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    Subject[PATCH v2 12/21] drm: tegra: fix sg_table nents vs. orig_nents misuse
    Date
    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@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/tegra/gem.c | 25 +++++++++++++------------
    drivers/gpu/drm/tegra/plane.c | 13 +++++++------
    2 files changed, 20 insertions(+), 18 deletions(-)

    diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
    index 6237681..5710ab4 100644
    --- a/drivers/gpu/drm/tegra/gem.c
    +++ b/drivers/gpu/drm/tegra/gem.c
    @@ -98,8 +98,8 @@ static struct sg_table *tegra_bo_pin(struct device *dev, struct host1x_bo *bo,
    * the SG table needs to be copied to avoid overwriting any
    * other potential users of the original SG table.
    */
    - err = sg_alloc_table_from_sg(sgt, obj->sgt->sgl, obj->sgt->nents,
    - GFP_KERNEL);
    + err = sg_alloc_table_from_sg(sgt, obj->sgt->sgl,
    + obj->sgt->orig_nents, GFP_KERNEL);
    if (err < 0)
    goto free;
    } else {
    @@ -197,7 +197,7 @@ static int tegra_bo_iommu_map(struct tegra_drm *tegra, struct tegra_bo *bo)
    bo->iova = bo->mm->start;

    bo->size = iommu_map_sg(tegra->domain, bo->iova, bo->sgt->sgl,
    - bo->sgt->nents, prot);
    + bo->sgt->orig_nents, prot);
    if (!bo->size) {
    dev_err(tegra->drm->dev, "failed to map buffer\n");
    err = -ENOMEM;
    @@ -264,7 +264,7 @@ static struct tegra_bo *tegra_bo_alloc_object(struct drm_device *drm,
    static void tegra_bo_free(struct drm_device *drm, struct tegra_bo *bo)
    {
    if (bo->pages) {
    - dma_unmap_sg(drm->dev, bo->sgt->sgl, bo->sgt->nents,
    + dma_unmap_sg(drm->dev, bo->sgt->sgl, bo->sgt->orig_nents,
    DMA_FROM_DEVICE);
    drm_gem_put_pages(&bo->gem, bo->pages, true, true);
    sg_free_table(bo->sgt);
    @@ -290,9 +290,9 @@ static int tegra_bo_get_pages(struct drm_device *drm, struct tegra_bo *bo)
    goto put_pages;
    }

    - err = dma_map_sg(drm->dev, bo->sgt->sgl, bo->sgt->nents,
    - DMA_FROM_DEVICE);
    - if (err == 0) {
    + bo->sgt->nents = dma_map_sg(drm->dev, bo->sgt->sgl, bo->sgt->orig_nents,
    + DMA_FROM_DEVICE);
    + if (bo->sgt->nents == 0) {
    err = -EFAULT;
    goto free_sgt;
    }
    @@ -571,7 +571,8 @@ int tegra_drm_mmap(struct file *file, struct vm_area_struct *vma)
    goto free;
    }

    - if (dma_map_sg(attach->dev, sgt->sgl, sgt->nents, dir) == 0)
    + sgt->nents = dma_map_sg(attach->dev, sgt->sgl, sgt->orig_nents, dir);
    + if (sgt->nents == 0)
    goto free;

    return sgt;
    @@ -590,7 +591,7 @@ static void tegra_gem_prime_unmap_dma_buf(struct dma_buf_attachment *attach,
    struct tegra_bo *bo = to_tegra_bo(gem);

    if (bo->pages)
    - 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);
    @@ -609,7 +610,7 @@ static int tegra_gem_prime_begin_cpu_access(struct dma_buf *buf,
    struct drm_device *drm = gem->dev;

    if (bo->pages)
    - dma_sync_sg_for_cpu(drm->dev, bo->sgt->sgl, bo->sgt->nents,
    + dma_sync_sg_for_cpu(drm->dev, bo->sgt->sgl, bo->sgt->orig_nents,
    DMA_FROM_DEVICE);

    return 0;
    @@ -623,8 +624,8 @@ static int tegra_gem_prime_end_cpu_access(struct dma_buf *buf,
    struct drm_device *drm = gem->dev;

    if (bo->pages)
    - dma_sync_sg_for_device(drm->dev, bo->sgt->sgl, bo->sgt->nents,
    - DMA_TO_DEVICE);
    + dma_sync_sg_for_device(drm->dev, bo->sgt->sgl,
    + bo->sgt->orig_nents, DMA_TO_DEVICE);

    return 0;
    }
    diff --git a/drivers/gpu/drm/tegra/plane.c b/drivers/gpu/drm/tegra/plane.c
    index 9ccfb56..3982bf8 100644
    --- a/drivers/gpu/drm/tegra/plane.c
    +++ b/drivers/gpu/drm/tegra/plane.c
    @@ -130,9 +130,10 @@ static int tegra_dc_pin(struct tegra_dc *dc, struct tegra_plane_state *state)
    }

    if (sgt) {
    - err = dma_map_sg(dc->dev, sgt->sgl, sgt->nents,
    - DMA_TO_DEVICE);
    - if (err == 0) {
    + sgt->nents = dma_map_sg(dc->dev, sgt->sgl,
    + sgt->orig_nents,
    + DMA_TO_DEVICE);
    + if (sgt->nents == 0) {
    err = -ENOMEM;
    goto unpin;
    }
    @@ -143,7 +144,7 @@ static int tegra_dc_pin(struct tegra_dc *dc, struct tegra_plane_state *state)
    * map its SG table to a single contiguous chunk of
    * I/O virtual memory.
    */
    - if (err > 1) {
    + if (sgt->nents > 1) {
    err = -EINVAL;
    goto unpin;
    }
    @@ -165,7 +166,7 @@ static int tegra_dc_pin(struct tegra_dc *dc, struct tegra_plane_state *state)
    struct sg_table *sgt = state->sgt[i];

    if (sgt)
    - dma_unmap_sg(dc->dev, sgt->sgl, sgt->nents,
    + dma_unmap_sg(dc->dev, sgt->sgl, sgt->orig_nents,
    DMA_TO_DEVICE);

    host1x_bo_unpin(dc->dev, &bo->base, sgt);
    @@ -185,7 +186,7 @@ static void tegra_dc_unpin(struct tegra_dc *dc, struct tegra_plane_state *state)
    struct sg_table *sgt = state->sgt[i];

    if (sgt)
    - dma_unmap_sg(dc->dev, sgt->sgl, sgt->nents,
    + dma_unmap_sg(dc->dev, sgt->sgl, sgt->orig_nents,
    DMA_TO_DEVICE);

    host1x_bo_unpin(dc->dev, &bo->base, sgt);
    --
    1.9.1
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