Re: [PATCH 1/1] mm: Fix struct page layout on 32-bit systems

[Matthew Wilcox]

On Thu, Apr 15, 2021 at 08:08:32PM +0200, Jesper Dangaard Brouer wrote:
> +static inline
> +dma_addr_t page_pool_dma_addr_read(dma_addr_t dma_addr)
> +{
> +	/* Workaround for storing 64-bit DMA-addr on 32-bit machines in struct
> +	 * page.  The page->dma_addr share area with page->compound_head which
> +	 * use bit zero to mark compound pages. This is okay, as DMA-addr are
> +	 * aligned pointers which have bit zero cleared.
> +	 *
> +	 * In the 32-bit case, page->compound_head is 32-bit.  Thus, when
> +	 * dma_addr_t is 64-bit it will be located in top 32-bit.  Solve by
> +	 * swapping dma_addr 32-bit segments.
> +	 */
> +#ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT

#if defined(CONFIG_ARCH_DMA_ADDR_T_64BIT) && defined(__BIG_ENDIAN)
otherwise you'll create the problem on ARM that you're avoiding on PPC ...

I think you want to delete the word '_read' from this function name because
you're using it for both read and write.