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Fri, 15 Aug 2025 12:45:34 -0700 Date: Fri, 15 Aug 2025 12:45:33 -0700 From: Nicolin Chen To: "Tian, Kevin" CC: "robin.murphy@arm.com" , "joro@8bytes.org" , "bhelgaas@google.com" , "jgg@nvidia.com" , "will@kernel.org" , "robin.clark@oss.qualcomm.com" , "yong.wu@mediatek.com" , "matthias.bgg@gmail.com" , "angelogioacchino.delregno@collabora.com" , "thierry.reding@gmail.com" , "vdumpa@nvidia.com" , "jonathanh@nvidia.com" , "rafael@kernel.org" , "lenb@kernel.org" , "Liu, Yi L" , "baolu.lu@linux.intel.com" , "linux-arm-kernel@lists.infradead.org" , "iommu@lists.linux.dev" , "linux-kernel@vger.kernel.org" , "linux-arm-msm@vger.kernel.org" , "linux-mediatek@lists.infradead.org" , "linux-tegra@vger.kernel.org" , "linux-acpi@vger.kernel.org" , "linux-pci@vger.kernel.org" , "patches@lists.linux.dev" , "Jaroszynski, Piotr" , "Sethi, Vikram" , "helgaas@kernel.org" , "etzhao1900@gmail.com" Subject: Re: [PATCH v3 4/5] iommu: Introduce iommu_dev_reset_prepare() and iommu_dev_reset_done() Message-ID: References: <5ba556fc54777853c499186f494f3411d7a4a5a9.1754952762.git.nicolinc@nvidia.com> Precedence: bulk X-Mailing-List: linux-pci@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 Aug 2025 19:45:58.1715 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 619c9f34-117f-4fc2-6d4c-08dddc345b40 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.160];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: BL6PEPF0001AB51.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN2PR12MB4374 On Fri, Aug 15, 2025 at 09:14:28AM +0000, Tian, Kevin wrote: > > From: Nicolin Chen > > Sent: Tuesday, August 12, 2025 6:59 AM > > > [...] > > However, if there is a domain attachment/replacement happening during an > > ongoing reset, ATS routines may be re-activated between the two function > > calls. So, introduce a new pending_reset flag in group_device to defer an > > attachment during a reset, allowing iommu core to cache target domains in > > the SW level while bypassing the driver. The iommu_dev_reset_done() will > > re-attach these soft-attached domains, once the device reset is finished. > > attach could fail e.g. when device and domain are incompatible. This > deferred attach (until reset done) makes compatibility check impossible in > the resetting window, given the driver attach_dev callback is not called > in the normal attach path. > > Worse.. Ah, that's a good point! I missed that one.. > > + /* Shift RID domain back to group->domain */ > > + if (group->domain != group->blocking_domain) > > + WARN_ON(__iommu_attach_device(group->domain, dev)); > > ..means that an user could trigger WARN_ON() easily if he knows an attach > would fail. > > IMHO we may just fail attach request in the resetting window then > WARN_ON above makes sense as it's shifting back to a domain which was > originally attached to the resetting device. > > Not sure any valid case where one would want to attach/replace domain > for a resetting device... It would feel odd to me, if that could happen. So, failing it with -EBUSY sounds plausible to me. Thanks! Nicolin