Re: [PATCH net] page_pool: Revert "page_pool: disable dma mapping support..."

[Jesper Dangaard Brouer]

Added CC: linux-mm@xxxxxxxxx

On 17/11/2021 08.56, Yunsheng Lin wrote:
> This reverts commit d00e60ee54b12de945b8493cf18c1ada9e422514.
>
> As reported by Guillaume in [1]:
> Enabling LPAE always enables CONFIG_ARCH_DMA_ADDR_T_64BIT
> in 32-bit systems, which breaks the bootup proceess when a
> ethernet driver is using page pool with PP_FLAG_DMA_MAP flag.
> As we were hoping we had no active consumers for such system
> when we removed the dma mapping support, and LPAE seems like
> a common feature for 32 bits system, so revert it.
>
> 1. https://www.spinics.net/lists/netdev/msg779890.html
>
> Fixes: d00e60ee54b1 ("page_pool: disable dma mapping support for 32-bit arch with 64-bit DMA")
> Signed-off-by: Yunsheng Lin <linyunsheng@xxxxxxxxxx>
> ---
>   include/linux/mm_types.h | 13 ++++++++++++-
>   include/net/page_pool.h  | 12 +++++++++++-
>   net/core/page_pool.c     | 10 ++++------
>   3 files changed, 27 insertions(+), 8 deletions(-)

Acked-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>

Too bad that we have to keep this code-uglyness in struct page, and 
handling in page_pool.


> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index bb8c6f5f19bc..c3a6e6209600 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -105,7 +105,18 @@ struct page {
>   			struct page_pool *pp;
>   			unsigned long _pp_mapping_pad;
>   			unsigned long dma_addr;
> -			atomic_long_t pp_frag_count;
> +			union {
> +				/**
> +				 * dma_addr_upper: might require a 64-bit
> +				 * value on 32-bit architectures.
> +				 */
> +				unsigned long dma_addr_upper;
> +				/**
> +				 * For frag page support, not supported in
> +				 * 32-bit architectures with 64-bit DMA.
> +				 */
> +				atomic_long_t pp_frag_count;
> +			};
>   		};
>   		struct {	/* slab, slob and slub */
>   			union {
> diff --git a/include/net/page_pool.h b/include/net/page_pool.h
> index 3855f069627f..a4082406a003 100644
> --- a/include/net/page_pool.h
> +++ b/include/net/page_pool.h
> @@ -216,14 +216,24 @@ static inline void page_pool_recycle_direct(struct page_pool *pool,
>   	page_pool_put_full_page(pool, page, true);
>   }
>   
> +#define PAGE_POOL_DMA_USE_PP_FRAG_COUNT	\
> +		(sizeof(dma_addr_t) > sizeof(unsigned long))
> +
>   static inline dma_addr_t page_pool_get_dma_addr(struct page *page)
>   {
> -	return page->dma_addr;
> +	dma_addr_t ret = page->dma_addr;
> +
> +	if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT)
> +		ret |= (dma_addr_t)page->dma_addr_upper << 16 << 16;
> +
> +	return ret;
>   }
>   
>   static inline void page_pool_set_dma_addr(struct page *page, dma_addr_t addr)
>   {
>   	page->dma_addr = addr;
> +	if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT)
> +		page->dma_addr_upper = upper_32_bits(addr);
>   }
>   
>   static inline void page_pool_set_frag_count(struct page *page, long nr)
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index 9b60e4301a44..1a6978427d6c 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -49,12 +49,6 @@ static int page_pool_init(struct page_pool *pool,
>   	 * which is the XDP_TX use-case.
>   	 */
>   	if (pool->p.flags & PP_FLAG_DMA_MAP) {
> -		/* DMA-mapping is not supported on 32-bit systems with
> -		 * 64-bit DMA mapping.
> -		 */
> -		if (sizeof(dma_addr_t) > sizeof(unsigned long))
> -			return -EOPNOTSUPP;
> -
>   		if ((pool->p.dma_dir != DMA_FROM_DEVICE) &&
>   		    (pool->p.dma_dir != DMA_BIDIRECTIONAL))
>   			return -EINVAL;
> @@ -75,6 +69,10 @@ static int page_pool_init(struct page_pool *pool,
>   		 */
>   	}
>   
> +	if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT &&
> +	    pool->p.flags & PP_FLAG_PAGE_FRAG)
> +		return -EINVAL;
> +
>   	if (ptr_ring_init(&pool->ring, ring_qsize, GFP_KERNEL) < 0)
>   		return -ENOMEM;
>