On Wed, Feb 13, 2019 at 02:55:40AM +0100, Jesper Dangaard Brouer wrote:
> The page_pool API is using page->private to store DMA addresses.
> As pointed out by David Miller we can't use that on 32-bit architectures
> with 64-bit DMA
>
> This patch adds a new dma_addr_t struct to allow storing DMA addresses
>
> Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
> Signed-off-by: Ilias Apalodimas <ilias.apalodimas@xxxxxxxxxx>
> Acked-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
> include/linux/mm_types.h | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 2c471a2c43fa..0a36a22228e7 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -95,6 +95,13 @@ struct page {
> */
> unsigned long private;
> };
> + struct { /* page_pool used by netstack */
> + /**
> + * @dma_addr: might require a 64-bit value even on
> + * 32-bit architectures.
> + */
> + dma_addr_t dma_addr;
> + };
[ I'm slow, but I've just noticed this change into struct page. ]
Is there a change that the dma_addr would have bit 0 set? If yes it may
lead to false-positive PageTail() and really strange behaviour.
I think it's better to put some padding into the struct to avoid aliasing
to compound_head.
See commit 1d798ca3f164 ("mm: make compound_head() robust") for context.
> struct { /* slab, slob and slub */
> union {
> struct list_head slab_list; /* uses lru */
>
--
Kirill A. Shutemov
