From: Ilias Apalodimas <ilias.apalodimas@linaro.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: arnd@kernel.org, grygorii.strashko@ti.com,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mips@vger.kernel.org, mhocko@kernel.org,
linux-mm@kvack.org, mgorman@suse.de, brouer@redhat.com,
mcroce@linux.microsoft.com, linux-snps-arc@lists.infradead.org,
linuxppc-dev@lists.ozlabs.org, hch@lst.de,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 1/2] mm: Fix struct page layout on 32-bit systems
Date: Sat, 17 Apr 2021 21:32:06 +0300 [thread overview]
Message-ID: <YHspptFx+T588KcG@apalos.home> (raw)
In-Reply-To: <20210417024522.GP2531743@casper.infradead.org>
Hi Matthew,
On Sat, Apr 17, 2021 at 03:45:22AM +0100, Matthew Wilcox wrote:
>
> Replacement patch to fix compiler warning.
>
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> Date: Fri, 16 Apr 2021 16:34:55 -0400
> Subject: [PATCH 1/2] mm: Fix struct page layout on 32-bit systems
> To: brouer@redhat.com
> Cc: linux-kernel@vger.kernel.org,
> linux-mm@kvack.org,
> netdev@vger.kernel.org,
> linuxppc-dev@lists.ozlabs.org,
> linux-arm-kernel@lists.infradead.org,
> linux-mips@vger.kernel.org,
> ilias.apalodimas@linaro.org,
> mcroce@linux.microsoft.com,
> grygorii.strashko@ti.com,
> arnd@kernel.org,
> hch@lst.de,
> linux-snps-arc@lists.infradead.org,
> mhocko@kernel.org,
> mgorman@suse.de
>
> 32-bit architectures which expect 8-byte alignment for 8-byte integers
> and need 64-bit DMA addresses (arc, arm, mips, ppc) had their struct
> page inadvertently expanded in 2019. When the dma_addr_t was added,
> it forced the alignment of the union to 8 bytes, which inserted a 4 byte
> gap between 'flags' and the union.
>
> Fix this by storing the dma_addr_t in one or two adjacent unsigned longs.
> This restores the alignment to that of an unsigned long, and also fixes a
> potential problem where (on a big endian platform), the bit used to denote
> PageTail could inadvertently get set, and a racing get_user_pages_fast()
> could dereference a bogus compound_head().
>
> Fixes: c25fff7171be ("mm: add dma_addr_t to struct page")
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
> include/linux/mm_types.h | 4 ++--
> include/net/page_pool.h | 12 +++++++++++-
> net/core/page_pool.c | 12 +++++++-----
> 3 files changed, 20 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 6613b26a8894..5aacc1c10a45 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -97,10 +97,10 @@ struct page {
> };
> struct { /* page_pool used by netstack */
> /**
> - * @dma_addr: might require a 64-bit value even on
> + * @dma_addr: might require a 64-bit value on
> * 32-bit architectures.
> */
> - dma_addr_t dma_addr;
> + unsigned long dma_addr[2];
> };
> struct { /* slab, slob and slub */
> union {
> diff --git a/include/net/page_pool.h b/include/net/page_pool.h
> index b5b195305346..ad6154dc206c 100644
> --- a/include/net/page_pool.h
> +++ b/include/net/page_pool.h
> @@ -198,7 +198,17 @@ static inline void page_pool_recycle_direct(struct page_pool *pool,
>
> static inline dma_addr_t page_pool_get_dma_addr(struct page *page)
> {
> - return page->dma_addr;
> + dma_addr_t ret = page->dma_addr[0];
> + if (sizeof(dma_addr_t) > sizeof(unsigned long))
> + ret |= (dma_addr_t)page->dma_addr[1] << 16 << 16;
> + return ret;
> +}
> +
> +static inline void page_pool_set_dma_addr(struct page *page, dma_addr_t addr)
> +{
> + page->dma_addr[0] = addr;
> + if (sizeof(dma_addr_t) > sizeof(unsigned long))
> + page->dma_addr[1] = addr >> 16 >> 16;
The 'error' that was reported will never trigger right?
I assume this was compiled with dma_addr_t as 32bits (so it triggered the
compilation error), but the if check will never allow this codepath to run.
If so can we add a comment explaining this, since none of us will remember why
in 6 months from now?
> }
>
> static inline bool is_page_pool_compiled_in(void)
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index ad8b0707af04..f014fd8c19a6 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -174,8 +174,10 @@ static void page_pool_dma_sync_for_device(struct page_pool *pool,
> struct page *page,
> unsigned int dma_sync_size)
> {
> + dma_addr_t dma_addr = page_pool_get_dma_addr(page);
> +
> dma_sync_size = min(dma_sync_size, pool->p.max_len);
> - dma_sync_single_range_for_device(pool->p.dev, page->dma_addr,
> + dma_sync_single_range_for_device(pool->p.dev, dma_addr,
> pool->p.offset, dma_sync_size,
> pool->p.dma_dir);
> }
> @@ -226,7 +228,7 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
> put_page(page);
> return NULL;
> }
> - page->dma_addr = dma;
> + page_pool_set_dma_addr(page, dma);
>
> if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
> page_pool_dma_sync_for_device(pool, page, pool->p.max_len);
> @@ -294,13 +296,13 @@ void page_pool_release_page(struct page_pool *pool, struct page *page)
> */
> goto skip_dma_unmap;
>
> - dma = page->dma_addr;
> + dma = page_pool_get_dma_addr(page);
>
> - /* When page is unmapped, it cannot be returned our pool */
> + /* When page is unmapped, it cannot be returned to our pool */
> dma_unmap_page_attrs(pool->p.dev, dma,
> PAGE_SIZE << pool->p.order, pool->p.dma_dir,
> DMA_ATTR_SKIP_CPU_SYNC);
> - page->dma_addr = 0;
> + page_pool_set_dma_addr(page, 0);
> skip_dma_unmap:
> /* This may be the last page returned, releasing the pool, so
> * it is not safe to reference pool afterwards.
> --
> 2.30.2
>
Thanks
/Ilias
next prev parent reply other threads:[~2021-04-17 18:32 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-16 23:07 [PATCH 0/2] Change struct page layout for page_pool Matthew Wilcox (Oracle)
2021-04-16 23:07 ` [PATCH 1/2] mm: Fix struct page layout on 32-bit systems Matthew Wilcox (Oracle)
2021-04-17 1:08 ` kernel test robot
2021-04-17 2:45 ` Matthew Wilcox
2021-04-17 18:32 ` Ilias Apalodimas [this message]
2021-04-17 20:22 ` Matthew Wilcox
2021-04-18 11:21 ` Ilias Apalodimas
2021-04-17 21:18 ` David Laight
2021-04-17 22:45 ` Matthew Wilcox
2021-04-20 2:48 ` Vineet Gupta
2021-04-20 3:10 ` Matthew Wilcox
2021-04-20 7:07 ` Arnd Bergmann
2021-04-20 21:14 ` Vineet Gupta
2021-04-20 21:20 ` Arnd Bergmann
2021-04-21 5:50 ` hch
2021-04-21 8:43 ` David Laight
2021-04-21 8:58 ` Arnd Bergmann
2021-04-20 7:39 ` Geert Uytterhoeven
2021-04-20 8:39 ` David Laight
2021-04-20 11:32 ` Matthew Wilcox
2021-04-17 7:34 ` Jesper Dangaard Brouer
2021-04-20 7:21 ` Rasmus Villemoes
2021-04-16 23:07 ` [PATCH 2/2] mm: Indicate pfmemalloc pages in compound_head Matthew Wilcox (Oracle)
2021-04-17 21:13 ` David Laight
2021-04-17 21:28 ` Matthew Wilcox
2021-04-20 4:03 ` [PATCH 0/2] Change struct page layout for page_pool Michael Ellerman
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