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Thu, 15 Apr 2021 18:08:37 +0000 (UTC) Received: from carbon (unknown [10.36.110.19]) by smtp.corp.redhat.com (Postfix) with ESMTP id 8013D13487; Thu, 15 Apr 2021 18:08:33 +0000 (UTC) Date: Thu, 15 Apr 2021 20:08:32 +0200 From: Jesper Dangaard Brouer To: David Laight Cc: 'Matthew Wilcox' , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "netdev@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , "linux-arm-kernel@lists.infradead.org" , "linux-mips@vger.kernel.org" , Ilias Apalodimas , Matteo Croce , Grygorii Strashko , Arnd Bergmann , "Christoph Hellwig" , brouer@redhat.com Subject: Re: [PATCH 1/1] mm: Fix struct page layout on 32-bit systems Message-ID: <20210415200832.32796445@carbon> In-Reply-To: References: <20210410205246.507048-1-willy@infradead.org> <20210410205246.507048-2-willy@infradead.org> <20210411114307.5087f958@carbon> <20210411103318.GC2531743@casper.infradead.org> <20210412011532.GG2531743@casper.infradead.org> <20210414101044.19da09df@carbon> <20210414115052.GS2531743@casper.infradead.org> <20210414211322.3799afd4@carbon> <20210414213556.GY2531743@casper.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Rspamd-Queue-Id: CBD6EE000125 X-Stat-Signature: inkupuzjkykazoed5zfnxdjqtjaorygj X-Rspamd-Server: rspam02 Received-SPF: none (redhat.com>: No applicable sender policy available) receiver=imf21; identity=mailfrom; envelope-from=""; helo=us-smtp-delivery-124.mimecast.com; client-ip=216.205.24.124 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1618510121-834762 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, 14 Apr 2021 21:56:39 +0000 David Laight wrote: > From: Matthew Wilcox > > Sent: 14 April 2021 22:36 > > > > On Wed, Apr 14, 2021 at 09:13:22PM +0200, Jesper Dangaard Brouer wrote: > > > (If others want to reproduce). First I could not reproduce on ARM32. > > > Then I found out that enabling CONFIG_XEN on ARCH=arm was needed to > > > cause the issue by enabling CONFIG_ARCH_DMA_ADDR_T_64BIT. > > > > hmmm ... you should be able to provoke it by enabling ARM_LPAE, > > which selects PHYS_ADDR_T_64BIT, and > > > > config ARCH_DMA_ADDR_T_64BIT > > def_bool 64BIT || PHYS_ADDR_T_64BIT > > > > > struct page { > > > long unsigned int flags; /* 0 4 */ > > > > > > /* XXX 4 bytes hole, try to pack */ > > > > > > union { > > > struct { > > > struct list_head lru; /* 8 8 */ > > > struct address_space * mapping; /* 16 4 */ > > > long unsigned int index; /* 20 4 */ > > > long unsigned int private; /* 24 4 */ > > > }; /* 8 20 */ > > > struct { > > > dma_addr_t dma_addr > > Adding __packed here will remove the 4 byte hole before the union > and the compiler seems clever enough to know that anything following > a 'long' must also be 'long' aligned. Played with __packed in below patch, and I can confirm it seems to work. > So you don't get anything horrid like byte accesses. > On 64bit dma_addr will remain 64bit aligned. > On arm32 dma_addr will be 32bit aligned - but forcing two 32bit access > won't make any difference. See below patch. Where I swap32 the dma address to satisfy page->compound having bit zero cleared. (It is the simplest fix I could come up with). [PATCH] page_pool: handling 32-bit archs with 64-bit dma_addr_t From: Jesper Dangaard Brouer Workaround for storing 64-bit DMA-addr on 32-bit machines in struct page. The page->dma_addr share area with page->compound_head which use bit zero to mark compound pages. This is okay, as DMA-addr are aligned pointers which have bit zero cleared. In the 32-bit case, page->compound_head is 32-bit. Thus, when dma_addr_t is 64-bit it will be located in top 32-bit. Solve by swapping dma_addr 32-bit segments. Signed-off-by: Jesper Dangaard Brouer --- include/linux/mm_types.h | 2 +- include/linux/types.h | 1 + include/net/page_pool.h | 21 ++++++++++++++++++++- net/core/page_pool.c | 8 +++++--- 4 files changed, 27 insertions(+), 5 deletions(-) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 6613b26a8894..27406e3b1e1b 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -100,7 +100,7 @@ struct page { * @dma_addr: might require a 64-bit value even on * 32-bit architectures. */ - dma_addr_t dma_addr; + dma_addr_t dma_addr __packed; }; struct { /* slab, slob and slub */ union { diff --git a/include/linux/types.h b/include/linux/types.h index ac825ad90e44..65fd5d630016 100644 --- a/include/linux/types.h +++ b/include/linux/types.h @@ -141,6 +141,7 @@ typedef u64 blkcnt_t; */ #ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT typedef u64 dma_addr_t; +//typedef u64 __attribute__((aligned(sizeof(void *)))) dma_addr_t; #else typedef u32 dma_addr_t; #endif diff --git a/include/net/page_pool.h b/include/net/page_pool.h index b5b195305346..c2329088665c 100644 --- a/include/net/page_pool.h +++ b/include/net/page_pool.h @@ -196,9 +196,28 @@ static inline void page_pool_recycle_direct(struct page_pool *pool, page_pool_put_full_page(pool, page, true); } +static inline +dma_addr_t page_pool_dma_addr_read(dma_addr_t dma_addr) +{ + /* Workaround for storing 64-bit DMA-addr on 32-bit machines in struct + * page. The page->dma_addr share area with page->compound_head which + * use bit zero to mark compound pages. This is okay, as DMA-addr are + * aligned pointers which have bit zero cleared. + * + * In the 32-bit case, page->compound_head is 32-bit. Thus, when + * dma_addr_t is 64-bit it will be located in top 32-bit. Solve by + * swapping dma_addr 32-bit segments. + */ +#ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT + if (sizeof(long unsigned int) == 4) /* 32-bit system */ + dma_addr = (dma_addr << 32) | (dma_addr >> 32); +#endif + return dma_addr; +} + static inline dma_addr_t page_pool_get_dma_addr(struct page *page) { - return page->dma_addr; + return page_pool_dma_addr_read(page->dma_addr); } static inline bool is_page_pool_compiled_in(void) diff --git a/net/core/page_pool.c b/net/core/page_pool.c index ad8b0707af04..813598ea23f6 100644 --- a/net/core/page_pool.c +++ b/net/core/page_pool.c @@ -174,8 +174,10 @@ static void page_pool_dma_sync_for_device(struct page_pool *pool, struct page *page, unsigned int dma_sync_size) { + dma_addr_t dma = page_pool_dma_addr_read(page->dma_addr); + dma_sync_size = min(dma_sync_size, pool->p.max_len); - dma_sync_single_range_for_device(pool->p.dev, page->dma_addr, + dma_sync_single_range_for_device(pool->p.dev, dma, pool->p.offset, dma_sync_size, pool->p.dma_dir); } @@ -226,7 +228,7 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool, put_page(page); return NULL; } - page->dma_addr = dma; + page->dma_addr = page_pool_dma_addr_read(dma); if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV) page_pool_dma_sync_for_device(pool, page, pool->p.max_len); @@ -294,7 +296,7 @@ void page_pool_release_page(struct page_pool *pool, struct page *page) */ goto skip_dma_unmap; - dma = page->dma_addr; + dma = page_pool_dma_addr_read(page->dma_addr); /* When page is unmapped, it cannot be returned our pool */ dma_unmap_page_attrs(pool->p.dev, dma, -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer