Re: [PATCH v8 01/23] dma-direct: return struct page from dma_direct_alloc_from_pool()

[Leon Romanovsky <leon@kernel.org>]

On Fri, Jul 17, 2026 at 11:34:19PM +0530, Aneesh Kumar K.V (Arm) wrote:
> Commit 5b138c534fda ("dma-direct: factor out a dma_direct_alloc_from_pool
> helper") changed dma_direct_alloc_from_pool() to return the CPU address
> from dma_alloc_from_pool(). That fits dma_direct_alloc(), but
> dma_direct_alloc_pages() also uses the helper and expects a struct page *.
> 
> Fix this by making dma_direct_alloc_from_pool() return the struct page *
> again, and pass the CPU address back through an out-parameter for the
> dma_direct_alloc() caller.
> 
> Fixes: 5b138c534fda ("dma-direct: factor out a dma_direct_alloc_from_pool helper")
> Cc: stable@vger.kernel.org
> Tested-by: Michael Kelley <mhklinux@outlook.com>
> Tested-by: Mostafa Saleh <smostafa@google.com>
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
> ---
>  kernel/dma/direct.c | 18 ++++++++++--------
>  1 file changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index d8219efe3273..363d984d90e7 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -164,22 +164,21 @@ static bool dma_direct_use_pool(struct device *dev, gfp_t gfp)
>  	return !gfpflags_allow_blocking(gfp) && !is_swiotlb_for_alloc(dev);
>  }
>  
> -static void *dma_direct_alloc_from_pool(struct device *dev, size_t size,
> -		dma_addr_t *dma_handle, gfp_t gfp)
> +static struct page *dma_direct_alloc_from_pool(struct device *dev, size_t size,
> +		dma_addr_t *dma_handle, void **cpu_addr, gfp_t gfp)
>  {
>  	struct page *page;
>  	u64 phys_limit;
> -	void *ret;
>  
>  	if (WARN_ON_ONCE(!IS_ENABLED(CONFIG_DMA_COHERENT_POOL)))
>  		return NULL;
>  
>  	gfp |= dma_direct_optimal_gfp_mask(dev, &phys_limit);
> -	page = dma_alloc_from_pool(dev, size, &ret, gfp, dma_coherent_ok);
> +	page = dma_alloc_from_pool(dev, size, cpu_addr, gfp, dma_coherent_ok);
>  	if (!page)
>  		return NULL;
>  	*dma_handle = phys_to_dma_direct(dev, page_to_phys(page));
> -	return ret;
> +	return page;
>  }
>  
>  static void *dma_direct_alloc_no_mapping(struct device *dev, size_t size,
> @@ -247,8 +246,11 @@ void *dma_direct_alloc(struct device *dev, size_t size,
>  	 * the atomic pools instead if we aren't allowed block.
>  	 */
>  	if ((remap || force_dma_unencrypted(dev)) &&
> -	    dma_direct_use_pool(dev, gfp))
> -		return dma_direct_alloc_from_pool(dev, size, dma_handle, gfp);
> +	    dma_direct_use_pool(dev, gfp)) {
> +		page = dma_direct_alloc_from_pool(dev, size, dma_handle,
> +						  &ret, gfp);
> +		return page ? ret : NULL;

Sorry for joining the discussion late, but the line above caught my
attention.

Why do we need both ret and page? We can derive cpu_addr from page and
vice versa. Do we really need the &ret parameter? Or, more generally, do
we really need "struct page *"?

static struct page *__dma_alloc_from_pool(struct device *dev, size_t size,
		struct gen_pool *pool, void **cpu_addr,
		bool (*phys_addr_ok)(struct device *, phys_addr_t, size_t))
{
...
	*cpu_addr = (void *)addr;
	memset(*cpu_addr, 0, size);
	return pfn_to_page(__phys_to_pfn(phys));
}

Why 

> +	}
>  
>  	/* we always manually zero the memory once we are done */
>  	page = __dma_direct_alloc_pages(dev, size, gfp & ~__GFP_ZERO, true);
> @@ -357,7 +359,7 @@ struct page *dma_direct_alloc_pages(struct device *dev, size_t size,
>  	void *ret;
>  
>  	if (force_dma_unencrypted(dev) && dma_direct_use_pool(dev, gfp))
> -		return dma_direct_alloc_from_pool(dev, size, dma_handle, gfp);
> +		return dma_direct_alloc_from_pool(dev, size, dma_handle, &ret, gfp);
>  
>  	page = __dma_direct_alloc_pages(dev, size, gfp, false);
>  	if (!page)
> -- 
> 2.43.0
> 
>