From 5e3bc6b44c8853bcc7782eac122c5baf2d02f399 Mon Sep 17 00:00:00 2001 From: Marek Szyprowski Date: Wed, 30 Sep 2026 15:57:32 +0200 Subject: [PATCH] dma-direct: Restore arch_dma_alloc() for the DMA_ATTR_NO_KERNEL_MAPPING case 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 Closes: https://lore.kernel.org/all/yq5ams2akznl.fsf@kernel.org/ Assisted-by: Claude Opus 5.5 Link: https://lore.kernel.org/r/20260930135734.1013905-1-m.szyprowski@samsung.com Signed-off-by: Marek Szyprowski --- 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 ea64453d7370..25e9a86835fd 100644 --- a/kernel/dma/direct.c +++ b/kernel/dma/direct.c @@ -181,6 +181,22 @@ 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) { @@ -228,8 +244,7 @@ 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)) { @@ -376,8 +391,7 @@ 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;