dma-mapping: remove CONFIG_DMA_REMAP

CONFIG_DMA_REMAP is used to build a few helpers around the core
vmalloc code, and to use them in case there is a highmem page in
dma-direct, and to make dma coherent allocations be able to use
non-contiguous pages allocations for DMA allocations in the dma-iommu
layer.

Right now it needs to be explicitly selected by architectures, and
is only done so by architectures that require remapping to deal
with devices that are not DMA coherent. Make it unconditional for
builds with CONFIG_MMU as it is very little extra code, but makes
it much more likely that large DMA allocations succeed on x86.

This fixes hot plugging a NVMe thunderbolt SSD for me, which tries
to allocate a 1MB buffer that is otherwise hard to obtain due to
memory fragmentation on a heavily used laptop.

Signed-off-by: Christoph Hellwig <[e-mail]>
Reviewed-by: Robin Murphy <[e-mail]>

arch/arm/Kconfig

···
 	select DMA_DECLARE_COHERENT
 	select DMA_GLOBAL_POOL if !MMU
 	select DMA_OPS
-	select DMA_REMAP if MMU
+	select DMA_NONCOHERENT_MMAP if MMU
 	select EDAC_SUPPORT
 	select EDAC_ATOMIC_SCRUB
 	select GENERIC_ALLOCATOR

arch/xtensa/Kconfig

···
 	select BUILDTIME_TABLE_SORT
 	select CLONE_BACKWARDS
 	select COMMON_CLK
-	select DMA_REMAP if MMU
+	select DMA_NONCOHERENT_MMAP if MMU
 	select GENERIC_ATOMIC64
 	select GENERIC_IRQ_SHOW
 	select GENERIC_PCI_IOMAP

drivers/iommu/dma-iommu.c

···
 	return NULL;
 }
 
-#ifdef CONFIG_DMA_REMAP
 static struct sg_table *iommu_dma_alloc_noncontiguous(struct device *dev,
 		size_t size, enum dma_data_direction dir, gfp_t gfp,
 		unsigned long attrs)
···
 	sg_free_table(&sh->sgt);
 	kfree(sh);
 }
-#endif /* CONFIG_DMA_REMAP */
 
 static void iommu_dma_sync_single_for_cpu(struct device *dev,
 		dma_addr_t dma_handle, size_t size, enum dma_data_direction dir)
···
 	    dma_free_from_pool(dev, cpu_addr, alloc_size))
 		return;
 
-	if (IS_ENABLED(CONFIG_DMA_REMAP) && is_vmalloc_addr(cpu_addr)) {
+	if (is_vmalloc_addr(cpu_addr)) {
 		/*
 		 * If it the address is remapped, then it's either non-coherent
 		 * or highmem CMA, or an iommu_dma_alloc_remap() construction.
···
 	if (!page)
 		return NULL;
 
-	if (IS_ENABLED(CONFIG_DMA_REMAP) && (!coherent || PageHighMem(page))) {
+	if (!coherent || PageHighMem(page)) {
 		pgprot_t prot = dma_pgprot(dev, PAGE_KERNEL, attrs);
 
 		cpu_addr = dma_common_contiguous_remap(page, alloc_size,
···
 
 	gfp |= __GFP_ZERO;
 
-	if (IS_ENABLED(CONFIG_DMA_REMAP) && gfpflags_allow_blocking(gfp) &&
+	if (gfpflags_allow_blocking(gfp) &&
 	    !(attrs & DMA_ATTR_FORCE_CONTIGUOUS)) {
 		return iommu_dma_alloc_remap(dev, size, handle, gfp,
 				dma_pgprot(dev, PAGE_KERNEL, attrs), attrs);
···
 	if (off >= nr_pages || vma_pages(vma) > nr_pages - off)
 		return -ENXIO;
 
-	if (IS_ENABLED(CONFIG_DMA_REMAP) && is_vmalloc_addr(cpu_addr)) {
+	if (is_vmalloc_addr(cpu_addr)) {
 		struct page **pages = dma_common_find_pages(cpu_addr);
 
 		if (pages)
···
 	struct page *page;
 	int ret;
 
-	if (IS_ENABLED(CONFIG_DMA_REMAP) && is_vmalloc_addr(cpu_addr)) {
+	if (is_vmalloc_addr(cpu_addr)) {
 		struct page **pages = dma_common_find_pages(cpu_addr);
 
 		if (pages) {
···
 	.free			= iommu_dma_free,
 	.alloc_pages		= dma_common_alloc_pages,
 	.free_pages		= dma_common_free_pages,
-#ifdef CONFIG_DMA_REMAP
 	.alloc_noncontiguous	= iommu_dma_alloc_noncontiguous,
 	.free_noncontiguous	= iommu_dma_free_noncontiguous,
-#endif
 	.mmap			= iommu_dma_mmap,
 	.get_sgtable		= iommu_dma_get_sgtable,
 	.map_page		= iommu_dma_map_page,

kernel/dma/Kconfig

···
 	select DMA_DECLARE_COHERENT
 	bool
 
-config DMA_REMAP
-	bool
-	depends on MMU
-	select DMA_NONCOHERENT_MMAP
-
 config DMA_DIRECT_REMAP
 	bool
-	select DMA_REMAP
 	select DMA_COHERENT_POOL
+	select DMA_NONCOHERENT_MMAP
 
 config DMA_CMA
 	bool "DMA Contiguous Memory Allocator"

kernel/dma/Makefile

···
 obj-$(CONFIG_DMA_API_DEBUG)		+= debug.o
 obj-$(CONFIG_SWIOTLB)			+= swiotlb.o
 obj-$(CONFIG_DMA_COHERENT_POOL)		+= pool.o
-obj-$(CONFIG_DMA_REMAP)			+= remap.o
+obj-$(CONFIG_MMU)			+= remap.o
 obj-$(CONFIG_DMA_MAP_BENCHMARK)		+= map_benchmark.o

kernel/dma/direct.c

···
 	page = __dma_direct_alloc_pages(dev, size, gfp & ~__GFP_ZERO);
 	if (!page)
 		return NULL;
+
+	/*
+	 * dma_alloc_contiguous can return highmem pages depending on a
+	 * combination the cma= arguments and per-arch setup.  These need to be
+	 * remapped to return a kernel virtual address.
+	 */
 	if (PageHighMem(page)) {
-		/*
-		 * Depending on the cma= arguments and per-arch setup,
-		 * dma_alloc_contiguous could return highmem pages.
-		 * Without remapping there is no way to return them here, so
-		 * log an error and fail.
-		 */
-		if (!IS_ENABLED(CONFIG_DMA_REMAP)) {
-			dev_info(dev, "Rejecting highmem page from CMA.\n");
-			goto out_free_pages;
-		}
 		remap = true;
 		set_uncached = false;
 	}
···
 	    dma_free_from_pool(dev, cpu_addr, PAGE_ALIGN(size)))
 		return;
 
-	if (IS_ENABLED(CONFIG_DMA_REMAP) && is_vmalloc_addr(cpu_addr)) {
+	if (is_vmalloc_addr(cpu_addr)) {
 		vunmap(cpu_addr);
 	} else {
 		if (IS_ENABLED(CONFIG_ARCH_HAS_DMA_CLEAR_UNCACHED))