Commit 90de47f0 authored by Yunsheng Lin's avatar Yunsheng Lin Committed by Jakub Kicinski
Browse files

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

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: default avatarAlexander Lobakin <aleksander.lobakin@intel.com>
Signed-off-by: default avatarYunsheng 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: default avatarJakub Kicinski <kuba@kernel.org>
parent e411a8e3

include/linux/mm_types.h

+1 −12
Original line number Diff line number Diff line
@@ -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 */

		};

include/net/page_pool/helpers.h

+14 −6
Original line number Diff line number Diff line
@@ -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)

net/core/page_pool.c

+9 −5
Original line number Diff line number Diff line
@@ -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,