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Tue, 6 May 2025 12:55:05 -0700 Date: Tue, 6 May 2025 12:55:02 -0700 From: Nicolin Chen To: Jason Gunthorpe CC: Alexey Kardashevskiy , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v2 06/19] iommufd/viommu: Add IOMMU_VIOMMU_SET/UNSET_VDEV_ID ioctl Message-ID: References: <6348cc7a72ce9f2ac0e9caf9737e70177a01eb74.1724776335.git.nicolinc@nvidia.com> <35701c5e-030a-4f52-b6f6-ed18368fb2cd@amd.com> <20241004114147.GF1365916@nvidia.com> <95ab62fa-bb1c-4e4a-a210-b0bdba0d4ad2@amd.com> <20250505170807.GP2260709@nvidia.com> <20250506125847.GA2260709@nvidia.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20250506125847.GA2260709@nvidia.com> X-NV-OnPremToCloud: AnonymousSubmission X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ5PEPF000001F5:EE_|SA1PR12MB7248:EE_ X-MS-Office365-Filtering-Correlation-Id: fb43138a-a590-47e3-49c8-08dd8cd7f27f X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|82310400026|376014|7416014|36860700013|1800799024; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 May 2025 19:55:26.9970 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: fb43138a-a590-47e3-49c8-08dd8cd7f27f 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: SJ5PEPF000001F5.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA1PR12MB7248 On Tue, May 06, 2025 at 09:58:47AM -0300, Jason Gunthorpe wrote: > On Mon, May 05, 2025 at 07:53:44PM -0700, Nicolin Chen wrote: > > On Mon, May 05, 2025 at 02:08:07PM -0300, Jason Gunthorpe wrote: > > > On Wed, Apr 30, 2025 at 12:58:47AM -0700, Nicolin Chen wrote: > > > The bus numbers can be reassigned at any time on the fly by the guest > > > by reprogramming the PCI hierarchy. > > > > Yes. If we take some aggressive use case into account, where its > > BDF number could change multiple times, I think it's natural for > > VMM to simply destroy the previous vDEVICE and allocate a new one > > with a new BDF number, right? > > We should not destroy the vdevice for something like that. In a CC > case that would unplug it from the VM which is not right. CC needs BDF to allocate a VDEV in the CC world. So, it cannot allocate a VDEV with BDF=0 firstly, which is what Alex reported. And even for a normal case that the device is migrating between PCI buses, CC might not be able to update the BDF (which can be a part of CC_VDEV_ALLOC instruction), even if iommufd supports an update ioctl. So, the underlying handler for an update ioctl is still to first destroy the VDEV and re-allocate a new one? Thanks Nicolin