linux-kernel - Re: [PATCH 6/8] dma-mapping: fail early if physical address is mapped through platform callback

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Message-ID: <02240cf7-c4d4-4296-9b1e-87b4231874a1@arm.com>
Date: Fri, 25 Jul 2025 21:04:50 +0100
From: Robin Murphy <robin.murphy@....com>
To: Leon Romanovsky <leon@...nel.org>,
 Marek Szyprowski <m.szyprowski@...sung.com>
Cc: Leon Romanovsky <leonro@...dia.com>, Christoph Hellwig <hch@....de>,
 Jonathan Corbet <corbet@....net>, Madhavan Srinivasan <maddy@...ux.ibm.com>,
 Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
 "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Eugenio Pérez
 <eperezma@...hat.com>, Alexander Potapenko <glider@...gle.com>,
 Marco Elver <elver@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>,
 Masami Hiramatsu <mhiramat@...nel.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Jérôme Glisse <jglisse@...hat.com>,
 Andrew Morton <akpm@...ux-foundation.org>, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
 iommu@...ts.linux.dev, virtualization@...ts.linux.dev,
 kasan-dev@...glegroups.com, linux-trace-kernel@...r.kernel.org,
 linux-mm@...ck.org
Subject: Re: [PATCH 6/8] dma-mapping: fail early if physical address is mapped
 through platform callback

On 2025-06-25 2:19 pm, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@...dia.com>
> 
> All platforms which implement map_page interface don't support physical
> addresses without real struct page. Add condition to check it.

As-is, the condition also needs to cover iommu-dma, because that also 
still doesn't support non-page-backed addresses. You can't just do a 
simple s/page/phys/ rename and hope it's OK because you happen to get 
away with it for coherent, 64-bit, trusted devices.

Thanks,
Robin.

> Signed-off-by: Leon Romanovsky <leonro@...dia.com>
> ---
>   kernel/dma/mapping.c | 15 ++++++++++++++-
>   1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
> index 709405d46b2b..74efb6909103 100644
> --- a/kernel/dma/mapping.c
> +++ b/kernel/dma/mapping.c
> @@ -158,6 +158,7 @@ dma_addr_t dma_map_page_attrs(struct device *dev, struct page *page,
>   {
>   	const struct dma_map_ops *ops = get_dma_ops(dev);
>   	phys_addr_t phys = page_to_phys(page) + offset;
> +	bool is_pfn_valid = true;
>   	dma_addr_t addr;
>   
>   	BUG_ON(!valid_dma_direction(dir));
> @@ -170,8 +171,20 @@ dma_addr_t dma_map_page_attrs(struct device *dev, struct page *page,
>   		addr = dma_direct_map_phys(dev, phys, size, dir, attrs);
>   	else if (use_dma_iommu(dev))
>   		addr = iommu_dma_map_phys(dev, phys, size, dir, attrs);
> -	else
> +	else {
> +		if (IS_ENABLED(CONFIG_DMA_API_DEBUG))
> +			is_pfn_valid = pfn_valid(PHYS_PFN(phys));
> +
> +		if (unlikely(!is_pfn_valid))
> +			return DMA_MAPPING_ERROR;
> +
> +		/*
> +		 * All platforms which implement .map_page() don't support
> +		 * non-struct page backed addresses.
> +		 */
>   		addr = ops->map_page(dev, page, offset, size, dir, attrs);
> +	}
> +
>   	kmsan_handle_dma(phys, size, dir);
>   	trace_dma_map_phys(dev, phys, addr, size, dir, attrs);
>   	debug_dma_map_phys(dev, phys, size, dir, addr, attrs);