dmabuf = dmabuf_exp_wait_obj_get_by_fd(priv, fd);
+	if (IS_ERR(xen_dmabuf))
+		return PTR_ERR(xen_dmabuf);
+
+	/*
+	 * xen_dmabuf 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.
+	 */
+	obj = dmabuf_exp_wait_obj_new(priv, xen_dmabuf);
+	if (IS_ERR(obj)) {
+		pr_err("Failed to setup wait object, ret %ld\n", PTR_ERR(obj));
+		return PTR_ERR(obj);
+	}
+
+	ret = dmabuf_exp_wait_obj_wait(obj, wait_to_ms);
+	dmabuf_exp_wait_obj_free(priv, obj);
+	return ret;
+}
+
+/* ------------------------------------------------------------------ */
+/* DMA buffer export support.                                         */
+/* ------------------------------------------------------------------ */
+
+static struct sg_table *
+dmabuf_pages_to_sgt(struct page **pages, unsigned int nr_pages)
+{
+	struct sg_table *sgt;
+	int ret;
+
+	sgt = kmalloc(sizeof(*sgt), GFP_KERNEL);
+	if (!sgt) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	ret = sg_alloc_table_from_pages(sgt, pages, nr_pages, 0,
+					nr_pages << PAGE_SHIFT,
+					GFP_KERNEL);
+	if (ret)
+		goto out;
+
+	return sgt;
+
+out:
+	kfree(sgt);
+	return ERR_PTR(ret);
+}
+
+static int dmabuf_exp_ops_attach(struct dma_buf *dma_buf,
+				 struct device *target_dev,
+				 struct dma_buf_attachment *attach)
+{
+	struct xen_dmabuf_attachment *xen_dmabuf_attach;
+
+	xen_dmabuf_attach = kzalloc(sizeof(*xen_dmabuf_attach), GFP_KERNEL);
+	if (!xen_dmabuf_attach)
+		return -ENOMEM;
+
+	xen_dmabuf_attach->dir = DMA_NONE;
+	attach->priv = xen_dmabuf_attach;
+	/* Might need to pin the pages of the buffer now. */
+	return 0;
+}
+
+static void dmabuf_exp_ops_detach(struct dma_buf *dma_buf,
+				  struct dma_buf_attachment *attach)
+{
+	struct xen_dmabuf_attachment *xen_dmabuf_attach = attach->priv;
+
+	if (xen_dmabuf_attach) {
+		struct sg_table *sgt = xen_dmabuf_attach->sgt;
+
+		if (sgt) {
+			if (xen_dmabuf_attach->dir != DMA_NONE)
+				dma_unmap_sg_attrs(attach->dev, sgt->sgl,
+						   sgt->nents,
+						   xen_dmabuf_attach->dir,
+						   DMA_ATTR_SKIP_CPU_SYNC);
+			sg_free_table(sgt);
+		}
+
+		kfree(sgt);
+		kfree(xen_dmabuf_attach);
+		attach->priv = NULL;
+	}
+	/* Might need to unpin the pages of the buffer now. */
+}
+
+static struct sg_table *
+dmabuf_exp_ops_map_dma_buf(struct dma_buf_attachment *attach,
+			   enum dma_data_direction dir)
+{
+	struct xen_dmabuf_attachment *xen_dmabuf_attach = attach->priv;
+	struct xen_dmabuf *xen_dmabuf = attach->dmabuf->priv;
+	struct sg_table *sgt;
+
+	pr_debug("Mapping %d pages for dev %p\n", xen_dmabuf->nr_pages,
+		 attach->dev);
+
+	if (WARN_ON(dir == DMA_NONE || !xen_dmabuf_attach))
+		return ERR_PTR(-EINVAL);
+
+	/* Return the cached mapping when possible. */
+	if (xen_dmabuf_attach->dir == dir)
+		return xen_dmabuf_attach->sgt;
+
+	/*
+	 * Two mappings with different directions for the same attachment are
+	 * not allowed.
+	 */
+	if (WARN_ON(xen_dmabuf_attach->dir != DMA_NONE))
+		return ERR_PTR(-EBUSY);
+
+	sgt = dmabuf_pages_to_sgt(xen_dmabuf->pages, xen_dmabuf->nr_pages);
+	if (!IS_ERR(sgt)) {
+		if (!dma_map_sg_attrs(attach->dev, sgt->sgl, sgt->nents, dir,
+				      DMA_ATTR_SKIP_CPU_SYNC)) {
+			sg_free_table(sgt);
+			kfree(sgt);
+			sgt = ERR_PTR(-ENOMEM);
+		} else {
+			xen_dmabuf_attach->sgt = sgt;
+			xen_dmabuf_attach->dir = dir;
+		}
+	}
+	if (IS_ERR(sgt))
+		pr_err("Failed to map sg table for dev %p\n", attach->dev);
+	return sgt;
+}
+
+static void dmabuf_exp_ops_unmap_dma_buf(struct dma_buf_attachment *attach,
+					 struct sg_table *sgt,
+					 enum dma_data_direction dir)
+{
+	/* Not implemented. The unmap is done at dmabuf_exp_ops_detach(). */
+}
+
+static void dmabuf_exp_release(struct kref *kref)
+{
+	struct xen_dmabuf *xen_dmabuf =
+		container_of(kref, struct xen_dmabuf, u.exp.refcount);
+
+	dmabuf_exp_wait_obj_signal(xen_dmabuf->priv, xen_dmabuf);
+	list_del(&xen_dmabuf->next);
+	kfree(xen_dmabuf);
+}
+
+static void dmabuf_exp_ops_release(struct dma_buf *dma_buf)
+{
+	struct xen_dmabuf *xen_dmabuf = dma_buf->priv;
+	struct gntdev_priv *priv = xen_dmabuf->priv;
+
+	gntdev_remove_map(priv, xen_dmabuf->u.exp.map);
+	mutex_lock(&priv->dmabuf_lock);
+	kref_put(&xen_dmabuf->u.exp.refcount, dmabuf_exp_release);
+	mutex_unlock(&priv->dmabuf_lock);
+}
+
+static void *dmabuf_exp_ops_kmap_atomic(struct dma_buf *dma_buf,
+					unsigned long page_num)
+{
+	/* Not implemented. */
+	return NULL;
+}
+
+static void dmabuf_exp_ops_kunmap_atomic(struct dma_buf *dma_buf,
+					 unsigned long page_num, void *addr)
+{
+	/* Not implemented. */
+}
+
+static void *dmabuf_exp_ops_kmap(struct dma_buf *dma_buf,
+				 unsigned long page_num)
+{
+	/* Not implemented. */
+	return NULL;
+}
+
+static void dmabuf_exp_ops_kunmap(struct dma_buf *dma_buf,
+				  unsigned long page_num, void *addr)
+{
+	/* Not implemented. */
+}
+
+static int dmabuf_exp_ops_mmap(struct dma_buf *dma_buf,
+			       struct vm_area_struct *vma)
+{
+	/* Not implemented. */
+	return 0;
+}
+
+static const struct dma_buf_ops dmabuf_exp_ops =  {
+	.attach = dmabuf_exp_ops_attach,
+	.detach = dmabuf_exp_ops_detach,
+	.map_dma_buf = dmabuf_exp_ops_map_dma_buf,
+	.unmap_dma_buf = dmabuf_exp_ops_unmap_dma_buf,
+	.release = dmabuf_exp_ops_release,
+	.map = dmabuf_exp_ops_kmap,
+	.map_atomic = dmabuf_exp_ops_kmap_atomic,
+	.unmap = dmabuf_exp_ops_kunmap,
+	.unmap_atomic = dmabuf_exp_ops_kunmap_atomic,
+	.mmap = dmabuf_exp_ops_mmap,
+};
+
+static int dmabuf_export(struct gntdev_priv *priv, struct grant_map *map,
+			 int *fd)
+{
+	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
+	struct xen_dmabuf *xen_dmabuf;
+	int ret = 0;
+
+	xen_dmabuf = kzalloc(sizeof(*xen_dmabuf), GFP_KERNEL);
+	if (!xen_dmabuf)
+		return -ENOMEM;
+
+	kref_init(&xen_dmabuf->u.exp.refcount);
+
+	xen_dmabuf->priv = priv;
+	xen_dmabuf->nr_pages = map->count;
+	xen_dmabuf->pages = map->pages;
+	xen_dmabuf->u.exp.map = map;
+
+	exp_info.exp_name = KBUILD_MODNAME;
+	if (map->dma_dev->driver && map->dma_dev->driver->owner)
+		exp_info.owner = map->dma_dev->driver->owner;
+	else
+		exp_info.owner = THIS_MODULE;
+	exp_info.ops = &dmabuf_exp_ops;
+	exp_info.size = map->count << PAGE_SHIFT;
+	exp_info.flags = O_RDWR;
+	exp_info.priv = xen_dmabuf;
+
+	xen_dmabuf->dmabuf = dma_buf_export(&exp_info);
+	if (IS_ERR(xen_dmabuf->dmabuf)) {
+		ret = PTR_ERR(xen_dmabuf->dmabuf);
+		xen_dmabuf->dmabuf = NULL;
+		goto fail;
+	}
+
+	ret = dma_buf_fd(xen_dmabuf->dmabuf, O_CLOEXEC);
+	if (ret < 0)
+		goto fail;
+
+	xen_dmabuf->fd = ret;
+	*fd = ret;
+
+	pr_debug("Exporting DMA buffer with fd %d\n", ret);
+
+	mutex_lock(&priv->dmabuf_lock);
+	list_add(&xen_dmabuf->next, &priv->dmabuf_exp_list);
+	mutex_unlock(&priv->dmabuf_lock);
+	return 0;
+
+fail:
+	if (xen_dmabuf->dmabuf)
+		dma_buf_put(xen_dmabuf->dmabuf);
+	kfree(xen_dmabuf);
+	return ret;
+}
+
+static struct grant_map *
+dmabuf_exp_alloc_backing_storage(struct gntdev_priv *priv, int dmabuf_flags,
+				 int count)
+{
+	struct grant_map *map;
+
+	if (unlikely(count <= 0))
+		return ERR_PTR(-EINVAL);
+
+	if ((dmabuf_flags & GNTDEV_DMA_FLAG_WC) &&
+	    (dmabuf_flags & GNTDEV_DMA_FLAG_COHERENT)) {
+		pr_err("Wrong dma-buf flags: either WC or coherent, not both\n");
+		return ERR_PTR(-EINVAL);
+	}
+
+	map = gntdev_alloc_map(priv, count, dmabuf_flags);
+	if (!map)
+		return ERR_PTR(-ENOMEM);
+
+	if (unlikely(atomic_add_return(count, &pages_mapped) > limit)) {
+		pr_err("can't map: over limit\n");
+		gntdev_put_map(NULL, map);
+		return ERR_PTR(-ENOMEM);
+	}
+	return map;
 }
 
 static int dmabuf_exp_from_refs(struct gntdev_priv *priv, int flags,
 				int count, u32 domid, u32 *refs, u32 *fd)
 {
+	struct grant_map *map;
+	int i, ret;
+
 	*fd = -1;
-	return -EINVAL;
+
+	if (use_ptemod) {
+		pr_err("Cannot provide dma-buf: use_ptemode %d\n",
+		       use_ptemod);
+		return -EINVAL;
+	}
+
+	map = dmabuf_exp_alloc_backing_storage(priv, flags, count);
+	if (IS_ERR(map))
+		return PTR_ERR(map);
+
+	for (i = 0; i < count; i++) {
+		map->grants[i].domid = domid;
+		map->grants[i].ref = refs[i];
+	}
+
+	mutex_lock(&priv->lock);
+	gntdev_add_map(priv, map);
+	mutex_unlock(&priv->lock);
+
+	map->flags |= GNTMAP_host_map;
+#if defined(CONFIG_X86)
+	map->flags |= GNTMAP_device_map;
+#endif
+
+	ret = map_grant_pages(map);
+	if (ret < 0)
+		goto out;
+
+	ret = dmabuf_export(priv, map, fd);
+	if (ret < 0)
+		goto out;
+
+	return 0;
+
+out:
+	gntdev_remove_map(priv, map);
+	return ret;
 }
 
 /* ------------------------------------------------------------------ */
-- 
2.17.0


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