[bug report] iommu: Implement common IOMMU ops for DMA mapping

Robin Murphy

2016-11-15 11:43:40 UTC

Hi Dan,

Post by Dan Carpenter
Hello Robin Murphy,
The patch 0db2e5d18f76: "iommu: Implement common IOMMU ops for DMA
mapping" from Oct 1, 2015, leads to the following static checker
drivers/iommu/dma-iommu.c:377 iommu_dma_alloc()
warn: use 'gfp' here instead of GFP_XXX?
drivers/iommu/dma-iommu.c
343 struct page **iommu_dma_alloc(struct device *dev, size_t size, gfp_t gfp,
^^^^^^^^^
344 unsigned long attrs, int prot, dma_addr_t *handle,
345 void (*flush_page)(struct device *, const void *, phys_addr_t))
346 {
347 struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
348 struct iova_domain *iovad = cookie_iovad(domain);
349 struct iova *iova;
350 struct page **pages;
351 struct sg_table sgt;
352 dma_addr_t dma_addr;
353 unsigned int count, min_size, alloc_sizes = domain->pgsize_bitmap;
354
355 *handle = DMA_ERROR_CODE;
356
357 min_size = alloc_sizes & -alloc_sizes;
358 if (min_size < PAGE_SIZE) {
359 min_size = PAGE_SIZE;
360 alloc_sizes |= PAGE_SIZE;
361 } else {
362 size = ALIGN(size, min_size);
363 }
364 if (attrs & DMA_ATTR_ALLOC_SINGLE_PAGES)
365 alloc_sizes = min_size;
366
367 count = PAGE_ALIGN(size) >> PAGE_SHIFT;
368 pages = __iommu_dma_alloc_pages(count, alloc_sizes >> PAGE_SHIFT, gfp);
^^^^
Here we use gfp.
369 if (!pages)
370 return NULL;
371
372 iova = __alloc_iova(domain, size, dev->coherent_dma_mask);
373 if (!iova)
374 goto out_free_pages;
375
376 size = iova_align(iovad, size);
377 if (sg_alloc_table_from_pages(&sgt, pages, count, 0, size, GFP_KERNEL))
^^^^^^^^^^
Here we're using GFP_KERNEL. I don't know the code well enough to say
if it was intentional.

Yes, it's intentional - the SG table is a separate (transient) thing to
help map the buffer itself, and iommu_dma_alloc() should only be called
from blocking-safe contexts anyway (since __iommu_dma_alloc_pages() may
need to vmalloc() a large array to keep track of the pages if the buffer
being allocated is massive - the GFP_KERNEL in the other case there is
deliberate, too).

Thanks,
Robin.

Post by Dan Carpenter
378 goto out_free_iova;
379
380 if (!(prot & IOMMU_CACHE)) {
381 struct sg_mapping_iter miter;
382 /*
383 * The CPU-centric flushing implied by SG_MITER_TO_SG isn't
384 * sufficient here, so skip it by using the "wrong" direction.
385 */
386 sg_miter_start(&miter, sgt.sgl, sgt.orig_nents, SG_MITER_FROM_SG);
regards,
dan carpenter