On 2023/9/15 16:28, Jesper Dangaard Brouer wrote: > Hi Lin, > > This looks reasonable, but given you are changing struct-page > (include/linux/mm_types.h) we need to MM-list <linux-mm@xxxxxxxxx>. > Also Cc Wilcox. > > I think it was Ilias and Duyck that validated the assumptions, last time > this patch was discussed. Thus I want to see their review before this is > applied. FWIW, PAGE_SIZE aligned buffer being PAGE_SIZE aligned in DMA is validated by Duyck: https://lore.kernel.org/all/CAKgT0UfeUAUQpEffxnkc+gzXsjOrHkuMgxU_Aw0VXSJYKzaovQ@xxxxxxxxxxxxxx/ And I had done researching to find out there seems to be no combination of the above arch with an address space >16TB: https://lore.kernel.org/all/2b570282-24f8-f23b-1ff7-ad836794baa9@xxxxxxxxxx/ > > -Jesper > > On 12/09/2023 10.31, Yunsheng Lin wrote: >> 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 frag 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 aliged >> 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@xxxxxxxxxx/ >> 2. https://lore.kernel.org/all/20230818145145.4b357c89@xxxxxxxxxx/ >> >> Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx> >> Signed-off-by: Yunsheng Lin <linyunsheng@xxxxxxxxxx> >> CC: Lorenzo Bianconi <lorenzo@xxxxxxxxxx> >> CC: Alexander Duyck <alexander.duyck@xxxxxxxxx> >> CC: Liang Chen <liangchen.linux@xxxxxxxxx> >> CC: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx> >> CC: Guillaume Tucker <guillaume.tucker@xxxxxxxxxxxxx> >> --- >> include/linux/mm_types.h | 13 +------------ >> include/net/page_pool/helpers.h | 20 ++++++++++++++------ >> net/core/page_pool.c | 14 +++++++++----- >> 3 files changed, 24 insertions(+), 23 deletions(-) >> >> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h >> index 36c5b43999e6..74b49c4c7a52 100644 >> --- a/include/linux/mm_types.h >> +++ b/include/linux/mm_types.h >> @@ -125,18 +125,7 @@ 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; >> - }; >> + atomic_long_t pp_frag_count; >> }; >> struct { /* Tail pages of compound page */ >> unsigned long compound_head; /* Bit zero is set */ >> diff --git a/include/net/page_pool/helpers.h b/include/net/page_pool/helpers.h >> index 94231533a369..8e1c85de4995 100644 >> --- a/include/net/page_pool/helpers.h >> +++ b/include/net/page_pool/helpers.h >> @@ -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) >> diff --git a/net/core/page_pool.c b/net/core/page_pool.c >> index 77cb75e63aca..8a9868ea5067 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 +355,20 @@ 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, > > . >
