Re: [PATCH v5 13/38] drm: lima: fix common struct sg_table related issues

Looks good for me, patch is: Reviewed-by: Qiang Yu yuq825@gmail.com

Regards, Qiang

On Wed, May 13, 2020 at 9:33 PM Marek Szyprowski m.szyprowski@samsung.com wrote:

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

For more information, see '[PATCH v5 00/38] DRM: fix struct sg_table nents vs. orig_nents misuse' thread: https://lore.kernel.org/linux-iommu/20200513132114.6046-1-m.szyprowski@samsu...

---

drivers/gpu/drm/lima/lima_gem.c | 11 ++++++++--- drivers/gpu/drm/lima/lima_vm.c | 5 ++--- 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/lima/lima_gem.c b/drivers/gpu/drm/lima/lima_gem.c index 5404e0d..cda43f6 100644 --- a/drivers/gpu/drm/lima/lima_gem.c +++ b/drivers/gpu/drm/lima/lima_gem.c @@ -69,8 +69,7 @@ int lima_heap_alloc(struct lima_bo *bo, struct lima_vm *vm) return ret;

    if (bo->base.sgt) {

•           dma_unmap_sg(dev, bo->base.sgt->sgl,
  

•                        bo->base.sgt->nents, DMA_BIDIRECTIONAL);
  

•           dma_unmap_sgtable(dev, bo->base.sgt, DMA_BIDIRECTIONAL, 0);
            sg_free_table(bo->base.sgt);
    } else {
            bo->base.sgt = kmalloc(sizeof(*bo->base.sgt), GFP_KERNEL);
  

@@ -80,7 +79,13 @@ int lima_heap_alloc(struct lima_bo *bo, struct lima_vm *vm) } }

•   dma_map_sg(dev, sgt.sgl, sgt.nents, DMA_BIDIRECTIONAL);
  

•   ret = dma_map_sgtable(dev, &sgt, DMA_BIDIRECTIONAL, 0);
  

•   if (ret) {
  

•           sg_free_table(&sgt);
  

•           kfree(bo->base.sgt);
  

•           bo->base.sgt = NULL;
  

•           return ret;
  

•   }
  
    *bo->base.sgt = sgt;
  
  

diff --git a/drivers/gpu/drm/lima/lima_vm.c b/drivers/gpu/drm/lima/lima_vm.c index 5b92fb8..2b2739a 100644 --- a/drivers/gpu/drm/lima/lima_vm.c +++ b/drivers/gpu/drm/lima/lima_vm.c @@ -124,7 +124,7 @@ int lima_vm_bo_add(struct lima_vm *vm, struct lima_bo *bo, bool create) if (err) goto err_out1;

•   for_each_sg_dma_page(bo->base.sgt->sgl, &sg_iter, bo->base.sgt->nents, 0) {
  

•   for_each_sgtable_dma_page(bo->base.sgt, &sg_iter, 0) {
            err = lima_vm_map_page(vm, sg_page_iter_dma_address(&sg_iter),
                                   bo_va->node.start + offset);
            if (err)
  

@@ -298,8 +298,7 @@ int lima_vm_map_bo(struct lima_vm *vm, struct lima_bo *bo, int pageoff) mutex_lock(&vm->lock);

    base = bo_va->node.start + (pageoff << PAGE_SHIFT);

•   for_each_sg_dma_page(bo->base.sgt->sgl, &sg_iter,
  

•                        bo->base.sgt->nents, pageoff) {
  

•   for_each_sgtable_dma_page(bo->base.sgt, &sg_iter, pageoff) {
            err = lima_vm_map_page(vm, sg_page_iter_dma_address(&sg_iter),
                                   base + offset);
            if (err)
  

-- 1.9.1