Re: [PATCH net-next 1/7] page_pool: disable dma mapping support for 32-bit arch with 64-bit DMA

From: Ilias Apalodimas
Date: Thu Sep 23 2021 - 05:10:50 EST


(+cc Matthew) but this looks safe to me.

On Wed, 22 Sept 2021 at 12:43, Yunsheng Lin <linyunsheng@xxxxxxxxxx> wrote:
>
> As the 32-bit arch with 64-bit DMA seems to rare those days,
> and page pool is carrying a lot of code and complexity for
> systems that possibly don't exist.
>
> So disable dma mapping support for such systems, if drivers
> really want to work on such systems, they have to implement
> their own DMA-mapping fallback tracking outside page_pool.
>
> 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, 8 insertions(+), 27 deletions(-)
>
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 7f8ee09c711f..436e0946d691 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -104,18 +104,7 @@ struct page {
> struct page_pool *pp;
> unsigned long _pp_mapping_pad;
> unsigned long dma_addr;
> - 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;
> - };
> + 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 a4082406a003..3855f069627f 100644
> --- a/include/net/page_pool.h
> +++ b/include/net/page_pool.h
> @@ -216,24 +216,14 @@ 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)
> {
> - 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;
> + return page->dma_addr;
> }
>
> 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 1a6978427d6c..a65bd7972e37 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -49,6 +49,12 @@ 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 -EINVAL;
> +
> if ((pool->p.dma_dir != DMA_FROM_DEVICE) &&
> (pool->p.dma_dir != DMA_BIDIRECTIONAL))
> return -EINVAL;
> @@ -69,10 +75,6 @@ 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;
>
> --
> 2.33.0
>

Reviewed-by: Ilias Apalodimas <ilias.apalodimas@xxxxxxxxxx>