Re: [PATCH net-next v7 1/6] page_pool: frag API support for 32-bit arch with 64-bit DMA
From: Jakub Kicinski <kuba@kernel.org>
Date: 2023-08-18 21:52:47
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Subsystem:
memory management - core, networking [general], page pool, the rest · Maintainers:
Andrew Morton, David Hildenbrand, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Jesper Dangaard Brouer, Ilias Apalodimas, Linus Torvalds
On Fri, 18 Aug 2023 09:12:09 +0300 Ilias Apalodimas wrote:
quoted
Right, IIUC we don't have enough space to fit dma_addr_t and the refcount, but if we store the dma addr on a shifted u32 instead of using dma_addr_t explicitly - the refcount should fit?struct page looks like this: unsigned long dma_addr; union { unsigned long dma_addr_upper; atomic_long_t pp_frag_count; };
I could be completely misunderstanding the problem. Let me show you the diff of what I was thinking more or less.
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 5e74ce4a28cd..58ffa8dc745f 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h@@ -126,11 +126,6 @@ struct page { 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.
diff --git a/include/net/page_pool/helpers.h b/include/net/page_pool/helpers.h
index 94231533a369..6f87a0fa2178 100644
--- a/include/net/page_pool/helpers.h
+++ b/include/net/page_pool/helpers.h@@ -212,16 +212,24 @@ 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; + 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) { + bool failed = false; + page->dma_addr = addr; - if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT) - page->dma_addr_upper = upper_32_bits(addr); + if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT) { + page->dma_addr >>= PAGE_SHIFT; + /* We assume page alignment to shave off bottom bits, + * if this "compression" doesn't work we need to drop. + */ + failed = addr != page->dma_addr << PAGE_SHIFT; + } + return failed; } static inline bool page_pool_put(struct page_pool *pool)
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 77cb75e63aca..9ea42e242a89 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c@@ -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 +355,19 @@ 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: + 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,