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Mon, 27 Apr 2026 11:14:25 -0700 From: To: , , , , , , , , , , , , , , , , , , CC: , , , , , , , , , "Manish Honap" Subject: [RFC 9/9] vfio/listener: Skip DMA mapping for VFIO-owned RAM-device regions Date: Mon, 27 Apr 2026 23:42:35 +0530 Message-ID: <20260427181235.3003865-10-mhonap@nvidia.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20260427181235.3003865-1-mhonap@nvidia.com> References: <20260427181235.3003865-1-mhonap@nvidia.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: rnnvmail202.nvidia.com (10.129.68.7) To rnnvmail201.nvidia.com (10.129.68.8) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CY4PEPF0000EDD0:EE_|BL3PR12MB6522:EE_ X-MS-Office365-Filtering-Correlation-Id: 00024a03-dfee-4293-5e99-08dea488e204 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|82310400026|36860700016|376014|7416014|921020|56012099003|18002099003|22082099003; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: iJkJVTKPV21OueNuCeWULUALlNIcbEcEQSxGlRLVfaPS6+zSXVtp7vaktr9R0g3N5PJYCFDKiNUeu4SiVb05GpI3R5FdpGjCY6mrR11Sj/gQxoFNi/0BtSS8PfiY/nKE3JCMG5tMSJBc8Kd5CeaJby+DBu99cH3r99pI+0E8GZlorpLqpGs/cnTo26MfIem57vewvTA+BGuB4lqsobU3Q43atjh4gDCmMrp2QE66pF1CSozAtXE0vrfak9pBhnA8zH/N+9FHAx6R3UkIZj5s8LIWtoaO080Hv8UdiAyPuWbqlqSuUcKaWzXOzP2mebQ74md9zqS05OA6+2yTHFAOfvPq60IR+031ghl9fX5maXkE+FOKXdLqKEq2FDeBBVdFFUYiCvw7rcYnvmWFaZ3QI+uXORyNJ2UBxvZMT4zBw9/yf7jNI+GTp3c/b2BxKu9k X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 27 Apr 2026 18:14:54.6718 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 00024a03-dfee-4293-5e99-08dea488e204 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: CY4PEPF0000EDD0.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL3PR12MB6522 From: Manish Honap vfio_container_region_add() attempts an IOMMU DMA mapping for every RAM section that enters the guest address space. For VFIO mmap-backed regions (PCI BAR windows, CXL.mem regions), this mapping always fails: the backing VMAs carry VM_IO | VM_PFNMAP flags and pin_user_pages() refuses to pin VM_IO pages, so IOMMU_IOAS_MAP returns -EFAULT. CPU access to these regions goes through KVM Stage-2 page faults independently of the SMMU/IOMMU, so no IOMMU entry is required for correct operation. Add an early return for RAM-device sections owned by a VFIO device. vfio_get_vfio_device(memory_region_owner(section->mr)) returns non-NULL for any mmap subregion created by vfio_region_mmap(), since memory_region_init_ram_device_ptr() propagates the VFIOPCIDevice owner from the containing region. Matching on ownership covers both normal PCI BAR windows and CXL.mem regions uniformly; non-VFIO RAM-device regions such as NVDIMMs are unaffected and continue through the normal mapping path. Signed-off-by: Manish Honap --- hw/vfio/listener.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/hw/vfio/listener.c b/hw/vfio/listener.c index 31c3113f8f..46cad18357 100644 --- a/hw/vfio/listener.c +++ b/hw/vfio/listener.c @@ -608,6 +608,20 @@ void vfio_container_region_add(VFIOContainer *bcontainer, pgmask + 1); return; } + + /* + * VFIO MMAP backed regions (CXL.mem) uses VM_IO | VM_PFNMAP VMAs + * backed by physical device addresses. Skip vfio_container_dma_map + * as mapping is not needed for this region. + */ + if (vfio_get_vfio_device(memory_region_owner(section->mr))) { + trace_vfio_listener_region_add_no_dma_map( + memory_region_name(section->mr), + section->offset_within_address_space, + int128_getlo(section->size), + pgmask + 1); + return; + } } ret = vfio_container_dma_map(bcontainer, iova, int128_get64(llsize), -- 2.25.1