The Documentation/DMA-API-HOWTO.txt states that dma_map_sg returns the numer of the created entries in the DMA address space. However the subsequent calls to dma_sync_sg_for_{device,cpu} and dma_unmap_sg must be called with the original number of the entries passed to dma_map_sg. The sg_table->nents in turn holds the result of the dma_map_sg call as stated in include/linux/scatterlist.h. A common mistake was to ignore a result of the dma_map_sg function and don't use the sg_table->orig_nents at all.
To avoid such issues, lets use common dma-mapping wrappers operating directly on the struct sg_table objects and adjust references to the nents and orig_nents respectively.
Signed-off-by: Marek Szyprowski m.szyprowski@samsung.com --- For more information, see '[PATCH v3 00/25] DRM: fix struct sg_table nents vs. orig_nents misuse' thread: https://lkml.org/lkml/2020/5/5/187 --- drivers/xen/gntdev-dmabuf.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-)
diff --git a/drivers/xen/gntdev-dmabuf.c b/drivers/xen/gntdev-dmabuf.c index 75d3bb9..4b22785 100644 --- a/drivers/xen/gntdev-dmabuf.c +++ b/drivers/xen/gntdev-dmabuf.c @@ -247,8 +247,7 @@ static void dmabuf_exp_ops_detach(struct dma_buf *dma_buf,
if (sgt) { if (gntdev_dmabuf_attach->dir != DMA_NONE) - dma_unmap_sg_attrs(attach->dev, sgt->sgl, - sgt->nents, + dma_unmap_sgtable_attrs(attach->dev, sgt, gntdev_dmabuf_attach->dir, DMA_ATTR_SKIP_CPU_SYNC); sg_free_table(sgt); @@ -288,7 +287,7 @@ static void dmabuf_exp_ops_detach(struct dma_buf *dma_buf, sgt = dmabuf_pages_to_sgt(gntdev_dmabuf->pages, gntdev_dmabuf->nr_pages); if (!IS_ERR(sgt)) { - if (!dma_map_sg_attrs(attach->dev, sgt->sgl, sgt->nents, dir, + if (dma_map_sgtable_attrs(attach->dev, sgt, dir, DMA_ATTR_SKIP_CPU_SYNC)) { sg_free_table(sgt); kfree(sgt); @@ -625,7 +624,7 @@ static struct gntdev_dmabuf *dmabuf_imp_alloc_storage(int count)
/* Now convert sgt to array of pages and check for page validity. */ i = 0; - for_each_sg_page(sgt->sgl, &sg_iter, sgt->nents, 0) { + for_each_sg_page(sgt->sgl, &sg_iter, sgt->orig_nents, 0) { struct page *page = sg_page_iter_page(&sg_iter); /* * Check if page is valid: this can happen if we are given