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    Subject[PATCH v4 07/38] drm: amdgpu: fix common struct sg_table related issues
    Date
    The Documentation/DMA-API-HOWTO.txt states that the dma_map_sg() function
    returns the number of the created entries in the DMA address space.
    However the subsequent calls to the dma_sync_sg_for_{device,cpu}() and
    dma_unmap_sg must be called with the original number of the entries
    passed to the dma_map_sg().

    struct sg_table is a common structure used for describing a non-contiguous
    memory buffer, used commonly in the DRM and graphics subsystems. It
    consists of a scatterlist with memory pages and DMA addresses (sgl entry),
    as well as the number of scatterlist entries: CPU pages (orig_nents entry)
    and DMA mapped pages (nents entry).

    It turned out that it was a common mistake to misuse nents and orig_nents
    entries, calling DMA-mapping functions with a wrong number of entries or
    ignoring the number of mapped entries returned by the dma_map_sg()
    function.

    To avoid such issues, lets use a common dma-mapping wrappers operating
    directly on the struct sg_table objects and use scatterlist page
    iterators where possible. This, almost always, hides references to the
    nents and orig_nents entries, making the code robust, easier to follow
    and copy/paste safe.

    Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
    Reviewed-by: Christian König <christian.koenig@amd.com>
    ---
    For more information, see '[PATCH v4 00/38] DRM: fix struct sg_table nents
    vs. orig_nents misuse' thread:
    https://lore.kernel.org/dri-devel/20200512085710.14688-1-m.szyprowski@samsung.com/T/
    ---
    drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c | 6 +++---
    drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 9 +++------
    drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c | 8 ++++----
    3 files changed, 10 insertions(+), 13 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..519ce44 100644
    --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
    +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
    @@ -307,8 +307,8 @@ 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))
    + if (dma_map_sgtable(attach->dev, sgt, dir,
    + DMA_ATTR_SKIP_CPU_SYNC))
    goto error_free;
    break;

    @@ -349,7 +349,7 @@ 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_sgtable(attach->dev, sgt, dir, 0);
    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 9cbecd5..57a5d56 100644
    --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
    +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
    @@ -1024,7 +1024,6 @@ 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);
    @@ -1039,9 +1038,8 @@ static int amdgpu_ttm_tt_pin_userptr(struct ttm_tt *ttm)
    goto release_sg;

    /* Map SG to device */
    - r = -ENOMEM;
    - nents = dma_map_sg(adev->dev, ttm->sg->sgl, ttm->sg->nents, direction);
    - if (nents == 0)
    + r = dma_map_sgtable(adev->dev, ttm->sg, direction, 0);
    + if (r)
    goto release_sg;

    /* convert SG to linear array of pages and dma addresses */
    @@ -1072,8 +1070,7 @@ 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_sgtable(adev->dev, ttm->sg, direction, 0);
    sg_free_table(ttm->sg);

    #if IS_ENABLED(CONFIG_DRM_AMDGPU_USERPTR)
    diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
    index d399e58..75495a7 100644
    --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
    +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
    @@ -477,11 +477,11 @@ int amdgpu_vram_mgr_alloc_sgt(struct amdgpu_device *adev,
    if (r)
    goto error_free;

    - for_each_sg((*sgt)->sgl, sg, num_entries, i)
    + for_each_sgtable_sg(*sgt, sg, i)
    sg->length = 0;

    node = mem->mm_node;
    - for_each_sg((*sgt)->sgl, sg, num_entries, i) {
    + for_each_sgtable_sg(*sgt, sg, i) {
    phys_addr_t phys = (node->start << PAGE_SHIFT) +
    adev->gmc.aper_base;
    size_t size = node->size << PAGE_SHIFT;
    @@ -501,7 +501,7 @@ int amdgpu_vram_mgr_alloc_sgt(struct amdgpu_device *adev,
    return 0;

    error_unmap:
    - for_each_sg((*sgt)->sgl, sg, num_entries, i) {
    + for_each_sgtable_sg(*sgt, sg, i) {
    if (!sg->length)
    continue;

    @@ -532,7 +532,7 @@ void amdgpu_vram_mgr_free_sgt(struct amdgpu_device *adev,
    struct scatterlist *sg;
    int i;

    - for_each_sg(sgt->sgl, sg, sgt->nents, i)
    + for_each_sgtable_sg(sgt, sg, i)
    dma_unmap_resource(dev, sg->dma_address,
    sg->length, dir,
    DMA_ATTR_SKIP_CPU_SYNC);
    --
    1.9.1
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