dma-mapping: reject __GFP_COMP in dma_alloc_attrs

Bugzilla: https://bugzilla.redhat.com/2181354
Upstream Status: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

commit ffcb754
Author: Christoph Hellwig <hch@lst.de>
Date:   Wed Nov 9 08:37:17 2022 +0100

    dma-mapping: reject __GFP_COMP in dma_alloc_attrs

    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>
    Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>

(cherry picked from commit ffcb754)
Signed-off-by: Jerry Snitselaar <jsnitsel@redhat.com>

Author: snits

arch/arm/mm/dma-mapping.c

@@ -695,14 +695,6 @@ 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;
@@ -1434,15 +1426,6 @@ 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;

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;

kernel/dma/mapping.c

@@ -494,6 +494,14 @@ 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;
+
 	if (dma_alloc_from_dev_coherent(dev, size, dma_handle, &cpu_addr))
 		return cpu_addr;