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



From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>

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@xxxxxxxx>
---
 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@xxxxxxxxxx>
  *           (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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