Replacement patch to fix compiler warning.
From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Date: Fri, 16 Apr 2021 16:34:55 -0400
Subject: [PATCH 1/2] mm: Fix struct page layout on 32-bit systems
To: brouer@xxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx,
linux-mm@xxxxxxxxx,
netdev@xxxxxxxxxxxxxxx,
linuxppc-dev@xxxxxxxxxxxxxxxx,
linux-arm-kernel@xxxxxxxxxxxxxxxxxxx,
linux-mips@xxxxxxxxxxxxxxx,
ilias.apalodimas@xxxxxxxxxx,
mcroce@xxxxxxxxxxxxxxxxxxx,
grygorii.strashko@xxxxxx,
arnd@xxxxxxxxxx,
hch@xxxxxx,
linux-snps-arc@xxxxxxxxxxxxxxxxxxx,
mhocko@xxxxxxxxxx,
mgorman@xxxxxxx
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@xxxxxxxxxxxxx>
---
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;
}
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
