From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: netdev@vger.kernel.org, linux-mm@kvack.org,
"Toke Høiland-Jørgensen" <toke@toke.dk>,
"Ilias Apalodimas" <ilias.apalodimas@linaro.org>,
willy@infradead.org, "Saeed Mahameed" <saeedm@mellanox.com>,
"Alexander Duyck" <alexander.duyck@gmail.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
mgorman@techsingularity.net,
"David S. Miller" <davem@davemloft.net>,
"Tariq Toukan" <tariqt@mellanox.com>
Subject: Re: [net-next PATCH V3 1/3] mm: add dma_addr_t to struct page
Date: Wed, 29 Apr 2020 03:38:43 +0300 [thread overview]
Message-ID: <20200429003843.rh2pasek7v5o3h63@box> (raw)
In-Reply-To: <155002294008.5597.13759027075590385810.stgit@firesoul>
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@redhat.com>
> Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
> Acked-by: Andrew Morton <akpm@linux-foundation.org>
> ---
> 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
next prev parent reply other threads:[~2020-04-29 0:38 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-13 1:55 [net-next PATCH V3 0/3] Fix page_pool API and dma address storage Jesper Dangaard Brouer
2019-02-13 1:55 ` [net-next PATCH V3 1/3] mm: add dma_addr_t to struct page Jesper Dangaard Brouer
2020-04-29 0:38 ` Kirill A. Shutemov [this message]
2020-04-29 1:54 ` Matthew Wilcox
2019-02-13 1:55 ` [net-next PATCH V3 2/3] net: page_pool: don't use page->private to store dma_addr_t Jesper Dangaard Brouer
2019-02-13 1:55 ` [net-next PATCH V3 3/3] page_pool: use DMA_ATTR_SKIP_CPU_SYNC for DMA mappings Jesper Dangaard Brouer
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