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 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@samsun... --- 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)