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    Subject[PATCH 5.9 102/391] xen: gntdev: fix common struct sg_table related issues
    Date
    From: Marek Szyprowski <m.szyprowski@samsung.com>

    [ Upstream commit d1749eb1ab85e04e58c29e58900e3abebbdd6e82 ]

    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>
    Acked-by: Juergen Gross <jgross@suse.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/xen/gntdev-dmabuf.c | 13 ++++++-------
    1 file changed, 6 insertions(+), 7 deletions(-)

    diff --git a/drivers/xen/gntdev-dmabuf.c b/drivers/xen/gntdev-dmabuf.c
    index b1b6eebafd5de..4c13cbc99896a 100644
    --- a/drivers/xen/gntdev-dmabuf.c
    +++ b/drivers/xen/gntdev-dmabuf.c
    @@ -247,10 +247,9 @@ static void dmabuf_exp_ops_detach(struct dma_buf *dma_buf,

    if (sgt) {
    if (gntdev_dmabuf_attach->dir != DMA_NONE)
    - dma_unmap_sg_attrs(attach->dev, sgt->sgl,
    - sgt->nents,
    - gntdev_dmabuf_attach->dir,
    - DMA_ATTR_SKIP_CPU_SYNC);
    + dma_unmap_sgtable(attach->dev, sgt,
    + gntdev_dmabuf_attach->dir,
    + DMA_ATTR_SKIP_CPU_SYNC);
    sg_free_table(sgt);
    }

    @@ -288,8 +287,8 @@ dmabuf_exp_ops_map_dma_buf(struct dma_buf_attachment *attach,
    sgt = dmabuf_pages_to_sgt(gntdev_dmabuf->pages,
    gntdev_dmabuf->nr_pages);
    if (!IS_ERR(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)) {
    sg_free_table(sgt);
    kfree(sgt);
    sgt = ERR_PTR(-ENOMEM);
    @@ -633,7 +632,7 @@ dmabuf_imp_to_refs(struct gntdev_dmabuf_priv *priv, struct device *dev,

    /* Now convert sgt to array of pages and check for page validity. */
    i = 0;
    - for_each_sg_page(sgt->sgl, &sg_iter, sgt->nents, 0) {
    + for_each_sgtable_page(sgt, &sg_iter, 0) {
    struct page *page = sg_page_iter_page(&sg_iter);
    /*
    * Check if page is valid: this can happen if we are given
    --
    2.27.0


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