From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: i40e: Kernel unaligned access due to 'struct i40e_dma_mem' being 'packed' Date: Thu, 28 Jan 2016 01:56:43 -0500 (EST) Message-ID: <20160128.015643.125847430094859447.davem@davemloft.net> References: <56A973D6.4060202@oracle.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, jeffrey.t.kirsher@intel.com, jesse.brandeburg@intel.com, shannon.nelson@intel.com, carolyn.wyborny@intel.com, donald.c.skidmore@intel.com, bruce.w.allan@intel.com, john.ronciak@intel.com, mitch.a.williams@intel.com, intel-wired-lan@lists.osuosl.org To: tushar.n.dave@oracle.com Return-path: Received: from shards.monkeyblade.net ([149.20.54.216]:52648 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752292AbcA1G4r (ORCPT ); Thu, 28 Jan 2016 01:56:47 -0500 In-Reply-To: <56A973D6.4060202@oracle.com> Sender: netdev-owner@vger.kernel.org List-ID: From: tndave Date: Wed, 27 Jan 2016 17:50:14 -0800 > Hi, > > i40e driver has 'struct i40e_dma_mem' defined with 'packed' directive > causing kernel unaligned errors on sparc (when > 40e_allocate_dma_mem_d() > is being called) > > log_unaligned: 1031 callbacks suppressed > Kernel unaligned access at TPC[448ae8] > dma_4v_alloc_coherent+0x188/0x2e0 > Kernel unaligned access at TPC[448ae8] > dma_4v_alloc_coherent+0x188/0x2e0 > Kernel unaligned access at TPC[448ae8] > dma_4v_alloc_coherent+0x188/0x2e0 > Kernel unaligned access at TPC[448ae8] > dma_4v_alloc_coherent+0x188/0x2e0 > > This can be fixed with get_unaligned/put_unaligned(). However I don't > see 'struct i40e_dma_mem' is being directly shoved into NIC hardware. > But instead fields of the struct are being read and used for hardware > (e.g. dma_addr_t pa). For the test, I remove __packed, and i40e driver > and HW works fine. (of course kernel unaligned errors are gone too). > My question is, does 'struct i40e_dma_mem' required to be __packed? People get overzealoud with __packed. And even if it doesn't cause unaligned accesses like this, it generates terrible code (byte at a time accesses to words) on several architectures.