dma-buf: Clarify that dma-buf sg lists are page aligned

The dma-buf API have been used under the assumption that the sg lists
returned from dma_buf_map_attachment() are fully page aligned. Lots of
stuff can break otherwise all over the place. Clarify this in the
documentation and add a check when DMA API debug is enabled.

Signed-off-by: Jianxin Xiong <jianxin.xiong@intel.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/1602692161-107096-1-git-send-email-jianxin.xiong@intel.com

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index a6ba4d5..9db211a 100644 (file)
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -849,6 +849,9 @@ EXPORT_SYMBOL_GPL(dma_buf_unpin);
  * Returns sg_table containing the scatterlist to be returned; returns ERR_PTR
  * on error. May return -EINTR if it is interrupted by a signal.
  *
+ * On success, the DMA addresses and lengths in the returned scatterlist are
+ * PAGE_SIZE aligned.
+ *
  * A mapping must be unmapped by using dma_buf_unmap_attachment(). Note that
  * the underlying backing storage is pinned for as long as a mapping exists,
  * therefore users/importers should not hold onto a mapping for undue amounts of
@@ -902,6 +905,24 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
                attach->dir = direction;
        }
 
+#ifdef CONFIG_DMA_API_DEBUG
+       {
+               struct scatterlist *sg;
+               u64 addr;
+               int len;
+               int i;
+
+               for_each_sgtable_dma_sg(sg_table, sg, i) {
+                       addr = sg_dma_address(sg);
+                       len = sg_dma_len(sg);
+                       if (!PAGE_ALIGNED(addr) || !PAGE_ALIGNED(len)) {
+                               pr_debug("%s: addr %llx or len %x is not page aligned!\n",
+                                        __func__, addr, len);
+                       }
+               }
+       }
+#endif /* CONFIG_DMA_API_DEBUG */
+
        return sg_table;
 }
 EXPORT_SYMBOL_GPL(dma_buf_map_attachment);

diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index cf77cc1..03875ea 100644 (file)
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -146,7 +146,8 @@ struct dma_buf_ops {
         *
         * A &sg_table scatter list of or the backing storage of the DMA buffer,
         * already mapped into the device address space of the &device attached
-        * with the provided &dma_buf_attachment.
+        * with the provided &dma_buf_attachment. The addresses and lengths in
+        * the scatter list are PAGE_SIZE aligned.
         *
         * On failure, returns a negative error value wrapped into a pointer.
         * May also return -EINTR when a signal was received while being