Re: [PATCH v2 09/21] drm: panfrost: fix sg_table nents vs. orig_nents misuse
From: Steven Price <steven.price@arm.com>
Date: 2020-05-04 13:28:02
Also in:
dri-devel, linux-iommu, lkml
On 04/05/2020 13:53, Marek Szyprowski wrote:
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.
I find this commit message a bit confusing, but AFAICT the problem with
the Panfrost code is really in mmu_map_sg() where we don't have the
return value from dma_map_sg() and the for_each_sg() loop could (in
theory) run off the end of the list.
The fix seems correct - store the return where it's meant to be (nents)
and make sure when unmapping we use the original (orig_nents). So you
might also consider adding:
Fixes: f3ba91228e8e ("drm/panfrost: Add initial panfrost driver")
Even better would be the wrappers you mention in the cover letter! ;)
Reviewed-by: Steven Price <steven.price@arm.com>
quoted hunk ↗ jump to hunk
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/panfrost/panfrost_gem.c | 3 ++- drivers/gpu/drm/panfrost/panfrost_mmu.c | 4 +++- 2 files changed, 5 insertions(+), 2 deletions(-)diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c index 17b654e..22fec7c 100644 --- a/drivers/gpu/drm/panfrost/panfrost_gem.c +++ b/drivers/gpu/drm/panfrost/panfrost_gem.c@@ -42,7 +42,8 @@ static void panfrost_gem_free_object(struct drm_gem_object *obj) for (i = 0; i < n_sgt; i++) { if (bo->sgts[i].sgl) { dma_unmap_sg(pfdev->dev, bo->sgts[i].sgl, - bo->sgts[i].nents, DMA_BIDIRECTIONAL); + bo->sgts[i].orig_nents, + DMA_BIDIRECTIONAL); sg_free_table(&bo->sgts[i]); } }diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c index ed28aeb..2d9b1f9 100644 --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c@@ -517,7 +517,9 @@ static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as, if (ret) goto err_pages; - if (!dma_map_sg(pfdev->dev, sgt->sgl, sgt->nents, DMA_BIDIRECTIONAL)) { + sgt->nents = dma_map_sg(pfdev->dev, sgt->sgl, sgt->orig_nents, + DMA_BIDIRECTIONAL); + if (!sgt->nents) { ret = -EINVAL; goto err_map; }
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