[PATCH v2 02/21] drm: amdgpu: fix sg_table nents vs. orig_nents misuse

[Marek Szyprowski]

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 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. Adapt the code to obey those rules.

Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
Reviewed-by: Christian KÃnig <christian.koenig@xxxxxxx>
---
For more information, see '[PATCH v2 00/21] DRM: fix struct sg_table nents
vs. orig_nents misuse' thread: https://lkml.org/lkml/2020/5/4/373
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c | 7 ++++---
 drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c     | 8 ++++----
 2 files changed, 8 insertions(+), 7 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..4df813e 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
@@ -307,8 +307,9 @@ 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))
+		sgt->nents = dma_map_sg_attrs(attach->dev, sgt->sgl, sgt->orig_nents,
+					      dir, DMA_ATTR_SKIP_CPU_SYNC);
+		if (!sgt->nents)
 			goto error_free;
 		break;
 
@@ -349,7 +350,7 @@ 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_sg(attach->dev, sgt->sgl, sgt->orig_nents, dir);
 		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 eff1f73..1f8c507 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -1043,7 +1043,6 @@ 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);
@@ -1059,8 +1058,9 @@ static int amdgpu_ttm_tt_pin_userptr(struct ttm_tt *ttm)
 
 	/* Map SG to device */
 	r = -ENOMEM;
-	nents = dma_map_sg(adev->dev, ttm->sg->sgl, ttm->sg->nents, direction);
-	if (nents == 0)
+	ttm->sg->nents = dma_map_sg(adev->dev, ttm->sg->sgl,
+				    ttm->sg->orig_nents, direction);
+	if (ttm->sg->nents == 0)
 		goto release_sg;
 
 	/* convert SG to linear array of pages and dma addresses */
@@ -1091,7 +1091,7 @@ 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_sg(adev->dev, ttm->sg->sgl, ttm->sg->orig_nents, direction);
 
 	sg_free_table(ttm->sg);
 
-- 
1.9.1