linux-kernel - Re: [PATCH] dma-mapping: fix missing clear bdr in check_ram_in_range

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Message-ID: <6f6e2eaa-9f56-4400-a555-7264d4596233@samsung.com>
Date: Wed, 12 Mar 2025 13:48:16 +0100
From: Marek Szyprowski <m.szyprowski@...sung.com>
To: Baochen Qiang <quic_bqiang@...cinc.com>, robin.murphy@....com,
	justin.he@....com, hch@....de
Cc: iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dma-mapping: fix missing clear bdr in
 check_ram_in_range_map()

On 07.03.2025 04:03, Baochen Qiang wrote:
> As discussed in [1], if 'bdr' is set once, it would never get
> cleared, hence 0 is always returned.
>
> Refactor the range check hunk into a new helper dma_find_range(),
> which allows 'bdr' to be cleared in each iteration.
>
> Link: https://lore.kernel.org/all/64931fac-085b-4ff3-9314-84bac2fa9bdb@quicinc.com/ # [1]
> Fixes: a409d9600959 ("dma-mapping: fix dma_addressing_limited() if dma_range_map can't cover all system RAM")
> Suggested-by: Christoph Hellwig <hch@....de>
> Signed-off-by: Baochen Qiang <quic_bqiang@...cinc.com>

Thanks, applied to dma-mapping-fixes branch.

> ---
>   kernel/dma/direct.c | 28 ++++++++++++++++++----------
>   1 file changed, 18 insertions(+), 10 deletions(-)
>
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index 5b4e6d3bf7bc..b8fe0b3d0ffb 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -584,6 +584,22 @@ int dma_direct_supported(struct device *dev, u64 mask)
>   	return mask >= phys_to_dma_unencrypted(dev, min_mask);
>   }
>   
> +static const struct bus_dma_region *dma_find_range(struct device *dev,
> +						   unsigned long start_pfn)
> +{
> +	const struct bus_dma_region *m;
> +
> +	for (m = dev->dma_range_map; PFN_DOWN(m->size); m++) {
> +		unsigned long cpu_start_pfn = PFN_DOWN(m->cpu_start);
> +
> +		if (start_pfn >= cpu_start_pfn &&
> +		    start_pfn - cpu_start_pfn < PFN_DOWN(m->size))
> +			return m;
> +	}
> +
> +	return NULL;
> +}
> +
>   /*
>    * To check whether all ram resource ranges are covered by dma range map
>    * Returns 0 when further check is needed
> @@ -593,20 +609,12 @@ static int check_ram_in_range_map(unsigned long start_pfn,
>   				  unsigned long nr_pages, void *data)
>   {
>   	unsigned long end_pfn = start_pfn + nr_pages;
> -	const struct bus_dma_region *bdr = NULL;
> -	const struct bus_dma_region *m;
>   	struct device *dev = data;
>   
>   	while (start_pfn < end_pfn) {
> -		for (m = dev->dma_range_map; PFN_DOWN(m->size); m++) {
> -			unsigned long cpu_start_pfn = PFN_DOWN(m->cpu_start);
> +		const struct bus_dma_region *bdr;
>   
> -			if (start_pfn >= cpu_start_pfn &&
> -			    start_pfn - cpu_start_pfn < PFN_DOWN(m->size)) {
> -				bdr = m;
> -				break;
> -			}
> -		}
> +		bdr = dma_find_range(dev, start_pfn);
>   		if (!bdr)
>   			return 1;
>   
>
> base-commit: 7eb172143d5508b4da468ed59ee857c6e5e01da6

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