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page_pool: fragment API support for 32-bit arch with 64-bit DMA

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Currently page_pool_alloc_frag() is not supported in 32-bit
arch with 64-bit DMA because of the overlap issue between
pp_frag_count and dma_addr_upper in 'struct page' for those
arches, which seems to be quite common, see [1], which means
driver may need to handle it when using fragment API.

It is assumed that the combination of the above arch with an
address space >16TB does not exist, as all those arches have
64b equivalent, it seems logical to use the 64b version for a
system with a large address space. It is also assumed that dma
address is page aligned when we are dma mapping a page aligned
buffer, see [2].

That means we're storing 12 bits of 0 at the lower end for a
dma address, we can reuse those bits for the above arches to
support 32b+12b, which is 16TB of memory.

If we make a wrong assumption, a warning is emitted so that
user can report to us.

1. https://lore.kernel.org/all/20211117075652.58299-1-linyunsheng@huawei.com/
2. https://lore.kernel.org/all/20230818145145.4b357c89@kernel.org/

Tested-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
CC: Lorenzo Bianconi <lorenzo@kernel.org>
CC: Alexander Duyck <alexander.duyck@gmail.com>
CC: Liang Chen <liangchen.linux@gmail.com>
CC: Guillaume Tucker <guillaume.tucker@collabora.com>
CC: Matthew Wilcox <willy@infradead.org>
CC: Linux-MM <linux-mm@kvack.org>
Link: https://lore.kernel.org/r/20231013064827.61135-2-linyunsheng@huawei.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Yunsheng Lin 2023-10-13 14:48:21 +08:00 committed by Jakub Kicinski
parent e411a8e3bb
commit 90de47f020
3 changed files with 24 additions and 23 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

11
include/linux/mm_types.h
View file

@ -125,19 +125,8 @@ struct page {
struct page_pool *pp;
unsigned long _pp_mapping_pad;
unsigned long dma_addr;
union {
/**
* dma_addr_upper: might require a 64-bit
* value on 32-bit architectures.
*/
unsigned long dma_addr_upper;
/**
* For frag page support, not supported in
* 32-bit architectures with 64-bit DMA.
*/
atomic_long_t pp_frag_count;
};
};
struct { /* Tail pages of compound page */
unsigned long compound_head; /* Bit zero is set */
};

20
include/net/page_pool/helpers.h
View file

@ -197,7 +197,7 @@ static inline void page_pool_recycle_direct(struct page_pool *pool,
page_pool_put_full_page(pool, page, true);
}
#define PAGE_POOL_DMA_USE_PP_FRAG_COUNT \
#define PAGE_POOL_32BIT_ARCH_WITH_64BIT_DMA \
(sizeof(dma_addr_t) > sizeof(unsigned long))
/**
@ -211,17 +211,25 @@ static inline dma_addr_t page_pool_get_dma_addr(struct page *page)
{
dma_addr_t ret = page->dma_addr;
if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT)
ret |= (dma_addr_t)page->dma_addr_upper << 16 << 16;
if (PAGE_POOL_32BIT_ARCH_WITH_64BIT_DMA)
ret <<= PAGE_SHIFT;
return ret;
}
static inline void page_pool_set_dma_addr(struct page *page, dma_addr_t addr)
static inline bool page_pool_set_dma_addr(struct page *page, dma_addr_t addr)
{
if (PAGE_POOL_32BIT_ARCH_WITH_64BIT_DMA) {
page->dma_addr = addr >> PAGE_SHIFT;
/* We assume page alignment to shave off bottom bits,
* if this "compression" doesn't work we need to drop.
*/
return addr != (dma_addr_t)page->dma_addr << PAGE_SHIFT;
}
page->dma_addr = addr;
if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT)
page->dma_addr_upper = upper_32_bits(addr);
return false;
}
static inline bool page_pool_put(struct page_pool *pool)

14
net/core/page_pool.c
View file

@ -211,10 +211,6 @@ static int page_pool_init(struct page_pool *pool,
*/
}
if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT &&
pool->p.flags & PP_FLAG_PAGE_FRAG)
return -EINVAL;
#ifdef CONFIG_PAGE_POOL_STATS
pool->recycle_stats = alloc_percpu(struct page_pool_recycle_stats);
if (!pool->recycle_stats)
@ -359,12 +355,20 @@ static bool page_pool_dma_map(struct page_pool *pool, struct page *page)
if (dma_mapping_error(pool->p.dev, dma))
return false;
page_pool_set_dma_addr(page, dma);
if (page_pool_set_dma_addr(page, dma))
goto unmap_failed;
if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
page_pool_dma_sync_for_device(pool, page, pool->p.max_len);
return true;
unmap_failed:
WARN_ON_ONCE("unexpected DMA address, please report to netdev@");
dma_unmap_page_attrs(pool->p.dev, dma,
PAGE_SIZE << pool->p.order, pool->p.dma_dir,
DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_WEAK_ORDERING);
return false;
}
static void page_pool_set_pp_info(struct page_pool *pool,