3 files changed, 63 insertions, 13 deletions

diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-buf-sharing.txt
index 0188903bc9e1..4966b1be42ac 100644
--- a/Documentation/dma-buf-sharing.txt
+++ b/Documentation/dma-buf-sharing.txt
@@ -302,7 +302,11 @@ Access to a dma_buf from the kernel context involves three steps:
       void dma_buf_vunmap(struct dma_buf *dmabuf, void *vaddr)
 
    The vmap call can fail if there is no vmap support in the exporter, or if it
-   runs out of vmalloc space. Fallback to kmap should be implemented.
+   runs out of vmalloc space. Fallback to kmap should be implemented. Note that
+   the dma-buf layer keeps a reference count for all vmap access and calls down
+   into the exporter's vmap function only when no vmapping exists, and only
+   unmaps it once. Protection against concurrent vmap/vunmap calls is provided
+   by taking the dma_buf->lock mutex.
 
 3. Finish access
 
diff --git a/drivers/base/dma-buf.c b/drivers/base/dma-buf.c
index ff5b745c4705..2a7cb0df176b 100644
--- a/drivers/base/dma-buf.c
+++ b/drivers/base/dma-buf.c
@@ -39,6 +39,8 @@ static int dma_buf_release(struct inode *inode, struct file *file)
 
 	dmabuf = file->private_data;
 
+	BUG_ON(dmabuf->vmapping_counter);
+
 	dmabuf->ops->release(dmabuf);
 	kfree(dmabuf);
 	return 0;
@@ -445,6 +447,9 @@ EXPORT_SYMBOL_GPL(dma_buf_kunmap);
 int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma,
 		 unsigned long pgoff)
 {
+	struct file *oldfile;
+	int ret;
+
 	if (WARN_ON(!dmabuf || !vma))
 		return -EINVAL;
 
@@ -458,14 +463,22 @@ int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma,
 		return -EINVAL;
 
 	/* readjust the vma */
-	if (vma->vm_file)
-		fput(vma->vm_file);
-
-	vma->vm_file = get_file(dmabuf->file);
-
+	get_file(dmabuf->file);
+	oldfile = vma->vm_file;
+	vma->vm_file = dmabuf->file;
 	vma->vm_pgoff = pgoff;
 
-	return dmabuf->ops->mmap(dmabuf, vma);
+	ret = dmabuf->ops->mmap(dmabuf, vma);
+	if (ret) {
+		/* restore old parameters on failure */
+		vma->vm_file = oldfile;
+		fput(dmabuf->file);
+	} else {
+		if (oldfile)
+			fput(oldfile);
+	}
+	return ret;
+
 }
 EXPORT_SYMBOL_GPL(dma_buf_mmap);
 
@@ -481,12 +494,34 @@ EXPORT_SYMBOL_GPL(dma_buf_mmap);
  */
 void *dma_buf_vmap(struct dma_buf *dmabuf)
 {
+	void *ptr;
+
 	if (WARN_ON(!dmabuf))
 		return NULL;
 
-	if (dmabuf->ops->vmap)
-		return dmabuf->ops->vmap(dmabuf);
-	return NULL;
+	if (!dmabuf->ops->vmap)
+		return NULL;
+
+	mutex_lock(&dmabuf->lock);
+	if (dmabuf->vmapping_counter) {
+		dmabuf->vmapping_counter++;
+		BUG_ON(!dmabuf->vmap_ptr);
+		ptr = dmabuf->vmap_ptr;
+		goto out_unlock;
+	}
+
+	BUG_ON(dmabuf->vmap_ptr);
+
+	ptr = dmabuf->ops->vmap(dmabuf);
+	if (IS_ERR_OR_NULL(ptr))
+		goto out_unlock;
+
+	dmabuf->vmap_ptr = ptr;
+	dmabuf->vmapping_counter = 1;
+
+out_unlock:
+	mutex_unlock(&dmabuf->lock);
+	return ptr;
 }
 EXPORT_SYMBOL_GPL(dma_buf_vmap);
 
@@ -500,7 +535,16 @@ void dma_buf_vunmap(struct dma_buf *dmabuf, void *vaddr)
 	if (WARN_ON(!dmabuf))
 		return;
 
-	if (dmabuf->ops->vunmap)
-		dmabuf->ops->vunmap(dmabuf, vaddr);
+	BUG_ON(!dmabuf->vmap_ptr);
+	BUG_ON(dmabuf->vmapping_counter == 0);
+	BUG_ON(dmabuf->vmap_ptr != vaddr);
+
+	mutex_lock(&dmabuf->lock);
+	if (--dmabuf->vmapping_counter == 0) {
+		if (dmabuf->ops->vunmap)
+			dmabuf->ops->vunmap(dmabuf, vaddr);
+		dmabuf->vmap_ptr = NULL;
+	}
+	mutex_unlock(&dmabuf->lock);
 }
 EXPORT_SYMBOL_GPL(dma_buf_vunmap);
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index 3d754a394e92..9978b614a1aa 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -119,8 +119,10 @@ struct dma_buf {
 	struct file *file;
 	struct list_head attachments;
 	const struct dma_buf_ops *ops;
-	/* mutex to serialize list manipulation and attach/detach */
+	/* mutex to serialize list manipulation, attach/detach and vmap/unmap */
 	struct mutex lock;
+	unsigned vmapping_counter;
+	void *vmap_ptr;
 	void *priv;
 };