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Thu, 15 May 2025 10:03:21 -0700 Date: Thu, 15 May 2025 10:03:20 -0700 From: Nicolin Chen To: "Tian, Kevin" CC: "jgg@nvidia.com" , "corbet@lwn.net" , "will@kernel.org" , "bagasdotme@gmail.com" , "robin.murphy@arm.com" , "joro@8bytes.org" , "thierry.reding@gmail.com" , "vdumpa@nvidia.com" , "jonathanh@nvidia.com" , "shuah@kernel.org" , "jsnitsel@redhat.com" , "nathan@kernel.org" , "peterz@infradead.org" , "Liu, Yi L" , "mshavit@google.com" , "praan@google.com" , "zhangzekun11@huawei.com" , "iommu@lists.linux.dev" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-tegra@vger.kernel.org" , "linux-kselftest@vger.kernel.org" , "patches@lists.linux.dev" , "mochs@nvidia.com" , "alok.a.tiwari@oracle.com" , "vasant.hegde@amd.com" Subject: Re: [PATCH v4 21/23] iommu/tegra241-cmdqv: Do not statically map LVCMDQs Message-ID: References: <80d41b740635b40dd0f9ed4279dc1cdeb3c8942c.1746757630.git.nicolinc@nvidia.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 15 May 2025 17:03:38.1605 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 25f31fd9-6b27-47a2-23a0-08dd93d26fb6 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.161];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: BL6PEPF00022572.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH8PR12MB6745 On Thu, May 15, 2025 at 08:20:44AM +0000, Tian, Kevin wrote: > > From: Nicolin Chen > > Sent: Friday, May 9, 2025 11:03 AM > > > > To simplify the mappings from global VCMDQs to VINTFs' LVCMDQs, the > > design > > chose to do static allocations and mappings in the global reset function. > > > > However, with the user-owned VINTF support, it exposes a security concern: > > if user space VM only wants one LVCMDQ for a VINTF, statically mapping two > > or more LVCMDQs creates a hidden VCMDQ that user space could DoS attack > > by > > writing random stuff to overwhelm the kernel with unhandleable IRQs. > > > > Thus, to support the user-owned VINTF feature, a LVCMDQ mapping has to > > be > > done dynamically. > > > > HW allows pre-assigning global VCMDQs in the CMDQ_ALLOC registers, > > without > > finalizing the mappings by keeping CMDQV_CMDQ_ALLOCATED=0. So, add a > > pair > > of map/unmap helper that simply sets/clears that bit. > > > > Delay the LVCMDQ mappings to tegra241_vintf_hw_init(), and the > > unmappings > > to tegra241_vintf_hw_deinit(). > > I don't know the specifics of tegra241-cmdqv. But the current description > is a bit misleading. for native tegra241_vintf_hw_init() is called from reset > so the mapping is still enabled in that path. for user-owned then > tegra241_vcmdq_map_lvcmdq() is called from tegra241_vintf_alloc_lvcmdq_user() > instead of tegra241_vintf_hw_init(). > > so nothing is actually delayed in this patch. It is delayed from tegra241_cmdqv_hw_reset() to later functions. The in-kernel VINTF0 is not literally delayed fundamentally as you mentioned because it needs to be allocated/mapped in probe(). The user-space VINTFs was previously allocated/mapped in probe(), now it's moved to user space handler, i.e. no mapping until user space asks for one. Perhaps I can make this "delay" statement more narrative for a clarification. Thanks Nicolin