[PATCH v2 06/21] drm: i915: fix sg_table nents vs. orig_nents misuse for dmabuf objects
From: Marek Szyprowski <m.szyprowski@samsung.com>
Date: 2020-05-04 12:55:41
Also in:
dri-devel, intel-gfx, linux-iommu, lkml
Subsystem:
drm drivers, intel drm i915 driver (meteor lake, dg2 and older excluding poulsbo, moorestown and derivative), the rest · Maintainers:
David Airlie, Simona Vetter, Jani Nikula, Joonas Lahtinen, Rodrigo Vivi, Tvrtko Ursulin, Linus Torvalds
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.
This driver creatively uses sg_table->orig_nents to store the size of the
allocate scatterlist and ignores the number of the entries returned by
dma_map_sg function. The sg_table->orig_nents is (mis)used to properly
free the (over)allocated scatterlist.
This patch only fixes the sg_table->nents entries in the sg_table objects
exported by the dmabuf related functions, so the other drivers, which
might share buffers with i915 could rely on the nents and orig_nents
values.
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
---
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/i915/gem/i915_gem_dmabuf.c | 9 +++++----
drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c | 5 +++--
2 files changed, 8 insertions(+), 6 deletions(-)
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
index 7db5a79..98159df 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c@@ -48,9 +48,10 @@ static struct sg_table *i915_gem_map_dma_buf(struct dma_buf_attachment *attachme src = sg_next(src); } - if (!dma_map_sg_attrs(attachment->dev, - st->sgl, st->nents, dir, - DMA_ATTR_SKIP_CPU_SYNC)) { + st->nents = dma_map_sg_attrs(attachment->dev, + st->sgl, st->orig_nents, dir, + DMA_ATTR_SKIP_CPU_SYNC); + if (!st->nents) { ret = -ENOMEM; goto err_free_sg; }
@@ -74,7 +75,7 @@ static void i915_gem_unmap_dma_buf(struct dma_buf_attachment *attachment, struct drm_i915_gem_object *obj = dma_buf_to_obj(attachment->dmabuf); dma_unmap_sg_attrs(attachment->dev, - sg->sgl, sg->nents, dir, + sg->sgl, sg->orig_nents, dir, DMA_ATTR_SKIP_CPU_SYNC); sg_free_table(sg); kfree(sg);
diff --git a/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c b/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
index debaf7b..5723525 100644
--- a/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
+++ b/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c@@ -28,7 +28,8 @@ static struct sg_table *mock_map_dma_buf(struct dma_buf_attachment *attachment, sg = sg_next(sg); } - if (!dma_map_sg(attachment->dev, st->sgl, st->nents, dir)) { + st->nents = dma_map_sg(attachment->dev, st->sgl, st->orig_nents, dir); + if (!st->nents) { err = -ENOMEM; goto err_st; }
@@ -46,7 +47,7 @@ static void mock_unmap_dma_buf(struct dma_buf_attachment *attachment, struct sg_table *st, enum dma_data_direction dir) { - dma_unmap_sg(attachment->dev, st->sgl, st->nents, dir); + dma_unmap_sg(attachment->dev, st->sgl, st->orig_nents, dir); sg_free_table(st); kfree(st); }
--
1.9.1
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