From 90de47f020db086f7929e09f64efd0cf627d6869 Mon Sep 17 00:00:00 2001 From: Yunsheng Lin Date: Fri, 13 Oct 2023 14:48:21 +0800 Subject: 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: Alexander Lobakin Signed-off-by: Yunsheng Lin CC: Lorenzo Bianconi CC: Alexander Duyck CC: Liang Chen CC: Guillaume Tucker CC: Matthew Wilcox CC: Linux-MM Link: https://lore.kernel.org/r/20231013064827.61135-2-linyunsheng@huawei.com Signed-off-by: Jakub Kicinski --- include/linux/mm_types.h | 13 +------------ 1 file changed, 1 insertion(+), 12 deletions(-) (limited to 'include/linux') 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 */ -- cgit v1.2.3