Re: [PATCH] sparc: iommu/pci_sun4v: fix page alignment in dma mapping

Hi Stian,

On Tue, 2026-02-17 at 16:03 +0100, [email protected] wrote:
> From: Stian Halseth <[email protected]>
> 
> '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.
> 
> Fixes: 38c0d0ebf520 ("sparc: Use physical address DMA mapping")
> 
> Reported-by: Stian Halseth <[email protected]>
> Suggested-by: Marek Szyprowski <[email protected]>
> Signed-off-by: Stian Halseth <[email protected]>
> ---
>  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);
> +
>  	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;
>  	}

Thanks a lot for your patch! Please follow this guide [1] to send your patch in
a new thread and also making sure you are sending it to the right recipients.

Adrian

> [1] https://nickdesaulniers.github.io/blog/2017/05/16/submitting-your-first-patch-to-the-linux-kernel-and-responding-to-feedback/

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer
`. `'   Physicist
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