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Fri, 23 Apr 2021 18:20:05 +0000 Received: from [10.41.23.128] (172.20.145.6) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Fri, 23 Apr 2021 18:19:58 +0000 Subject: Re: [PATCH v14 00/13] SMMUv3 Nested Stage Setup (IOMMU part) To: Krishna Reddy , Jean-Philippe Brucker CC: "eric.auger@redhat.com" , "alex.williamson@redhat.com" , "eric.auger.pro@gmail.com" , "iommu@lists.linux-foundation.org" , "jiangkunkun@huawei.com" , "joro@8bytes.org" , "kvm@vger.kernel.org" , "kvmarm@lists.cs.columbia.edu" , "linux-kernel@vger.kernel.org" , "lushenming@huawei.com" , "maz@kernel.org" , "robin.murphy@arm.com" , "tn@semihalf.com" , "vivek.gautam@arm.com" , Vikram Sethi , "wangxingang5@huawei.com" , "will@kernel.org" , "zhangfei.gao@linaro.org" , "zhukeqian1@huawei.com" , Sachin Nikam , Bibek Basu , Shanker Donthineni , Sumit Gupta References: <1619103878-6664-1-git-send-email-sumitg@nvidia.com> <5a8825bc-286e-b316-515f-3bd3c9c70a80@nvidia.com> From: Sumit Gupta Message-ID: <467c95cd-3ba5-519e-cdac-9f477da86ecb@nvidia.com> Date: Fri, 23 Apr 2021 23:49:55 +0530 User-Agent: Mozilla/5.0 (X11; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 23 Apr 2021 18:20:05.3193 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: b097732a-0214-45a3-b625-08d906846b48 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.112.34];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: BN8NAM11FT056.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN9PR12MB5196 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org >>> Did that patch cause any issue, or is it just not needed on your system? >>> It fixes an hypothetical problem with the way ATS is implemented. >>> Maybe I actually observed it on an old software model, I don't >>> remember. Either way it's unlikely to go upstream but I'd like to know >>> if I should drop it from my tree. > >> Had to revert same patch "mm: notify remote TLBs when dirtying a PTE" to >> avoid below crash[1]. I am not sure about the cause yet. > > I have noticed this issue earlier with patch pointed here and root caused the issue as below. > It happens after vfio_mmap request from QEMU for the PCIe device and during the access of VA when > PTE access flags are updated. > > kvm_mmu_notifier_change_pte() --> kvm_set_spte_hve() --> kvm_set_spte_hva() --> clean_dcache_guest_page() > > The validation model doesn't have FWB capability supported. > __clean_dcache_guest_page() attempts to perform dcache flush on pcie bar address(not a valid_pfn()) through page_address(), > which doesn't have page table mapping and leads to exception. > > I have worked around the issue by filtering out the request if the pfn is not valid in __clean_dcache_guest_page(). > As the patch wasn't posted in the community, reverted it as well. Thank you Krishna for sharing the analysis. Best Regards, Sumit Gupta