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@xxxxxxxxxxx>
---
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/gpu/drm/radeon/radeon_ttm.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)
diff --git a/drivers/gpu/drm/radeon/radeon_ttm.c b/drivers/gpu/drm/radeon/radeon_ttm.c
index 5d50c9e..166f84e 100644
--- a/drivers/gpu/drm/radeon/radeon_ttm.c
+++ b/drivers/gpu/drm/radeon/radeon_ttm.c
@@ -481,7 +481,7 @@ static int radeon_ttm_tt_pin_userptr(struct ttm_tt *ttm)
{
struct radeon_device *rdev = radeon_get_rdev(ttm->bdev);
struct radeon_ttm_tt *gtt = (void *)ttm;
- unsigned pinned = 0, nents;
+ unsigned pinned = 0;
int r;
int write = !(gtt->userflags & RADEON_GEM_USERPTR_READONLY);
@@ -521,9 +521,8 @@ static int radeon_ttm_tt_pin_userptr(struct ttm_tt *ttm)
if (r)
goto release_sg;
- r = -ENOMEM;
- nents = dma_map_sg(rdev->dev, ttm->sg->sgl, ttm->sg->nents, direction);
- if (nents == 0)
+ r = dma_map_sgtable(rdev->dev, ttm->sg, direction);
+ if (r)
goto release_sg;
drm_prime_sg_to_page_addr_arrays(ttm->sg, ttm->pages,
@@ -554,9 +553,9 @@ static void radeon_ttm_tt_unpin_userptr(struct ttm_tt *ttm)
return;
/* free the sg table and pages again */
- dma_unmap_sg(rdev->dev, ttm->sg->sgl, ttm->sg->nents, direction);
+ dma_unmap_sgtable(rdev->dev, ttm->sg, direction);
- for_each_sg_page(ttm->sg->sgl, &sg_iter, ttm->sg->nents, 0) {
+ for_each_sg_page(ttm->sg->sgl, &sg_iter, ttm->sg->orig_nents, 0) {
struct page *page = sg_page_iter_page(&sg_iter);
if (!(gtt->userflags & RADEON_GEM_USERPTR_READONLY))
set_page_dirty(page);
--
1.9.1
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