[PATCH] dma-mapping: fix missing clear bdr in check_ram_in_range_map()

[PATCH] dma-mapping: fix missing clear bdr in check_ram_in_range_map()

[Baochen Qiang]

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@lst.de>
Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.com>
---
 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
-- 
2.34.1

Re: [PATCH] dma-mapping: fix missing clear bdr in check_ram_in_range_map()

[Marek Szyprowski]

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@lst.de>
> Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.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