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Message-ID: <3d756d9a-38fa-4e50-8999-cc7232dd595e@samsung.com>
Date: Tue, 2 Sep 2025 10:41:27 +0200
From: Marek Szyprowski <m.szyprowski@...sung.com>
To: Baochen Qiang <baochen.qiang@....qualcomm.com>, Robin Murphy
<robin.murphy@....com>, Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc: iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dma-debug: don't enforce dma mapping check on
noncoherent allocations
On 28.08.2025 10:17, Baochen Qiang wrote:
> As discussed in [1], there is no need to enforce dma mapping check on
> noncoherent allocations, a simple test on the returned CPU address is
> good enough.
>
> Add a new pair of debug helpers and use them for noncoherent alloc/free
> to fix this issue.
>
> Fixes: efa70f2fdc84 ("dma-mapping: add a new dma_alloc_pages API")
> Link: https://lore.kernel.org/all/ff6c1fe6-820f-4e58-8395-df06aa91706c@oss.qualcomm.com # 1
> Signed-off-by: Baochen Qiang <baochen.qiang@....qualcomm.com>
Thanks, applied to dma-mapping-fixes branch.
> ---
> kernel/dma/debug.c | 48 +++++++++++++++++++++++++++++++++++++++++++++++-
> kernel/dma/debug.h | 20 ++++++++++++++++++++
> kernel/dma/mapping.c | 4 ++--
> 3 files changed, 69 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
> index e43c6de2bce4e7d3e58f8d9601a7637d8f6da767..b82399437db03116a396c7d1cebd16b2e1af98c3 100644
> --- a/kernel/dma/debug.c
> +++ b/kernel/dma/debug.c
> @@ -39,6 +39,7 @@ enum {
> dma_debug_sg,
> dma_debug_coherent,
> dma_debug_resource,
> + dma_debug_noncoherent,
> };
>
> enum map_err_types {
> @@ -141,6 +142,7 @@ static const char *type2name[] = {
> [dma_debug_sg] = "scatter-gather",
> [dma_debug_coherent] = "coherent",
> [dma_debug_resource] = "resource",
> + [dma_debug_noncoherent] = "noncoherent",
> };
>
> static const char *dir2name[] = {
> @@ -993,7 +995,8 @@ static void check_unmap(struct dma_debug_entry *ref)
> "[mapped as %s] [unmapped as %s]\n",
> ref->dev_addr, ref->size,
> type2name[entry->type], type2name[ref->type]);
> - } else if (entry->type == dma_debug_coherent &&
> + } else if ((entry->type == dma_debug_coherent ||
> + entry->type == dma_debug_noncoherent) &&
> ref->paddr != entry->paddr) {
> err_printk(ref->dev, entry, "device driver frees "
> "DMA memory with different CPU address "
> @@ -1581,6 +1584,49 @@ void debug_dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
> }
> }
>
> +void debug_dma_alloc_pages(struct device *dev, struct page *page,
> + size_t size, int direction,
> + dma_addr_t dma_addr,
> + unsigned long attrs)
> +{
> + struct dma_debug_entry *entry;
> +
> + if (unlikely(dma_debug_disabled()))
> + return;
> +
> + entry = dma_entry_alloc();
> + if (!entry)
> + return;
> +
> + entry->type = dma_debug_noncoherent;
> + entry->dev = dev;
> + entry->paddr = page_to_phys(page);
> + entry->size = size;
> + entry->dev_addr = dma_addr;
> + entry->direction = direction;
> +
> + add_dma_entry(entry, attrs);
> +}
> +
> +void debug_dma_free_pages(struct device *dev, struct page *page,
> + size_t size, int direction,
> + dma_addr_t dma_addr)
> +{
> + struct dma_debug_entry ref = {
> + .type = dma_debug_noncoherent,
> + .dev = dev,
> + .paddr = page_to_phys(page),
> + .dev_addr = dma_addr,
> + .size = size,
> + .direction = direction,
> + };
> +
> + if (unlikely(dma_debug_disabled()))
> + return;
> +
> + check_unmap(&ref);
> +}
> +
> static int __init dma_debug_driver_setup(char *str)
> {
> int i;
> diff --git a/kernel/dma/debug.h b/kernel/dma/debug.h
> index f525197d3cae605aa7e0499eb2ca6f1ae134ec93..48757ca13f31403f58090e1015de828893b8f94f 100644
> --- a/kernel/dma/debug.h
> +++ b/kernel/dma/debug.h
> @@ -54,6 +54,13 @@ extern void debug_dma_sync_sg_for_cpu(struct device *dev,
> extern void debug_dma_sync_sg_for_device(struct device *dev,
> struct scatterlist *sg,
> int nelems, int direction);
> +extern void debug_dma_alloc_pages(struct device *dev, struct page *page,
> + size_t size, int direction,
> + dma_addr_t dma_addr,
> + unsigned long attrs);
> +extern void debug_dma_free_pages(struct device *dev, struct page *page,
> + size_t size, int direction,
> + dma_addr_t dma_addr);
> #else /* CONFIG_DMA_API_DEBUG */
> static inline void debug_dma_map_page(struct device *dev, struct page *page,
> size_t offset, size_t size,
> @@ -126,5 +133,18 @@ static inline void debug_dma_sync_sg_for_device(struct device *dev,
> int nelems, int direction)
> {
> }
> +
> +static inline void debug_dma_alloc_pages(struct device *dev, struct page *page,
> + size_t size, int direction,
> + dma_addr_t dma_addr,
> + unsigned long attrs)
> +{
> +}
> +
> +static inline void debug_dma_free_pages(struct device *dev, struct page *page,
> + size_t size, int direction,
> + dma_addr_t dma_addr)
> +{
> +}
> #endif /* CONFIG_DMA_API_DEBUG */
> #endif /* _KERNEL_DMA_DEBUG_H */
> diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
> index 107e4a4d251df65fb86a1d7302261c31138061b7..56de28a3b1799f7c18f7e3f8e5ecd438c5748677 100644
> --- a/kernel/dma/mapping.c
> +++ b/kernel/dma/mapping.c
> @@ -712,7 +712,7 @@ struct page *dma_alloc_pages(struct device *dev, size_t size,
> if (page) {
> trace_dma_alloc_pages(dev, page_to_virt(page), *dma_handle,
> size, dir, gfp, 0);
> - debug_dma_map_page(dev, page, 0, size, dir, *dma_handle, 0);
> + debug_dma_alloc_pages(dev, page, size, dir, *dma_handle, 0);
> } else {
> trace_dma_alloc_pages(dev, NULL, 0, size, dir, gfp, 0);
> }
> @@ -738,7 +738,7 @@ void dma_free_pages(struct device *dev, size_t size, struct page *page,
> dma_addr_t dma_handle, enum dma_data_direction dir)
> {
> trace_dma_free_pages(dev, page_to_virt(page), dma_handle, size, dir, 0);
> - debug_dma_unmap_page(dev, dma_handle, size, dir);
> + debug_dma_free_pages(dev, page, size, dir, dma_handle);
> __dma_free_pages(dev, size, page, dma_handle, dir);
> }
> EXPORT_SYMBOL_GPL(dma_free_pages);
>
> ---
> base-commit: 95bf875b89b48a95a82aca922eeaf19d52543028
> change-id: 20250828-dma-debug-fix-noncoherent-dma-check-8e6915d58494
>
> Best regards,
Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland
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