From mboxrd@z Thu Jan 1 00:00:00 1970 From: tndave Subject: Re: i40e: Kernel unaligned access due to 'struct i40e_dma_mem' being 'packed' Date: Fri, 29 Jan 2016 14:47:27 -0800 Message-ID: <56ABEBFF.6030004@oracle.com> References: <56A973D6.4060202@oracle.com> <20160128.015643.125847430094859447.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed 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: David Miller Return-path: Received: from aserp1040.oracle.com ([141.146.126.69]:36583 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753171AbcA2Wrg (ORCPT ); Fri, 29 Jan 2016 17:47:36 -0500 In-Reply-To: <20160128.015643.125847430094859447.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-ID: On 01/27/2016 10:56 PM, David Miller wrote: > 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. True. For the same reason I want to clarify if __packed is actually needed? instead of fixing it with get_unaligned/put_unaligned()! -Tushar >