Hi Dan,
On 15/11/16 09:44, Dan Carpenter wrote:
> Hello Robin Murphy,
>
> The patch 0db2e5d18f76: "iommu: Implement common IOMMU ops for DMA
> mapping" from Oct 1, 2015, leads to the following static checker
> warning:
>
> 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.
>
> 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
>
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