On Sun, Nov 13, 2022 at 05:35:35PM +0100, Christoph Hellwig wrote:
DMA allocations can never be turned back into a page pointer, so requesting compound pages doesn't make sense and it can't even be supported at all by various backends.
Reject __GFP_COMP with a warning in dma_alloc_attrs, and stop clearing the flag in the arm dma ops and dma-iommu.
Signed-off-by: Christoph Hellwig hch@lst.de
arch/arm/mm/dma-mapping.c | 17 ----------------- drivers/iommu/dma-iommu.c | 3 --- kernel/dma/mapping.c | 8 ++++++++ 3 files changed, 8 insertions(+), 20 deletions(-)
diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c index d7909091cf977..c135f6e37a00c 100644 --- a/arch/arm/mm/dma-mapping.c +++ b/arch/arm/mm/dma-mapping.c @@ -564,14 +564,6 @@ static void *__dma_alloc(struct device *dev, size_t size, dma_addr_t *handle, if (mask < 0xffffffffULL) gfp |= GFP_DMA;
/*
* Following is a work-around (a.k.a. hack) to prevent pages* with __GFP_COMP being passed to split_page() which cannot* handle them. The real problem is that this flag probably* should be 0 on ARM as it is not supported on this* platform; see CONFIG_HUGETLBFS.*/gfp &= ~(__GFP_COMP); args.gfp = gfp;
*handle = DMA_MAPPING_ERROR;
@@ -1093,15 +1085,6 @@ static void *arm_iommu_alloc_attrs(struct device *dev, size_t size, return __iommu_alloc_simple(dev, size, gfp, handle, coherent_flag, attrs);
- /*
* Following is a work-around (a.k.a. hack) to prevent pages* with __GFP_COMP being passed to split_page() which cannot* handle them. The real problem is that this flag probably* should be 0 on ARM as it is not supported on this* platform; see CONFIG_HUGETLBFS.*/- gfp &= ~(__GFP_COMP);
- pages = __iommu_alloc_buffer(dev, size, gfp, attrs, coherent_flag); if (!pages) return NULL;
diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c index 9297b741f5e80..f798c44e09033 100644 --- a/drivers/iommu/dma-iommu.c +++ b/drivers/iommu/dma-iommu.c @@ -744,9 +744,6 @@ static struct page **__iommu_dma_alloc_pages(struct device *dev, /* IOMMU can map any pages, so himem can also be used here */ gfp |= __GFP_NOWARN | __GFP_HIGHMEM;
- /* It makes no sense to muck about with huge pages */
- gfp &= ~__GFP_COMP;
- while (count) { struct page *page = NULL; unsigned int order_size;
diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c index 33437d6206445..c026a5a5e0466 100644 --- a/kernel/dma/mapping.c +++ b/kernel/dma/mapping.c @@ -498,6 +498,14 @@ void *dma_alloc_attrs(struct device *dev, size_t size, dma_addr_t *dma_handle,
WARN_ON_ONCE(!dev->coherent_dma_mask);
- /*
* DMA allocations can never be turned back into a page pointer, so* requesting compound pages doesn't make sense (and can't even be* supported at all by various backends).*/- if (WARN_ON_ONCE(flag & __GFP_COMP))
return NULL;
In RDMA patches, you wrote that GFP_USER is not legal flag either. So it is better to WARN here for everything that is not allowed.
- if (dma_alloc_from_dev_coherent(dev, size, dma_handle, &cpu_addr)) return cpu_addr;
-- 2.30.2