[PATCH v5 06/38] drm: core: fix common struct sg_table related issues

[Marek Szyprowski]

The Documentation/DMA-API-HOWTO.txt states that the dma_map_sg() function
returns the number of the created entries in the DMA address space.
However the subsequent calls to the dma_sync_sg_for_{device,cpu}() and
dma_unmap_sg must be called with the original number of the entries
passed to the dma_map_sg().

struct sg_table is a common structure used for describing a non-contiguous
memory buffer, used commonly in the DRM and graphics subsystems. It
consists of a scatterlist with memory pages and DMA addresses (sgl entry),
as well as the number of scatterlist entries: CPU pages (orig_nents entry)
and DMA mapped pages (nents entry).

It turned out that it was a common mistake to misuse nents and orig_nents
entries, calling DMA-mapping functions with a wrong number of entries or
ignoring the number of mapped entries returned by the dma_map_sg()
function.

To avoid such issues, lets use a common dma-mapping wrappers operating
directly on the struct sg_table objects and use scatterlist page
iterators where possible. This, almost always, hides references to the
nents and orig_nents entries, making the code robust, easier to follow
and copy/paste safe.

Signed-off-by: Marek Szyprowski <m.szyprowski at samsung.com>
---
For more information, see '[PATCH v5 00/38] DRM: fix struct sg_table nents
vs. orig_nents misuse' thread:
https://lore.kernel.org/linux-iommu/20200513132114.6046-1-m.szyprowski@samsung.com/T/
---
 drivers/gpu/drm/drm_cache.c            |  2 +-
 drivers/gpu/drm/drm_gem_shmem_helper.c | 14 +++++++++-----
 drivers/gpu/drm/drm_prime.c            | 11 ++++++-----
 3 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/drm_cache.c b/drivers/gpu/drm/drm_cache.c
index 03e01b0..0fe3c49 100644
--- a/drivers/gpu/drm/drm_cache.c
+++ b/drivers/gpu/drm/drm_cache.c
@@ -127,7 +127,7 @@ static void drm_cache_flush_clflush(struct page *pages[],
 		struct sg_page_iter sg_iter;
 
 		mb(); /*CLFLUSH is ordered only by using memory barriers*/
-		for_each_sg_page(st->sgl, &sg_iter, st->nents, 0)
+		for_each_sgtable_page(st, &sg_iter, 0)
 			drm_clflush_page(sg_page_iter_page(&sg_iter));
 		mb(); /*Make sure that all cache line entry is flushed*/
 
diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index df31e57..00a43e8 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -117,8 +117,8 @@ void drm_gem_shmem_free_object(struct drm_gem_object *obj)
 		kvfree(shmem->pages);
 	} else {
 		if (shmem->sgt) {
-			dma_unmap_sg(obj->dev->dev, shmem->sgt->sgl,
-				     shmem->sgt->nents, DMA_BIDIRECTIONAL);
+			dma_unmap_sgtable(obj->dev->dev, shmem->sgt,
+					  DMA_BIDIRECTIONAL, 0);
 			sg_free_table(shmem->sgt);
 			kfree(shmem->sgt);
 		}
@@ -395,8 +395,7 @@ void drm_gem_shmem_purge_locked(struct drm_gem_object *obj)
 
 	WARN_ON(!drm_gem_shmem_is_purgeable(shmem));
 
-	dma_unmap_sg(obj->dev->dev, shmem->sgt->sgl,
-		     shmem->sgt->nents, DMA_BIDIRECTIONAL);
+	dma_unmap_sgtable(obj->dev->dev, shmem->sgt, DMA_BIDIRECTIONAL, 0);
 	sg_free_table(shmem->sgt);
 	kfree(shmem->sgt);
 	shmem->sgt = NULL;
@@ -623,12 +622,17 @@ struct sg_table *drm_gem_shmem_get_pages_sgt(struct drm_gem_object *obj)
 		goto err_put_pages;
 	}
 	/* Map the pages for use by the h/w. */
-	dma_map_sg(obj->dev->dev, sgt->sgl, sgt->nents, DMA_BIDIRECTIONAL);
+	ret = dma_map_sgtable(obj->dev->dev, sgt, DMA_BIDIRECTIONAL, 0);
+	if (ret)
+		goto err_free_sgt;
 
 	shmem->sgt = sgt;
 
 	return sgt;
 
+err_free_sgt:
+	sg_free_table(sgt);
+	kfree(sgt);
 err_put_pages:
 	drm_gem_shmem_put_pages(shmem);
 	return ERR_PTR(ret);
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index dfdf4d4..5ed22dd 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -617,6 +617,7 @@ struct sg_table *drm_gem_map_dma_buf(struct dma_buf_attachment *attach,
 {
 	struct drm_gem_object *obj = attach->dmabuf->priv;
 	struct sg_table *sgt;
+	int ret;
 
 	if (WARN_ON(dir == DMA_NONE))
 		return ERR_PTR(-EINVAL);
@@ -626,11 +627,12 @@ struct sg_table *drm_gem_map_dma_buf(struct dma_buf_attachment *attach,
 	else
 		sgt = obj->dev->driver->gem_prime_get_sg_table(obj);
 
-	if (!dma_map_sg_attrs(attach->dev, sgt->sgl, sgt->nents, dir,
-			      DMA_ATTR_SKIP_CPU_SYNC)) {
+	ret = dma_map_sgtable(attach->dev, sgt, dir,
+			      DMA_ATTR_SKIP_CPU_SYNC);
+	if (ret) {
 		sg_free_table(sgt);
 		kfree(sgt);
-		sgt = ERR_PTR(-ENOMEM);
+		sgt = ERR_PTR(ret);
 	}
 
 	return sgt;
@@ -652,8 +654,7 @@ void drm_gem_unmap_dma_buf(struct dma_buf_attachment *attach,
 	if (!sgt)
 		return;
 
-	dma_unmap_sg_attrs(attach->dev, sgt->sgl, sgt->nents, dir,
-			   DMA_ATTR_SKIP_CPU_SYNC);
+	dma_unmap_sgtable(attach->dev, sgt, dir, DMA_ATTR_SKIP_CPU_SYNC);
 	sg_free_table(sgt);
 	kfree(sgt);
 }
-- 
1.9.1