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

[Aneesh Kumar K.V <aneesh.kumar@kernel.org>]

Leon Romanovsky <leon@kernel.org> writes:

> 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
>

With CONFIG_DMA_DIRECT_REMAP the cpu_addr can be different from
page_address.

-aneesh