[PATCH v4 07/38] drm: amdgpu: 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@xxxxxxxxxxx>
Reviewed-by: Christian KÃnig <christian.koenig@xxxxxxx>
---
For more information, see '[PATCH v4 00/38] DRM: fix struct sg_table nents
vs. orig_nents misuse' thread:
https://lore.kernel.org/dri-devel/20200512085710.14688-1-m.szyprowski@xxxxxxxxxxx/T/
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c  | 6 +++---
 drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c      | 9 +++------
 drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c | 8 ++++----
 3 files changed, 10 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
index 43d8ed7..519ce44 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
@@ -307,8 +307,8 @@ static struct sg_table *amdgpu_dma_buf_map(struct dma_buf_attachment *attach,
 		if (IS_ERR(sgt))
 			return sgt;
 
-		if (!dma_map_sg_attrs(attach->dev, sgt->sgl, sgt->nents, dir,
-				      DMA_ATTR_SKIP_CPU_SYNC))
+		if (dma_map_sgtable(attach->dev, sgt, dir,
+				    DMA_ATTR_SKIP_CPU_SYNC))
 			goto error_free;
 		break;
 
@@ -349,7 +349,7 @@ static void amdgpu_dma_buf_unmap(struct dma_buf_attachment *attach,
 	struct amdgpu_device *adev = amdgpu_ttm_adev(bo->tbo.bdev);
 
 	if (sgt->sgl->page_link) {
-		dma_unmap_sg(attach->dev, sgt->sgl, sgt->nents, dir);
+		dma_unmap_sgtable(attach->dev, sgt, dir, 0);
 		sg_free_table(sgt);
 		kfree(sgt);
 	} else {
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
index 9cbecd5..57a5d56 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -1024,7 +1024,6 @@ static int amdgpu_ttm_tt_pin_userptr(struct ttm_tt *ttm)
 {
 	struct amdgpu_device *adev = amdgpu_ttm_adev(ttm->bdev);
 	struct amdgpu_ttm_tt *gtt = (void *)ttm;
-	unsigned nents;
 	int r;
 
 	int write = !(gtt->userflags & AMDGPU_GEM_USERPTR_READONLY);
@@ -1039,9 +1038,8 @@ static int amdgpu_ttm_tt_pin_userptr(struct ttm_tt *ttm)
 		goto release_sg;
 
 	/* Map SG to device */
-	r = -ENOMEM;
-	nents = dma_map_sg(adev->dev, ttm->sg->sgl, ttm->sg->nents, direction);
-	if (nents == 0)
+	r = dma_map_sgtable(adev->dev, ttm->sg, direction, 0);
+	if (r)
 		goto release_sg;
 
 	/* convert SG to linear array of pages and dma addresses */
@@ -1072,8 +1070,7 @@ static void amdgpu_ttm_tt_unpin_userptr(struct ttm_tt *ttm)
 		return;
 
 	/* unmap the pages mapped to the device */
-	dma_unmap_sg(adev->dev, ttm->sg->sgl, ttm->sg->nents, direction);
-
+	dma_unmap_sgtable(adev->dev, ttm->sg, direction, 0);
 	sg_free_table(ttm->sg);
 
 #if IS_ENABLED(CONFIG_DRM_AMDGPU_USERPTR)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
index d399e58..75495a7 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
@@ -477,11 +477,11 @@ int amdgpu_vram_mgr_alloc_sgt(struct amdgpu_device *adev,
 	if (r)
 		goto error_free;
 
-	for_each_sg((*sgt)->sgl, sg, num_entries, i)
+	for_each_sgtable_sg(*sgt, sg, i)
 		sg->length = 0;
 
 	node = mem->mm_node;
-	for_each_sg((*sgt)->sgl, sg, num_entries, i) {
+	for_each_sgtable_sg(*sgt, sg, i) {
 		phys_addr_t phys = (node->start << PAGE_SHIFT) +
 			adev->gmc.aper_base;
 		size_t size = node->size << PAGE_SHIFT;
@@ -501,7 +501,7 @@ int amdgpu_vram_mgr_alloc_sgt(struct amdgpu_device *adev,
 	return 0;
 
 error_unmap:
-	for_each_sg((*sgt)->sgl, sg, num_entries, i) {
+	for_each_sgtable_sg(*sgt, sg, i) {
 		if (!sg->length)
 			continue;
 
@@ -532,7 +532,7 @@ void amdgpu_vram_mgr_free_sgt(struct amdgpu_device *adev,
 	struct scatterlist *sg;
 	int i;
 
-	for_each_sg(sgt->sgl, sg, sgt->nents, i)
+	for_each_sgtable_sg(sgt, sg, i)
 		dma_unmap_resource(dev, sg->dma_address,
 				   sg->length, dir,
 				   DMA_ATTR_SKIP_CPU_SYNC);
-- 
1.9.1