From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga11.intel.com (mga11.intel.com [192.55.52.93]) by dpdk.org (Postfix) with ESMTP id 06F4958F6 for ; Wed, 12 Jul 2017 09:31:42 +0200 (CEST) Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga102.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 12 Jul 2017 00:31:41 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.40,347,1496127600"; d="scan'208";a="1194354417" Received: from smonroyx-mobl.ger.corp.intel.com (HELO [10.237.221.5]) ([10.237.221.5]) by fmsmga002.fm.intel.com with ESMTP; 12 Jul 2017 00:31:40 -0700 To: "Tan, Jianfeng" , Stephen Hemminger , "dev@dpdk.org" References: <20170711011242.4606-1-stephen@networkplumber.org> <3f48cbd3-1e60-5a92-3929-7ba06e3cc69c@intel.com> From: Sergio Gonzalez Monroy Message-ID: Date: Wed, 12 Jul 2017 08:31:40 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [dpdk-dev] [RFC] pci: force address of mappings in secondary process X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 12 Jul 2017 07:31:43 -0000 On 12/07/2017 03:45, Tan, Jianfeng wrote: > >> -----Original Message----- >> From: Gonzalez Monroy, Sergio >> Sent: Tuesday, July 11, 2017 7:36 PM >> To: Tan, Jianfeng; Stephen Hemminger; dev@dpdk.org >> Subject: Re: [dpdk-dev] [RFC] pci: force address of mappings in secondary >> process >> >> On 11/07/2017 02:56, Tan, Jianfeng wrote: >>>> -----Original Message----- >>>> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Stephen >>>> Hemminger >>>> Sent: Tuesday, July 11, 2017 9:13 AM >>>> To: dev@dpdk.org >>>> Cc: Stephen Hemminger >>>> Subject: [dpdk-dev] [RFC] pci: force address of mappings in secondary >>>> process >>>> >>>> The PCI memory resources in the secondary process should be in >>>> the exact same location as the primary process. Otherwise >>>> there is a risk of a stray pointer. >>>> >>>> Not sure if this is right, but it looks like a potential >>>> problem. >>>> >>>> --- >>>> lib/librte_eal/common/eal_common_pci_uio.c | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/lib/librte_eal/common/eal_common_pci_uio.c >>>> b/lib/librte_eal/common/eal_common_pci_uio.c >>>> index 367a6816dcb8..2156b1a436c4 100644 >>>> --- a/lib/librte_eal/common/eal_common_pci_uio.c >>>> +++ b/lib/librte_eal/common/eal_common_pci_uio.c >>>> @@ -77,7 +77,7 @@ pci_uio_map_secondary(struct rte_pci_device *dev) >>>> >>>> void *mapaddr = pci_map_resource(uio_res- >>>>> maps[i].addr, >>>> fd, (off_t)uio_res->maps[i].offset, >>>> - (size_t)uio_res->maps[i].size, 0); >>>> + (size_t)uio_res->maps[i].size, >>>> MAP_FIXED); >>>> /* fd is not needed in slave process, close it */ >>>> close(fd); >>>> if (mapaddr != uio_res->maps[i].addr) { >>>> -- >>>> 2.11.0 >>> +1 for this RFC. I also once encounter such problem, and I use the same >> way to solve it. The addr parameter of mmap() syscall is only a hint instead of >> a must even the VMA is not occupied yet. >>> Thanks, >>> Jianfeng >> How do you know the VMA is not occupied? > I did by check /proc/self/maps. > >> I think the risk here is that the dynamic linker loaded some shared >> library in that VMA, and forcing MAP_FIXED is not a safe solution. >> What I have observed is that Linux will return a different VMA than the >> one hinted when there is already a mapping in the requested/hinted VMA. > IMO, that's not the target of this RFC. The target is to solve the situation (in current primary/secondary model) that kernel will not use the addr even there's no VMA on that addr. This is my understanding, Stephen, please correct me if I'm wrong. The point I was trying to make is, that you do not know if there is a mapping or not in that address, and by using MAP_FIXED it will unmap whatever was in there before. So unless you parse /proc/self/maps and check that the VMA range is not being used, forcing MAP_FIXED is not safe. >> I reckon this is a similar issue as we have with the multi-process model >> when we do not get the VMA requested for the huge-pages. >> AFAIK we do not have a robust solution for this issue other than restart >> the program and hope the dynamic linker does not map anything in the VMA >> ranges that we need to map from the primary. This is also assuming that >> the application does not allocate memory and maps things before calling >> eal_init as it could potentially use VMA ranges that we need in the >> secondary process. > This is another problem. It is the same problem, VMA ranges that we need to map being already used. Thanks, Sergio >> The proposal for new secondary process model would solve these issues: >> http://dpdk.org/ml/archives/dev/2017-May/066147.html > And yes, this might happen to solve the targeted issue in this RFC. But before the new model is out, this patch seems a workable way for the original issue. > > Thanks, > Jianfeng > >> Thanks, >> Sergio