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CTRY:US; LANG:en; SCL:1; SRV:; IPV:NLI; SFV:NSPM; H:mail.nvidia.com; PTR:dc7edge2.nvidia.com; CAT:NONE; SFS:(13230040)(36860700013)(1800799024)(82310400026)(7416014)(376014); DIR:OUT; SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 16 Jun 2025 06:04:29.3479 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 11014934-04dc-4213-8487-08ddac9ba7ff X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a; Ip=[216.228.118.233]; Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: BL02EPF0001A0FF.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ2PR12MB8184 Received-SPF: permerror client-ip=2a01:111:f403:2418::62d; envelope-from=nicolinc@nvidia.com; helo=NAM12-BN8-obe.outbound.protection.outlook.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Thu, Jun 12, 2025 at 02:06:15PM +0000, Shameerali Kolothum Thodi wrote: > > >> The "switch" in vSMMU model is only needed by KVM for MSI doorbell > > >> translation. By thinking it carefully, maybe it shouldn't switch AS > > >> because VFIO might be confused if it somehow does get_address_space > > >> again in the future.. > > > > @Nicolin, not quite get the detailed logic for the MSI stuff on SMMU. But I > > agree with the last sentence. get_address_space should return a consistent > > AS. > > I think it is because, in ARM world the MSI doorbell address is translated by > an IOMMU. Hence, if the Guest device is behind IOMMU, it needs to return > the IOMMU AS in, > > kvm_irqchip_add_msi_route() > kvm_arch_fixup_msi_route() > pci_device_iommu_address_space() --> .get_address_space() -->At this point we now return IOMMU AS. > > If not the device will be configured with a wrong MSI doorbell address. Yes. The KVM code on ARM needs to translate the MSI location from gIOVA to gPA, because MSI on ARM is behind IOMMU. > Nicolin, you seems to suggest we could avoid this switching and always return > System AS. Does that mean we handle this KVM/MSI case separately? > Could you please detail out the idea? We could add one of following ops: get_msi_address_space get_msi_address/translate_msi_iova Thanks Nicolin