On Wed, Oct 14, 2020 at 09:16:01AM -0700, Jianxin Xiong wrote:
> 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@xxxxxxxxx>
lgtm, thanks for creating this and giving it a spin.
I'll queue this up in drm-misc-next for 5.11, should show up in linux-next
after the merge window is closed.
Cheers, Daniel
> ---
> drivers/dma-buf/dma-buf.c | 21 +++++++++++++++++++++
> include/linux/dma-buf.h | 3 ++-
> 2 files changed, 23 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 844967f..7309c83 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -851,6 +851,9 @@ void dma_buf_unpin(struct dma_buf_attachment *attach)
> * 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
> @@ -904,6 +907,24 @@ 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 a2ca294e..4a5fa70 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -145,7 +145,8 @@ 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
> --
> 1.8.3.1
>
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--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
