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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?LIq77WLTDKejBTSBM8JruOpDiTtL3x0iX+hmbDyxj5+vG4JTuKFpEXU9uuQ/?= =?us-ascii?Q?E5tLAmyXOFmSrujWhsNLLnG/c2JfKO/hiWfuWvjqGDuOZaT4gxsNiXgorNqo?= =?us-ascii?Q?n7tmJJJ93/dKWhmdJsNQwsfNVzgPz4t3KeV2cmqbjn/ZPGlawS+MPKH/Sx2O?= =?us-ascii?Q?esTLxsnqzeeOGaBLkFhdKAUSLM065dulPfcIF/z08zVpr1eWiKLdi+3Umg25?= =?us-ascii?Q?5krF+WhTYjQa0C2nC8k9ukQSsJm9LrTUBvzxsrMCsqRQ0n/qMDWN+4+pZTS6?= =?us-ascii?Q?00tHI8QVWRLUzuk2Uel6o7Dlaei14l/82UzjWTYibDmNhmYIkIxtP6a54Gtn?= =?us-ascii?Q?3Fqr6eeJzn7SwVr63EO1JVxDqnPPMuBDsGRn2Dui2Os/8fuUkEkMQ4pHNoWj?= =?us-ascii?Q?AO8OTfaTOv0rBuz7vC2OeXI7rMZyev2k5NZP9n7fjxA2hHMnun4lUFNh4/4e?= =?us-ascii?Q?+/1ycgVUBBO8oaOOYGYQ+6xw4s9leBlRlFygNPp01oxfZfcNc8Ni8sy0tJ3F?= =?us-ascii?Q?qqDCOkcT9qpPxH18TJRFNCpLY3/IhIgVxPSrCsQLJEHvE7fbg8I999ZVC6dX?= =?us-ascii?Q?5qD+nqWkOCIbridEnH8dknaJ6k+kVFRCaVPxugc0E8L/8Ddr/2m9rFqd8ozP?= =?us-ascii?Q?3Or+Q9FMq3aB1lsRciJQgRSo6ytBaFO5Jmcx7fE1+WvToiu78YmrKHIPDhze?= =?us-ascii?Q?ahvpEL/2ws5yJWIYJJbx1VH3jXk9GvAbaIxK5ywJ0H9G1tSHVJWNdMeHLp66?= =?us-ascii?Q?a6Asz3fIpEQMHIXPSYQMJtqb8zGzZou/LTYxYvET/SEYNsgbxFCQiVk5XZmG?= =?us-ascii?Q?xTdsZV07BNAwYfRPPoPvCya/NRp7TapXfnEv0gpbx0Flp1AFDS3TEUwdz/wz?= =?us-ascii?Q?i0QjbNapXz3iu6g5q5mee6gucp5ijYjM5vCw5C+qfoLZSfJ+F+OEUSLgBngV?= =?us-ascii?Q?N3qviL7JurA857rZDG12mT8ZL2f2gyCksAgxuxrs2jJopjMjoywqHgg/IXgx?= =?us-ascii?Q?W5goKNFKD/LHHdME+fiBZ/7z2FzvEpUcFVINJ1obO4iiojXT++QfE+0VLIMD?= =?us-ascii?Q?vxvz/7whOmu2oezXCqcP/gzs/6cn6HJ+qEjuBMMVpbK1glU3mSrNY+GfssyA?= =?us-ascii?Q?2/Jt5Tn4XhE3BZvdjfa83HwL3pTknJxdXwM9CLGbNL2/BQZSC+OubnmwoC6r?= =?us-ascii?Q?aqUQqrR4k398UYCfxZPeD7n7mucl8NFvP3sIZTlAlNPfs4RPwTZAQD5iU6o3?= =?us-ascii?Q?RfeGhOeN7rw3GaCcKUsELXNgcWXBhM0/iqYegdc73QxXKQGB8CrFudxiUPKD?= =?us-ascii?Q?b6CTKb0elMl2D/8kbP5akPCN?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 5c396d26-1071-4f7a-d451-08d92a7fd548 X-MS-Exchange-CrossTenant-AuthSource: BL0PR12MB5506.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 08 Jun 2021 13:17:57.9458 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: jGWGcN+qbdR/zkI8yO6tauZ6vweERBIJyNeRoXXVVoP3SKZjfAnSj/lhLmnmCS46 X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL1PR12MB5095 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 08, 2021 at 12:37:04PM +1000, David Gibson wrote: > > The PPC/SPAPR support allows KVM to associate a vfio group to an IOMMU > > page table so that it can handle iotlb programming from pre-registered > > memory without trapping out to userspace. > > To clarify that's a guest side logical vIOMMU page table which is > partially managed by KVM. This is an optimization - things can work > without it, but it means guest iomap/unmap becomes a hot path because > each map/unmap hypercall has to go > guest -> KVM -> qemu -> VFIO > > So there are multiple context transitions. Isn't this overhead true of many of the vIOMMUs? Can the fast path be generalized? Jason