{"id":2229147,"url":"http://patchwork.ozlabs.org/api/1.1/patches/2229147/?format=json","web_url":"http://patchwork.ozlabs.org/project/qemu-devel/patch/20260427181235.3003865-10-mhonap@nvidia.com/","project":{"id":14,"url":"http://patchwork.ozlabs.org/api/1.1/projects/14/?format=json","name":"QEMU Development","link_name":"qemu-devel","list_id":"qemu-devel.nongnu.org","list_email":"qemu-devel@nongnu.org","web_url":"","scm_url":"","webscm_url":""},"msgid":"<20260427181235.3003865-10-mhonap@nvidia.com>","date":"2026-04-27T18:12:35","name":"[RFC,9/9] vfio/listener: Skip DMA mapping for VFIO-owned RAM-device regions","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"b571d69b9a238dc0354a8f758cf2b01f367f6bfb","submitter":{"id":92895,"url":"http://patchwork.ozlabs.org/api/1.1/people/92895/?format=json","name":"Manish Honap","email":"mhonap@nvidia.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/qemu-devel/patch/20260427181235.3003865-10-mhonap@nvidia.com/mbox/","series":[{"id":501717,"url":"http://patchwork.ozlabs.org/api/1.1/series/501717/?format=json","web_url":"http://patchwork.ozlabs.org/project/qemu-devel/list/?series=501717","date":"2026-04-27T18:12:35","name":"QEMU: CXL Type-2 device passthrough via vfio-pci","version":1,"mbox":"http://patchwork.ozlabs.org/series/501717/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2229147/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2229147/checks/","tags":{},"headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=Nvidia.com header.i=@Nvidia.com header.a=rsa-sha256\n header.s=selector2 header.b=RNK4V1H2;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; 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Ip=[216.228.117.160];\n Helo=[mail.nvidia.com]","X-MS-Exchange-CrossTenant-AuthSource":"\n CY4PEPF0000EDD0.namprd03.prod.outlook.com","X-MS-Exchange-CrossTenant-AuthAs":"Anonymous","X-MS-Exchange-CrossTenant-FromEntityHeader":"HybridOnPrem","X-MS-Exchange-Transport-CrossTenantHeadersStamped":"BL3PR12MB6522","X-Spam_score_int":"-10","X-Spam_score":"-1.1","X-Spam_bar":"-","X-Spam_report":"(-1.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001,\n DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1,\n FORGED_SPF_HELO=1, SPF_HELO_PASS=-0.001,\n SPF_NONE=0.001 autolearn=no autolearn_force=no","X-Spam_action":"no action","X-Mailman-Approved-At":"Mon, 27 Apr 2026 15:57:41 -0400","X-BeenThere":"qemu-devel@nongnu.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"qemu development ","List-Unsubscribe":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Errors-To":"qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org","Sender":"qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org"},"content":"From: Manish Honap \n\nvfio_container_region_add() attempts an IOMMU DMA mapping for every\nRAM section that enters the guest address space. For VFIO mmap-backed\nregions (PCI BAR windows, CXL.mem regions), this mapping always fails:\nthe backing VMAs carry VM_IO | VM_PFNMAP flags and pin_user_pages()\nrefuses to pin VM_IO pages, so IOMMU_IOAS_MAP returns -EFAULT.\n\nCPU access to these regions goes through KVM Stage-2 page faults\nindependently of the SMMU/IOMMU, so no IOMMU entry is required for\ncorrect operation.\n\nAdd an early return for RAM-device sections owned by a VFIO device.\nvfio_get_vfio_device(memory_region_owner(section->mr)) returns non-NULL\nfor any mmap subregion created by vfio_region_mmap(), since\nmemory_region_init_ram_device_ptr() propagates the VFIOPCIDevice owner\nfrom the containing region. Matching on ownership covers both normal\nPCI BAR windows and CXL.mem regions uniformly; non-VFIO RAM-device\nregions such as NVDIMMs are unaffected and continue through the normal\nmapping path.\n\nSigned-off-by: Manish Honap \n---\n hw/vfio/listener.c | 14 ++++++++++++++\n 1 file changed, 14 insertions(+)","diff":"diff --git a/hw/vfio/listener.c b/hw/vfio/listener.c\nindex 31c3113f8f..46cad18357 100644\n--- a/hw/vfio/listener.c\n+++ b/hw/vfio/listener.c\n@@ -608,6 +608,20 @@ void vfio_container_region_add(VFIOContainer *bcontainer,\n pgmask + 1);\n return;\n }\n+\n+ /*\n+ * VFIO MMAP backed regions (CXL.mem) uses VM_IO | VM_PFNMAP VMAs\n+ * backed by physical device addresses. Skip vfio_container_dma_map\n+ * as mapping is not needed for this region.\n+ */\n+ if (vfio_get_vfio_device(memory_region_owner(section->mr))) {\n+ trace_vfio_listener_region_add_no_dma_map(\n+ memory_region_name(section->mr),\n+ section->offset_within_address_space,\n+ int128_getlo(section->size),\n+ pgmask + 1);\n+ return;\n+ }\n }\n \n ret = vfio_container_dma_map(bcontainer, iova, int128_get64(llsize),\n","prefixes":["RFC","9/9"]}