Merge tag 'tag-for-linus-3.5' of git://git.linaro.org/people/sumitsemwal/linux-dma-buf

Pull dma-buf updates from Sumit Semwal:
"Here's the first signed-tag pull request for dma-buf framework. It
includes the following key items:
- mmap support
- vmap support
- related documentation updates

These are needed by various drivers to allow mmap/vmap of dma-buf
shared buffers. Dave Airlie has some prime patches dependent on the
vmap pull as well."

* tag 'tag-for-linus-3.5' of git://git.linaro.org/people/sumitsemwal/linux-dma-buf:
dma-buf: add initial vmap documentation
dma-buf: minor documentation fixes.
dma-buf: add vmap interface
dma-buf: mmap support

Documentation/dma-buf-sharing.txt

···
    in memory, mapped into its own address space, so it can access the same area
    of memory.
 
-*IMPORTANT*: [see https://lkml.org/lkml/2011/12/20/211 for more details]
-For this first version, A buffer shared using the dma_buf sharing API:
-- *may* be exported to user space using "mmap" *ONLY* by exporter, outside of
-  this framework.
-- with this new iteration of the dma-buf api cpu access from the kernel has been
-  enable, see below for the details.
-
 dma-buf operations for device dma only
 --------------------------------------
 
···
    Note that these calls need to always succeed. The exporter needs to complete
    any preparations that might fail in begin_cpu_access.
 
+   For some cases the overhead of kmap can be too high, a vmap interface
+   is introduced. This interface should be used very carefully, as vmalloc
+   space is a limited resources on many architectures.
+
+   Interfaces:
+      void *dma_buf_vmap(struct dma_buf *dmabuf)
+      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.
+
 3. Finish access
 
    When the importer is done accessing the range specified in begin_cpu_access,
···
 				  size_t start, size_t len,
 				  enum dma_data_direction dir);
 
+
+Direct Userspace Access/mmap Support
+------------------------------------
+
+Being able to mmap an export dma-buf buffer object has 2 main use-cases:
+- CPU fallback processing in a pipeline and
+- supporting existing mmap interfaces in importers.
+
+1. CPU fallback processing in a pipeline
+
+   In many processing pipelines it is sometimes required that the cpu can access
+   the data in a dma-buf (e.g. for thumbnail creation, snapshots, ...). To avoid
+   the need to handle this specially in userspace frameworks for buffer sharing
+   it's ideal if the dma_buf fd itself can be used to access the backing storage
+   from userspace using mmap.
+
+   Furthermore Android's ION framework already supports this (and is otherwise
+   rather similar to dma-buf from a userspace consumer side with using fds as
+   handles, too). So it's beneficial to support this in a similar fashion on
+   dma-buf to have a good transition path for existing Android userspace.
+
+   No special interfaces, userspace simply calls mmap on the dma-buf fd.
+
+2. Supporting existing mmap interfaces in exporters
+
+   Similar to the motivation for kernel cpu access it is again important that
+   the userspace code of a given importing subsystem can use the same interfaces
+   with a imported dma-buf buffer object as with a native buffer object. This is
+   especially important for drm where the userspace part of contemporary OpenGL,
+   X, and other drivers is huge, and reworking them to use a different way to
+   mmap a buffer rather invasive.
+
+   The assumption in the current dma-buf interfaces is that redirecting the
+   initial mmap is all that's needed. A survey of some of the existing
+   subsystems shows that no driver seems to do any nefarious thing like syncing
+   up with outstanding asynchronous processing on the device or allocating
+   special resources at fault time. So hopefully this is good enough, since
+   adding interfaces to intercept pagefaults and allow pte shootdowns would
+   increase the complexity quite a bit.
+
+   Interface:
+      int dma_buf_mmap(struct dma_buf *, struct vm_area_struct *,
+		       unsigned long);
+
+   If the importing subsystem simply provides a special-purpose mmap call to set
+   up a mapping in userspace, calling do_mmap with dma_buf->file will equally
+   achieve that for a dma-buf object.
+
+3. Implementation notes for exporters
+
+   Because dma-buf buffers have invariant size over their lifetime, the dma-buf
+   core checks whether a vma is too large and rejects such mappings. The
+   exporter hence does not need to duplicate this check.
+
+   Because existing importing subsystems might presume coherent mappings for
+   userspace, the exporter needs to set up a coherent mapping. If that's not
+   possible, it needs to fake coherency by manually shooting down ptes when
+   leaving the cpu domain and flushing caches at fault time. Note that all the
+   dma_buf files share the same anon inode, hence the exporter needs to replace
+   the dma_buf file stored in vma->vm_file with it's own if pte shootdown is
+   requred. This is because the kernel uses the underlying inode's address_space
+   for vma tracking (and hence pte tracking at shootdown time with
+   unmap_mapping_range).
+
+   If the above shootdown dance turns out to be too expensive in certain
+   scenarios, we can extend dma-buf with a more explicit cache tracking scheme
+   for userspace mappings. But the current assumption is that using mmap is
+   always a slower path, so some inefficiencies should be acceptable.
+
+   Exporters that shoot down mappings (for any reasons) shall not do any
+   synchronization at fault time with outstanding device operations.
+   Synchronization is an orthogonal issue to sharing the backing storage of a
+   buffer and hence should not be handled by dma-buf itself. This is explictly
+   mentioned here because many people seem to want something like this, but if
+   different exporters handle this differently, buffer sharing can fail in
+   interesting ways depending upong the exporter (if userspace starts depending
+   upon this implicit synchronization).
 
 Miscellaneous notes
 -------------------
···
   flag be set when the dma-buf fd is created.  So any API provided by
   the exporting driver to create a dmabuf fd must provide a way to let
   userspace control setting of O_CLOEXEC flag passed in to dma_buf_fd().
+
+- If an exporter needs to manually flush caches and hence needs to fake
+  coherency for mmap support, it needs to be able to zap all the ptes pointing
+  at the backing storage. Now linux mm needs a struct address_space associated
+  with the struct file stored in vma->vm_file to do that with the function
+  unmap_mapping_range. But the dma_buf framework only backs every dma_buf fd
+  with the anon_file struct file, i.e. all dma_bufs share the same file.
+
+  Hence exporters need to setup their own file (and address_space) association
+  by setting vma->vm_file and adjusting vma->vm_pgoff in the dma_buf mmap
+  callback. In the specific case of a gem driver the exporter could use the
+  shmem file already provided by gem (and set vm_pgoff = 0). Exporters can then
+  zap ptes by unmapping the corresponding range of the struct address_space
+  associated with their own file.
 
 References:
 [1] struct dma_buf_ops in include/linux/dma-buf.h

drivers/base/dma-buf.c

···
 	return 0;
 }
 
+static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma)
+{
+	struct dma_buf *dmabuf;
+
+	if (!is_dma_buf_file(file))
+		return -EINVAL;
+
+	dmabuf = file->private_data;
+
+	/* check for overflowing the buffer's size */
+	if (vma->vm_pgoff + ((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) >
+	    dmabuf->size >> PAGE_SHIFT)
+		return -EINVAL;
+
+	return dmabuf->ops->mmap(dmabuf, vma);
+}
+
 static const struct file_operations dma_buf_fops = {
 	.release	= dma_buf_release,
+	.mmap		= dma_buf_mmap_internal,
 };
 
 /*
···
 			  || !ops->unmap_dma_buf
 			  || !ops->release
 			  || !ops->kmap_atomic
-			  || !ops->kmap)) {
+			  || !ops->kmap
+			  || !ops->mmap)) {
 		return ERR_PTR(-EINVAL);
 	}
 
···
 		dmabuf->ops->kunmap(dmabuf, page_num, vaddr);
 }
 EXPORT_SYMBOL_GPL(dma_buf_kunmap);
+
+
+/**
+ * dma_buf_mmap - Setup up a userspace mmap with the given vma
+ * @dmabuf:	[in]	buffer that should back the vma
+ * @vma:	[in]	vma for the mmap
+ * @pgoff:	[in]	offset in pages where this mmap should start within the
+ * 			dma-buf buffer.
+ *
+ * This function adjusts the passed in vma so that it points at the file of the
+ * dma_buf operation. It alsog adjusts the starting pgoff and does bounds
+ * checking on the size of the vma. Then it calls the exporters mmap function to
+ * set up the mapping.
+ *
+ * Can return negative error values, returns 0 on success.
+ */
+int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma,
+		 unsigned long pgoff)
+{
+	if (WARN_ON(!dmabuf || !vma))
+		return -EINVAL;
+
+	/* check for offset overflow */
+	if (pgoff + ((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) < pgoff)
+		return -EOVERFLOW;
+
+	/* check for overflowing the buffer's size */
+	if (pgoff + ((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) >
+	    dmabuf->size >> PAGE_SHIFT)
+		return -EINVAL;
+
+	/* readjust the vma */
+	if (vma->vm_file)
+		fput(vma->vm_file);
+
+	vma->vm_file = dmabuf->file;
+	get_file(vma->vm_file);
+
+	vma->vm_pgoff = pgoff;
+
+	return dmabuf->ops->mmap(dmabuf, vma);
+}
+EXPORT_SYMBOL_GPL(dma_buf_mmap);
+
+/**
+ * dma_buf_vmap - Create virtual mapping for the buffer object into kernel
+ * address space. Same restrictions as for vmap and friends apply.
+ * @dmabuf:	[in]	buffer to vmap
+ *
+ * This call may fail due to lack of virtual mapping address space.
+ * These calls are optional in drivers. The intended use for them
+ * is for mapping objects linear in kernel space for high use objects.
+ * Please attempt to use kmap/kunmap before thinking about these interfaces.
+ */
+void *dma_buf_vmap(struct dma_buf *dmabuf)
+{
+	if (WARN_ON(!dmabuf))
+		return NULL;
+
+	if (dmabuf->ops->vmap)
+		return dmabuf->ops->vmap(dmabuf);
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(dma_buf_vmap);
+
+/**
+ * dma_buf_vunmap - Unmap a vmap obtained by dma_buf_vmap.
+ * @dmabuf:	[in]	buffer to vunmap
+ */
+void dma_buf_vunmap(struct dma_buf *dmabuf, void *vaddr)
+{
+	if (WARN_ON(!dmabuf))
+		return;
+
+	if (dmabuf->ops->vunmap)
+		dmabuf->ops->vunmap(dmabuf, vaddr);
+}
+EXPORT_SYMBOL_GPL(dma_buf_vunmap);

include/linux/dma-buf.h

···
  * 		   This Callback must not sleep.
  * @kmap: maps a page from the buffer into kernel address space.
  * @kunmap: [optional] unmaps a page from the buffer.
+ * @mmap: used to expose the backing storage to userspace. Note that the
+ * 	  mapping needs to be coherent - if the exporter doesn't directly
+ * 	  support this, it needs to fake coherency by shooting down any ptes
+ * 	  when transitioning away from the cpu domain.
+ * @vmap: [optional] creates a virtual mapping for the buffer into kernel
+ *	  address space. Same restrictions as for vmap and friends apply.
+ * @vunmap: [optional] unmaps a vmap from the buffer
  */
 struct dma_buf_ops {
 	int (*attach)(struct dma_buf *, struct device *,
···
 	void (*kunmap_atomic)(struct dma_buf *, unsigned long, void *);
 	void *(*kmap)(struct dma_buf *, unsigned long);
 	void (*kunmap)(struct dma_buf *, unsigned long, void *);
+
+	int (*mmap)(struct dma_buf *, struct vm_area_struct *vma);
+
+	void *(*vmap)(struct dma_buf *);
+	void (*vunmap)(struct dma_buf *, void *vaddr);
 };
 
 /**
···
 void dma_buf_kunmap_atomic(struct dma_buf *, unsigned long, void *);
 void *dma_buf_kmap(struct dma_buf *, unsigned long);
 void dma_buf_kunmap(struct dma_buf *, unsigned long, void *);
+
+int dma_buf_mmap(struct dma_buf *, struct vm_area_struct *,
+		 unsigned long);
+void *dma_buf_vmap(struct dma_buf *);
+void dma_buf_vunmap(struct dma_buf *, void *vaddr);
 #else
 
 static inline struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
···
 
 static inline void dma_buf_kunmap(struct dma_buf *dmabuf,
 				  unsigned long pnum, void *vaddr)
+{
+}
+
+static inline int dma_buf_mmap(struct dma_buf *dmabuf,
+			       struct vm_area_struct *vma,
+			       unsigned long pgoff)
+{
+	return -ENODEV;
+}
+
+static inline void *dma_buf_vmap(struct dma_buf *dmabuf)
+{
+	return NULL;
+}
+
+static inline void dma_buf_vunmap(struct dma_buf *dmabuf, void *vaddr)
 {
 }
 #endif /* CONFIG_DMA_SHARED_BUFFER */