Re: [PATCH] s390/pci: Fix dev.dma_range_map missing sentinel element

[Niklas Schnelle <schnelle@linux.ibm.com>]

On Thu, 2025-03-06 at 16:25 +0100, Niklas Schnelle wrote:
> The fixed commit sets up dev.dma_range_map but missed that this is
> supposed to be an array of struct bus_dma_region with a sentinel element
> with the size field set to 0 at the end. This would lead to overruns in
> e.g. dma_range_map_min(). It could also result in wrong translations
> instead of DMA_MAPPIN_ERROR in translate_phys_to_dma() if the paddr were
> to not fit in the aperture. Fix this by using the dma_direct_set_offset()
> helper which creates a sentinel for us.
> 
> Fixes: d236843a6964 ("s390/pci: store DMA offset in bus_dma_region")
> Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
> ---
> This is based on iommu/next which contains the fixed commit
> ---
>  arch/s390/pci/pci_bus.c | 24 +++++++++++-------------
>  1 file changed, 11 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/s390/pci/pci_bus.c b/arch/s390/pci/pci_bus.c
> index 0e725039861f92925a38f7ff7cb6de6b0d965ac3..14310c3b48860a16de13536adf95ef99e6af21cc 100644
> --- a/arch/s390/pci/pci_bus.c
> +++ b/arch/s390/pci/pci_bus.c
> @@ -287,23 +287,21 @@ static struct zpci_bus *zpci_bus_alloc(int topo, bool topo_is_tid)
>  static void pci_dma_range_setup(struct pci_dev *pdev)
>  {
>  	struct zpci_dev *zdev = to_zpci(pdev);
> -	struct bus_dma_region *map;
> -	u64 aligned_end;
> +	u64 aligned_end, size;
> +	dma_addr_t dma_start;
> +	int ret;
>  
> -	map = kzalloc(sizeof(*map), GFP_KERNEL);
> -	if (!map)
> -		return;
> -
> -	map->cpu_start = 0;
> -	map->dma_start = PAGE_ALIGN(zdev->start_dma);
> +	dma_start = PAGE_ALIGN(zdev->start_dma);
>  	aligned_end = PAGE_ALIGN_DOWN(zdev->end_dma + 1);
> -	if (aligned_end >= map->dma_start)
> -		map->size = aligned_end - map->dma_start;
> +	if (aligned_end >= dma_start)
> +		size = aligned_end - dma_start;
>  	else
> -		map->size = 0;
> -	WARN_ON_ONCE(map->size == 0);
> +		size = 0;
> +	WARN_ON_ONCE(size == 0);
>  
> -	pdev->dev.dma_range_map = map;
> +	ret = dma_direct_set_offset(&pdev->dev, 0, dma_start, size);
> +	if (ret)
> +		pr_err("Failed to allocate DMA range map for %s\n", pci_name(pdev));

Arguably one might want to use dev_err() here but the rest of the file
uses pr_err(). On the other hand dma_direct_set_offset() uses dev_err()
in case there is already a dev.dma_range_map.

Also maybe s/allocate/set up/ since we're not checking just for -ENOMEM

>  }
>  
>  void pcibios_bus_add_device(struct pci_dev *pdev)
> 
> ---
> base-commit: e840414e5a73ac02ffba6299b46f535a0b7cba98
> change-id: 20250306-fix_dma_map_alloc-b3b05903dcfb
> 
> Best regards,