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McKenney" , Pawan Gupta , "Peter Zijlstra (Intel)" , Pranjal Shrivastava , Pratyush Yadav , Raghavendra Rao Ananta , Randy Dunlap , Rodrigo Vivi , Saeed Mahameed , Samiullah Khawaja , Shuah Khan , Vipin Sharma , Vivek Kasireddy , William Tu , Yi Liu , Zhu Yanjun Subject: Re: [PATCH v3 07/24] vfio/pci: Preserve vfio-pci device files across Live Update Message-ID: <20260421184433.GG3199414@nvidia.com> References: <20260323235817.1960573-1-dmatlack@google.com> <20260323235817.1960573-8-dmatlack@google.com> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-ClientProxiedBy: BL1PR13CA0424.namprd13.prod.outlook.com (2603:10b6:208:2c3::9) To LV8PR12MB9620.namprd12.prod.outlook.com (2603:10b6:408:2a1::19) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: LV8PR12MB9620:EE_|DS7PR12MB8322:EE_ X-MS-Office365-Filtering-Correlation-Id: 11e3a8bb-3d72-426d-1df7-08de9fd60883 X-LD-Processed: 43083d15-7273-40c1-b7db-39efd9ccc17a,ExtAddr X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|7416014|376014|1800799024|18002099003|56012099003|22082099003; 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> > + struct vfio_pci_core_device *vdev; > > + struct pci_dev *pdev; > > + int ret; > > + > > + vdev = container_of(device, struct vfio_pci_core_device, vdev); > > + pdev = vdev->pdev; > > + > > + guard(mutex)(&device->dev_set->lock); > > + > > + /* > > + * Userspace must disable interrupts on the device prior to freeze so > > + * that the device does not send any interrupts until new interrupt > > + * handlers have been established by the next kernel. > > + */ > > + if (vdev->irq_type != VFIO_PCI_NUM_IRQS) { > > + pci_err(pdev, "Freeze failed! Interrupts are still enabled.\n"); > > + return -EINVAL; > > + } > > + > > + ret = pci_load_saved_state(pdev, vdev->pci_saved_state); > > + if (ret) > > + return ret; > > + > > + vfio_pci_core_try_reset(vdev); > > I think a call to pci_clear_master() is needed here to so the device > stops issuing memory transactions while VFIO is trying to resetting > it. That doesn't sound right, reset should always work.. Didn't look beyond this hunk but why is a function called 'freeze' donig a reset anyhow? > Sashiko also wondered if pci_clear_master() is needed to ensure that > the device has bus mastering disabled during the kexec Only devices that are not being preserved.. > think that is actually an issue. vfio_pci_core_enable() makes sure > that vdev->pci_saved_state has bus mastering disabled, so > pci_restore_state() below here should guaranteed it is clear during > kexec. .. and bus mastering should not be disabled on any device expecting to be preserved .. Jason