Re: [PATCH] arm64/dma-mapping: fix DMA_ATTR_FORCE_CONTIGUOUS mmaping code

[Laura Abbott <labbott-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On 04/21/2017 09:12 AM, Catalin Marinas wrote:
> On Wed, Mar 29, 2017 at 01:55:32PM +0100, Robin Murphy wrote:
>> On 29/03/17 11:05, Andrzej Hajda wrote:
>>> In case of DMA_ATTR_FORCE_CONTIGUOUS allocations vm_area->pages
>>> is invalid. __iommu_mmap_attrs and __iommu_get_sgtable cannot use
>>> it. In first case temporary pages array is passed to iommu_dma_mmap,
>>> in 2nd case single entry sg table is created directly instead
>>> of calling helper.
>>>
>>> Fixes: 44176bb ("arm64: Add support for DMA_ATTR_FORCE_CONTIGUOUS to IOMMU")
>>> Signed-off-by: Andrzej Hajda <a.hajda-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>
>>> ---
>>> Hi,
>>>
>>> I am not familiar with this framework so please don't be too cruel ;)
>>> Alternative solution I see is to always create vm_area->pages,
>>> I do not know which approach is preferred.
>>>
>>> Regards
>>> Andrzej
>>> ---
>>>  arch/arm64/mm/dma-mapping.c | 40 ++++++++++++++++++++++++++++++++++++++--
>>>  1 file changed, 38 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
>>> index f7b5401..bba2bc8 100644
>>> --- a/arch/arm64/mm/dma-mapping.c
>>> +++ b/arch/arm64/mm/dma-mapping.c
>>> @@ -704,7 +704,30 @@ static int __iommu_mmap_attrs(struct device *dev, struct vm_area_struct *vma,
>>>  		return ret;
>>>  
>>>  	area = find_vm_area(cpu_addr);
>>> -	if (WARN_ON(!area || !area->pages))
>>> +	if (WARN_ON(!area))
>>
>> From the look of things, it doesn't seem strictly necessary to change
>> this, but whether that's a good thing is another matter. I'm not sure
>> that dma_common_contiguous_remap() should really be leaving a dangling
>> pointer in area->pages as it apparently does... :/
> 
> On this specific point, I don't think area->pages should be set either
> (cc'ing Laura). As in the vmalloc vs vmap case, area->pages when pages
> need to be freed (via vfree), which is not the case here. The
> dma_common_pages_remap() would need to set area->pages when called
> directly from the iommu DMA ops. Proposal below, not tested with the
> iommu ops. I assume the patch would cause __iommu_mmap_attrs() to return
> -ENXIO if DMA_ATTR_FORCE_CONTIGUOUS is set.
> 
> ------------8<---------------------------------
> diff --git a/drivers/base/dma-mapping.c b/drivers/base/dma-mapping.c
> index efd71cf4fdea..ab7071041141 100644
> --- a/drivers/base/dma-mapping.c
> +++ b/drivers/base/dma-mapping.c
> @@ -277,8 +277,8 @@ EXPORT_SYMBOL(dma_common_mmap);
>   * remaps an array of PAGE_SIZE pages into another vm_area
>   * Cannot be used in non-sleeping contexts
>   */
> -void *dma_common_pages_remap(struct page **pages, size_t size,
> -			unsigned long vm_flags, pgprot_t prot,
> +static struct vm_struct *__dma_common_pages_remap(struct page **pages,
> +			size_t size, unsigned long vm_flags, pgprot_t prot,
>  			const void *caller)
>  {
>  	struct vm_struct *area;
> @@ -287,13 +287,26 @@ void *dma_common_pages_remap(struct page **pages, size_t size,
>  	if (!area)
>  		return NULL;
>  
> -	area->pages = pages;
> -
>  	if (map_vm_area(area, prot, pages)) {
>  		vunmap(area->addr);
>  		return NULL;
>  	}
>  
> +	return area;
> +}
> +
> +void *dma_common_pages_remap(struct page **pages, size_t size,
> +			unsigned long vm_flags, pgprot_t prot,
> +			const void *caller)
> +{
> +	struct vm_struct *area;
> +
> +	area = __dma_common_pages_remap(pages, size, vm_flags, prot, caller);
> +	if (!area)
> +		return NULL;
> +
> +	area->pages = pages;
> +
>  	return area->addr;
>  }
>  
> @@ -308,7 +321,7 @@ void *dma_common_contiguous_remap(struct page *page, size_t size,
>  {
>  	int i;
>  	struct page **pages;
> -	void *ptr;
> +	struct vm_struct *area;
>  	unsigned long pfn;
>  
>  	pages = kmalloc(sizeof(struct page *) << get_order(size), GFP_KERNEL);
> @@ -318,11 +331,13 @@ void *dma_common_contiguous_remap(struct page *page, size_t size,
>  	for (i = 0, pfn = page_to_pfn(page); i < (size >> PAGE_SHIFT); i++)
>  		pages[i] = pfn_to_page(pfn + i);
>  
> -	ptr = dma_common_pages_remap(pages, size, vm_flags, prot, caller);
> +	area = __dma_common_pages_remap(pages, size, vm_flags, prot, caller);
>  
>  	kfree(pages);
>  
> -	return ptr;
> +	if (!area)
> +		return NULL;
> +	return area->addr;
>  }
>  
>  /*
> 

>From a quick glance, this looks okay. I can give a proper tag when
the fix to allow mmaping comes in since I'm guessing -ENXIO is not the
end goal.

Thanks,
Laura