Commit ac80cd17 authored by Jianxin Xiong's avatar Jianxin Xiong Committed by Daniel Vetter
Browse files

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: default avatarJianxin Xiong <jianxin.xiong@intel.com>
Reviewed-by: default avatarChristian König <christian.koenig@amd.com>
Signed-off-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/1602692161-107096-1-git-send-email-jianxin.xiong@intel.com
parent 73b62cdb

drivers/dma-buf/dma-buf.c

+21 −0
Original line number Diff line number Diff line
@@ -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);

include/linux/dma-buf.h

+2 −1
Original line number Diff line number Diff line
@@ -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

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