Re: [PATCH v2] iommu/dma: simplify dma_iova_destroy() and drop the free_iova helper

[Marek Szyprowski]

On 03.07.2026 05:37, Honglei Huang wrote:
> dma_iova_destroy() frees the IOVA space through __iommu_dma_iova_unlink()
> using a "free_iova" boolean, which duplicates the IOVA free logic in
> dma_iova_free(). And it frees using the unmapped @mapped_len, which for a
> partially linked reservation is smaller than the reserved size. This
> results in a benign waste as pointed out by Robin, not a leak. So this is
> a cleanup, not a fix.
>
> Drop the duplicated free path. Fold __iommu_dma_iova_unlink into
> dma_iova_unlink and remove the free_iova parameter so it only unmaps.
> dma_iova_destroy then unlinks the mapped range if mapped_len is set and
> unconditionally calls dma_iova_free, which frees the whole reservation
> via dma_iova_size. The freed size now always matches the reserved size,
> and destroy reads as unlink then free.
>
> Note that dma_iova_destroy() no longer routes the free through the flush
> queue; teardown now unmaps synchronously and frees directly, matching
> dma_iova_free().
>
> No functional change intended for callers.
>
> Suggested-by: Leon Romanovsky <leonro@xxxxxxxxxx>
> Signed-off-by: Honglei Huang <honghuan@xxxxxxx>


Applied to dma-mapping-for-next. Thanks!


> ---
> Changes since v1:
>  - Reframed from an IOVA-leak fix into a cleanup; dropped Fixes:/Cc: stable.
>  - Fold the free_iova helper into dma_iova_unlink() according to Leon's
>    diff, so destroy is unlink + dma_iova_free(). Added Suggested-by: Leon.
>
>  drivers/iommu/dma-iommu.c | 57 +++++++++++++++------------------------
>  1 file changed, 22 insertions(+), 35 deletions(-)
>
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index 9abaec0703e..5598ed4bff7 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -2068,10 +2068,20 @@ static void iommu_dma_iova_unlink_range_slow(struct device *dev,
>  		arch_sync_dma_flush();
>  }
>  
> -static void __iommu_dma_iova_unlink(struct device *dev,
> -		struct dma_iova_state *state, size_t offset, size_t size,
> -		enum dma_data_direction dir, unsigned long attrs,
> -		bool free_iova)
> +/**
> + * dma_iova_unlink - Unlink a range of IOVA space
> + * @dev: DMA device
> + * @state: IOVA state
> + * @offset: offset into the IOVA state to unlink
> + * @size: size of the buffer
> + * @dir: DMA direction
> + * @attrs: attributes of mapping properties
> + *
> + * Unlink a range of IOVA space for the given IOVA state.
> + */
> +void dma_iova_unlink(struct device *dev, struct dma_iova_state *state,
> +		size_t offset, size_t size, enum dma_data_direction dir,
> +		unsigned long attrs)
>  {
>  	struct iommu_domain *domain = iommu_get_dma_domain(dev);
>  	struct iommu_dma_cookie *cookie = domain->iova_cookie;
> @@ -2087,35 +2097,13 @@ static void __iommu_dma_iova_unlink(struct device *dev,
>  		iommu_dma_iova_unlink_range_slow(dev, addr, size, dir, attrs);
>  
>  	iommu_iotlb_gather_init(&iotlb_gather);
> -	iotlb_gather.queued = free_iova && READ_ONCE(cookie->fq_domain);
>  
>  	size = iova_align(iovad, size + iova_start_pad);
>  	addr -= iova_start_pad;
>  	unmapped = iommu_unmap_fast(domain, addr, size, &iotlb_gather);
>  	WARN_ON(unmapped != size);
>  
> -	if (!iotlb_gather.queued)
> -		iommu_iotlb_sync(domain, &iotlb_gather);
> -	if (free_iova)
> -		iommu_dma_free_iova(domain, addr, size, &iotlb_gather);
> -}
> -
> -/**
> - * dma_iova_unlink - Unlink a range of IOVA space
> - * @dev: DMA device
> - * @state: IOVA state
> - * @offset: offset into the IOVA state to unlink
> - * @size: size of the buffer
> - * @dir: DMA direction
> - * @attrs: attributes of mapping properties
> - *
> - * Unlink a range of IOVA space for the given IOVA state.
> - */
> -void dma_iova_unlink(struct device *dev, struct dma_iova_state *state,
> -		size_t offset, size_t size, enum dma_data_direction dir,
> -		unsigned long attrs)
> -{
> -	 __iommu_dma_iova_unlink(dev, state, offset, size, dir, attrs, false);
> +	iommu_iotlb_sync(domain, &iotlb_gather);
>  }
>  EXPORT_SYMBOL_GPL(dma_iova_unlink);
>  
> @@ -2136,14 +2124,13 @@ void dma_iova_destroy(struct device *dev, struct dma_iova_state *state,
>  		unsigned long attrs)
>  {
>  	if (mapped_len)
> -		__iommu_dma_iova_unlink(dev, state, 0, mapped_len, dir, attrs,
> -				true);
> -	else
> -		/*
> -		 * We can be here if first call to dma_iova_link() failed and
> -		 * there is nothing to unlink, so let's be more clear.
> -		 */
> -		dma_iova_free(dev, state);
> +		dma_iova_unlink(dev, state, 0, mapped_len, dir, attrs);
> +
> +	/*
> +	 * We can be here if the first call to dma_iova_link() failed and
> +	 * there is nothing to unlink, so let's be more clear.
> +	 */
> +	dma_iova_free(dev, state);
>  }
>  EXPORT_SYMBOL_GPL(dma_iova_destroy);
>  
>
> base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482

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