Re: [PATCH v2] sparc: Fix page alignment in dma mapping

[Marek Szyprowski]

On 17.02.2026 18:10, stian@xxxxxx wrote:
> From: Stian Halseth <stian@xxxxxx>
>
> 'phys' may include an offset within the page, while 'base_paddr' is already
> page-aligned. This caused incorrect DMA mapping in dma_4u_map_phys and
> dma_4v_map_phys.
>
> Fix both functions by masking phys with IO_PAGE_MASK or subtracting the
> page offset, covering both generic SPARC code and sun4v.
>
> Fixes: 38c0d0ebf520 ("sparc: Use physical address DMA mapping")
> Reported-by: Stian Halseth <stian@xxxxxx>
> Closes: https://protect2.fireeye.com/v1/url?k=4d8fbc00-1214850c-4d8e374f-000babff3563-ee1be24be576e072&q=1&e=0f8967ce-f558-4339-bddb-f324ec46c035&u=https%3A%2F%2Fgithub.com%2Fsparclinux%2Fissues%2Fissues%2F75
> Suggested-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> Signed-off-by: Stian Halseth <stian@xxxxxx>
> ---
>   arch/sparc/kernel/iommu.c     | 2 ++
>   arch/sparc/kernel/pci_sun4v.c | 2 +-
>   2 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/sparc/kernel/iommu.c b/arch/sparc/kernel/iommu.c
> index 46ef88bc9c26..f3755a388ac7 100644
> --- a/arch/sparc/kernel/iommu.c
> +++ b/arch/sparc/kernel/iommu.c
> @@ -312,6 +312,8 @@ static dma_addr_t dma_4u_map_phys(struct device *dev, phys_addr_t phys,
>   	if (direction != DMA_TO_DEVICE)
>   		iopte_protection |= IOPTE_WRITE;
>   
> +	phys -= offset_in_page(phys);
> +

I've just noticed that IO_PAGE_SIZE might not equal to PAGE_SIZE (not 
sure if this is true in case of SPARCs), so it would be better to rely 
on IO_PAGE_MASK or IO_PAGE_SIZE only. Just unify the fix for the both 
affected functions either by masking phys with IO_PAGE_SIZE where it is 
used or by subtracting (phys & ~IO_PAGE_MASK) from it.

>   	for (i = 0; i < npages; i++, base++, phys += IO_PAGE_SIZE)
>   		iopte_val(*base) = iopte_protection | phys;
>   
> diff --git a/arch/sparc/kernel/pci_sun4v.c b/arch/sparc/kernel/pci_sun4v.c
> index 791f0a76665f..2f30eeac4861 100644
> --- a/arch/sparc/kernel/pci_sun4v.c
> +++ b/arch/sparc/kernel/pci_sun4v.c
> @@ -411,7 +411,7 @@ static dma_addr_t dma_4v_map_phys(struct device *dev, phys_addr_t phys,
>   	iommu_batch_start(dev, prot, entry);
>   
>   	for (i = 0; i < npages; i++, phys += IO_PAGE_SIZE) {
> -		long err = iommu_batch_add(phys, mask);
> +		long err = iommu_batch_add(phys & IO_PAGE_MASK, mask);
>   		if (unlikely(err < 0L))
>   			goto iommu_map_fail;
>   	}

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland