[PATCH] dma-direct: Restore arch_dma_alloc() for the DMA_ATTR_NO_KERNEL_MAPPING case
flat view
COOLING6d
IN LINUX-NEXT
From: Marek Szyprowski <m.szyprowski@samsung.com>
Date: 2026-09-30 13:58:18
Also in:
linux-iommu, lkml
Subsystem:
dma mapping helpers, the rest · Maintainers:
Marek Szyprowski, Linus Torvalds
Queued in linux-next as 5e3bc6b44c88 on 2026-10-09.
Commit 849facea92fa ("dma-direct: simplify the DMA_ATTR_NO_KERNEL_MAPPING
handling") moved the DMA_ATTR_NO_KERNEL_MAPPING shortcut in
dma_direct_alloc() in front of the arch_dma_alloc() call. Architectures
providing their own DMA coherent allocator (CONFIG_ARCH_HAS_DMA_ALLOC)
therefore no longer see such requests. ARM 32bit is one of such. Lack of
the call to arch_dma_alloc() results in the lack of proper cache
management on HighMem pages.
Take the dma-direct shortcut only for coherent devices or when the
architecture doesn't provide arch_dma_alloc(). While touching this,
move that check into separate function to avoid duplication in alloc
and free paths.
Fixes: 849facea92fa ("dma-direct: simplify the DMA_ATTR_NO_KERNEL_MAPPING handling")
Reported-by: Aneesh Kumar K.V <aneesh.kumar@kernel.org>
Closes: https://lore.kernel.org/all/yq5ams2akznl.fsf@kernel.org/ (local)
Assisted-by: Claude Opus 5.5 [off-list ref]
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
---
kernel/dma/direct.c | 22 ++++++++++++++++++----
1 file changed, 18 insertions(+), 4 deletions(-)
diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index da665ca22d5c..a31bd3129f3f 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c@@ -179,6 +179,22 @@ static struct page *dma_direct_alloc_from_pool(struct device *dev, size_t size, return page; } +/* + * Check if the allocation can skip the kernel mapping and return the page + * pointer as the cookie. + */ +static bool dma_direct_use_no_mapping(struct device *dev, unsigned long attrs) +{ + if ((attrs & (DMA_ATTR_NO_KERNEL_MAPPING | __DMA_ATTR_ALLOC_CC_SHARED)) != + DMA_ATTR_NO_KERNEL_MAPPING) + return false; + if (is_swiotlb_for_alloc(dev)) + return false; + if (IS_ENABLED(CONFIG_ARCH_HAS_DMA_ALLOC) && !dev_is_dma_coherent(dev)) + return false; + return true; +} + static void *dma_direct_alloc_no_mapping(struct device *dev, size_t size, dma_addr_t *dma_handle, gfp_t gfp) {
@@ -226,8 +242,7 @@ void *dma_direct_alloc(struct device *dev, size_t size, if (attrs & DMA_ATTR_NO_WARN) gfp |= __GFP_NOWARN; - if (((attrs & (DMA_ATTR_NO_KERNEL_MAPPING | __DMA_ATTR_ALLOC_CC_SHARED)) == - DMA_ATTR_NO_KERNEL_MAPPING) && !is_swiotlb_for_alloc(dev)) + if (dma_direct_use_no_mapping(dev, attrs)) return dma_direct_alloc_no_mapping(dev, size, dma_handle, gfp); if (!dev_is_dma_coherent(dev)) {
@@ -374,8 +389,7 @@ void dma_direct_free(struct device *dev, size_t size, if (attrs & __DMA_ATTR_ALLOC_CC_SHARED) mark_mem_encrypted = true; - if (((attrs & (DMA_ATTR_NO_KERNEL_MAPPING | __DMA_ATTR_ALLOC_CC_SHARED)) == - DMA_ATTR_NO_KERNEL_MAPPING) && !is_swiotlb_for_alloc(dev)) { + if (dma_direct_use_no_mapping(dev, attrs)) { /* cpu_addr is a struct page cookie, not a kernel address */ dma_free_contiguous(dev, cpu_addr, size); return;
--
2.43.0