The patch titled Subject: dma-debug: don't report false positives with DMA_BOUNCE_UNALIGNED_KMALLOC has been added to the -mm mm-hotfixes-unstable branch. Its filename is dma-debug-dont-report-false-positives-with-dma_bounce_unaligned_kmalloc.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Marek Szyprowski m.szyprowski@samsung.com Subject: dma-debug: don't report false positives with DMA_BOUNCE_UNALIGNED_KMALLOC Date: Thu, 9 Oct 2025 16:15:08 +0200

Commit 370645f41e6e ("dma-mapping: force bouncing if the kmalloc() size is not cache-line-aligned") introduced DMA_BOUNCE_UNALIGNED_KMALLOC feature and lets architecture specific code to configure kmalloc slabs with sizes smaller than the value of dma_get_cache_alignment().

When that feature is enabled, the physical address of some small kmalloc()-ed buffers might be not aligned to the CPU cachelines, thus not really suitable for typical DMA. To properly handle that case a SWIOTLB buffer bouncing is used, so no CPU cache corruption occurs. When that happens, there is no point reporting a false-positive DMA-API warning that the buffer is not properly aligned, as this is not a client driver fault.

Link: https://lkml.kernel.org/r/20251009141508.2342138-1-m.szyprowski@samsung.com Fixes: 370645f41e6e ("dma-mapping: force bouncing if the kmalloc() size is not cache-line-aligned") Signed-off-by: Marek Szyprowski m.szyprowski@samsung.com Cc: Catalin Marinas catalin.marinas@arm.com Cc: Christoph Hellwig hch@lst.de Cc: Inki Dae m.szyprowski@samsung.com Cc: Robin Murohy robin.murphy@arm.com Cc: "Isaac J. Manjarres" isaacmanjarres@google.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

kernel/dma/debug.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/kernel/dma/debug.c~dma-debug-dont-report-false-positives-with-dma_bounce_unaligned_kmalloc +++ a/kernel/dma/debug.c @@ -23,6 +23,7 @@ #include <linux/ctype.h> #include <linux/list.h> #include <linux/slab.h> +#include <linux/swiotlb.h> #include <asm/sections.h> #include "debug.h"

@@ -594,7 +595,9 @@ static void add_dma_entry(struct dma_deb if (rc == -ENOMEM) { pr_err_once("cacheline tracking ENOMEM, dma-debug disabled\n"); global_disable = true; - } else if (rc == -EEXIST && !(attrs & DMA_ATTR_SKIP_CPU_SYNC)) { + } else if (rc == -EEXIST && !(attrs & DMA_ATTR_SKIP_CPU_SYNC) && + !(IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC) && + is_swiotlb_allocated())) { err_printk(entry->dev, entry, "cacheline tracking EEXIST, overlapping mappings aren't supported\n"); } _

Patches currently in -mm which might be from m.szyprowski@samsung.com are

dma-debug-dont-report-false-positives-with-dma_bounce_unaligned_kmalloc.patch