From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755078AbeEaLYb (ORCPT ); Thu, 31 May 2018 07:24:31 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:40116 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755055AbeEaLY0 (ORCPT ); Thu, 31 May 2018 07:24:26 -0400 Subject: Re: [PATCH 0/7] add non-strict mode support for arm-smmu-v3 To: Zhen Lei , Will Deacon , Matthias Brugger , Rob Clark , Joerg Roedel , linux-mediatek , linux-arm-msm , linux-arm-kernel , iommu , linux-kernel Cc: Hanjun Guo , Libin , Guozhu Li , Xinwei Hu References: <1527752569-18020-1-git-send-email-thunder.leizhen@huawei.com> From: Robin Murphy Message-ID: Date: Thu, 31 May 2018 12:24:21 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <1527752569-18020-1-git-send-email-thunder.leizhen@huawei.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 31/05/18 08:42, Zhen Lei wrote: > In common, a IOMMU unmap operation follow the below steps: > 1. remove the mapping in page table of the specified iova range > 2. execute tlbi command to invalid the mapping which is cached in TLB > 3. wait for the above tlbi operation to be finished > 4. free the IOVA resource > 5. free the physical memory resource > > This maybe a problem when unmap is very frequently, the combination of tlbi > and wait operation will consume a lot of time. A feasible method is put off > tlbi and iova-free operation, when accumulating to a certain number or > reaching a specified time, execute only one tlbi_all command to clean up > TLB, then free the backup IOVAs. Mark as non-strict mode. > > But it must be noted that, although the mapping has already been removed in > the page table, it maybe still exist in TLB. And the freed physical memory > may also be reused for others. So a attacker can persistent access to memory > based on the just freed IOVA, to obtain sensible data or corrupt memory. So > the VFIO should always choose the strict mode. > > Some may consider put off physical memory free also, that will still follow > strict mode. But for the map_sg cases, the memory allocation is not controlled > by IOMMU APIs, so it is not enforceable. > > Fortunately, Intel and AMD have already applied the non-strict mode, and put > queue_iova() operation into the common file dma-iommu.c., and my work is based > on it. The difference is that arm-smmu-v3 driver will call IOMMU common APIs to > unmap, but Intel and AMD IOMMU drivers are not. > > Below is the performance data of strict vs non-strict for NVMe device: > Randomly Read IOPS: 146K(strict) vs 573K(non-strict) > Randomly Write IOPS: 143K(strict) vs 513K(non-strict) What hardware is this on? If it's SMMUv3 without MSIs (e.g. D05), then you'll still be using the rubbish globally-blocking sync implementation. If that is the case, I'd be very interested to see how much there is to gain from just improving that - I've had a patch kicking around for a while[1] (also on a rebased branch at [2]), but don't have the means for serious performance testing. Robin. [1] https://www.mail-archive.com/iommu@lists.linux-foundation.org/msg20576.html [2] git://linux-arm.org/linux-rm iommu/smmu > > > Zhen Lei (7): > iommu/dma: fix trival coding style mistake > iommu/arm-smmu-v3: fix the implementation of flush_iotlb_all hook > iommu: prepare for the non-strict mode support > iommu/amd: make sure TLB to be flushed before IOVA freed > iommu/dma: add support for non-strict mode > iommu/io-pgtable-arm: add support for non-strict mode > iommu/arm-smmu-v3: add support for non-strict mode > > drivers/iommu/amd_iommu.c | 2 +- > drivers/iommu/arm-smmu-v3.c | 16 ++++++++++++--- > drivers/iommu/arm-smmu.c | 2 +- > drivers/iommu/dma-iommu.c | 41 ++++++++++++++++++++++++++++++-------- > drivers/iommu/io-pgtable-arm-v7s.c | 6 +++--- > drivers/iommu/io-pgtable-arm.c | 28 ++++++++++++++------------ > drivers/iommu/io-pgtable.h | 2 +- > drivers/iommu/ipmmu-vmsa.c | 2 +- > drivers/iommu/msm_iommu.c | 2 +- > drivers/iommu/mtk_iommu.c | 2 +- > drivers/iommu/qcom_iommu.c | 2 +- > include/linux/iommu.h | 5 +++++ > 12 files changed, 76 insertions(+), 34 deletions(-) >