From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 99447CD4F54 for ; Wed, 27 May 2026 10:23:58 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id C55A410E768; Wed, 27 May 2026 10:23:57 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=meta.com header.i=@meta.com header.b="TvqXTS+v"; dkim-atps=neutral Received: from mx0b-00082601.pphosted.com (mx0b-00082601.pphosted.com [67.231.153.30]) by gabe.freedesktop.org (Postfix) with ESMTPS id E271310E259 for ; Wed, 27 May 2026 10:23:44 +0000 (UTC) Received: from pps.filterd (m0528006.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id 64R6Idck2507771; Wed, 27 May 2026 03:23:29 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=meta.com; h=cc :content-transfer-encoding:content-type:date:from:message-id :mime-version:subject:to; s=s2048-2025-q2; bh=BuInzWm6zlnr40MeLG Xyu48AjR8YXaNjRNA9wv7wh9s=; b=TvqXTS+vDPs+whi8CfXfKby7Bvox8F/qZO oEz0bfZ+PeiBpu1wgSfnrHT+hOhVNUbMFqSd3Xwy1NXQvOWxMecZh3YT8JegzQ01 5H2kMisJBBrAit30l8Vj4RGnMjOETK9sXCKsuOsVag7/uYs3QS15ZK22nWbNGDH+ fdiZqFoHeEU6ZU2tmShL+9Pwbi/A9Rnt/U0rqAWbKzvgCh+DpZC8JFrTnHWaMn86 ODeKylxt9h/KYANsBd5aYikzQsr6AbxixBCKgGbisWN7VPKVc5ZPg0cZVitAG9PH UH+PcuVF7yD7S1VbU/+0ILe3PNLNa5UYi3gFtGrK0wl0qf7MJstA== Received: from mail.thefacebook.com ([163.114.134.16]) by mx0a-00082601.pphosted.com (PPS) with ESMTPS id 4edpnga485-3 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT); Wed, 27 May 2026 03:23:28 -0700 (PDT) Received: from localhost (2620:10d:c085:108::4) by mail.thefacebook.com (2620:10d:c08b:78::c78f) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.2.2562.41; Wed, 27 May 2026 10:23:26 +0000 From: Matt Evans To: Alex Williamson , Leon Romanovsky , Jason Gunthorpe , Alex Mastro , =?UTF-8?q?Christian=20K=C3=B6nig?= , Bjorn Helgaas , Logan Gunthorpe CC: Mahmoud Adam , David Matlack , =?UTF-8?q?Bj=C3=B6rn=20T=C3=B6pel?= , Sumit Semwal , Kevin Tian , Ankit Agrawal , Pranjal Shrivastava , Alistair Popple , Vivek Kasireddy , , , , , , Subject: [PATCH v2 0/9] vfio/pci: Add mmap() for DMABUFs Date: Wed, 27 May 2026 03:23:03 -0700 Message-ID: <20260527102319.100128-1-mattev@meta.com> X-Mailer: git-send-email 2.52.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-Originating-IP: [2620:10d:c085:108::4] X-Proofpoint-GUID: pDX_pw9F0mPlau3NKH58yeq_Xy9cVwzx X-Authority-Analysis: v=2.4 cv=PME/P/qC c=1 sm=1 tr=0 ts=6a16c621 cx=c_pps a=CB4LiSf2rd0gKozIdrpkBw==:117 a=CB4LiSf2rd0gKozIdrpkBw==:17 a=NGcC8JguVDcA:10 a=VkNPw1HP01LnGYTKEx00:22 a=7x6HtfJdh03M6CCDgxCd:22 a=kkcUborcUVj0H7zxAXTl:22 a=VwQbUJbxAAAA:8 a=FOH2dFAWAAAA:8 a=VabnemYjAAAA:8 a=NEAV23lmAAAA:8 a=h-ECioDzeyvzXXNZi24A:9 a=gKebqoRLp9LExxC7YDUY:22 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTI3MDEwMCBTYWx0ZWRfX9GH/QGKNIhYF k2y0OfCPd9PjHLger9H36g3A9qaPKmoXqLJS4EIXPcBEJiVebQppGgReFNWjFGZIVH21Nyuz3cv 7KjY1OJjdeY6vvpfyYEBmiuszRSR9bhsv6M71gFLqoPjqo9VqzyXTufRh0VwKB4lCp/RSzDuocT Yk5pPd2TGUIXu9QicQH7tFUiPS1xEanT/Bg1L3EYni8DRXocrbKCEeTqDcGHsaKF2Dvp23ly3S0 TlEKPk4Qt7UxriYRPbidPLweC0wKyudnp6LYkm0l88sEG8AUu2cEVWwbQ7i29lj1zb6hujD/4to j66ygBFWps4NJjADdssdUVb4idNEM2deJ+TRtsmB2K3AsQShMwYWfaJjthq7QL8bNT/AGuxTfTu ord+iJ40c5zvNAVPrmCfDnGKh1lJjkX3xon7V1mhYFo6LeFbmZUxRp1yj3Fz94jpB/UiMN7760I tEp89peWJ13UhgvQ+uw== X-Proofpoint-ORIG-GUID: pDX_pw9F0mPlau3NKH58yeq_Xy9cVwzx X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.125,FMLib:17.12.100.49 definitions=2026-05-27_01,2026-05-26_03,2025-10-01_01 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Hi all, This series is based on previous RFCs/discussions: Tech topic: https://lore.kernel.org/linux-iommu/20250918214425.2677057-1-amastro@fb.com/ RFCv1: https://lore.kernel.org/all/20260226202211.929005-1-mattev@meta.com/ RFCv2: https://lore.kernel.org/kvm/20260312184613.3710705-1-mattev@meta.com/ The background/rationale is covered in more detail in the RFC cover letters. The TL;DR is: The goal is to enable userspace driver designs that use VFIO to export DMABUFs representing subsets of PCI device BARs, and "vend" those buffers from a primary process to other subordinate processes by fd. These processes then mmap() the buffers and their access to the device is isolated to the exported ranges. This is an improvement on sharing the VFIO device fd to subordinate processes, which would allow unfettered access. This is achieved by enabling mmap() of vfio-pci DMABUFs, passed by fd to subordinate processes. Second, a new ioctl()-based revocation mechanism is added to allow the primary process to forcibly revoke access to previously-shared BAR spans, even if the subordinate processes haven't cleanly exited. (The related topic of safe delegation of iommufd control to the subordinate processes is not addressed here, and is follow-up work.) As well as isolation and revocation, another advantage to accessing a BAR through a VMA backed by a DMABUF is that it's straightforward to mmap() the buffer with access attributes, such as write-combining. Feedback from the RFCs requested that, instead of creating DMABUF-specific vm_ops and .fault paths, to go the whole way and migrate the existing VFIO PCI BAR mmap() to be backed by a DMABUF too, resulting in a common vm_ops and fault handler for mmap()s of both the VFIO device and explicitly-exported DMABUFs. This will help future iommufd emulation of VFIO Type1 peer-to-peer, making it easier to get a DMABUF for a VFIO BAR as a DMA target. mmap() conversion to use DMABUF underneath has been done for vfio-pci, but not sub-drivers: nvgrace-gpu's mmap() override path is unchanged; I kept this out of scope for now not least because I don't have a thorough test setup for this system. I would prefer to help the nvgrace-gpu maintainers enable BAR mmap() DMABUFs themselves. Notes on patches ================ PCI/P2PDMA: Add CONFIG_PCI_P2PDMA_CORE Later in the series, vfio-pci's mmap() is going to depend on pcim_p2pdma_provider() which depended on CONFIG_PCI_P2PDMA, which in turn depended on ZONE_DEVICE (which isn't available on 32-bit and some archs, because they lack MEMORY_HOTPLUG and friends). VFIO does _not_ require actual P2P to be present for basic mmap() functionality, only for the optional CONFIG_DMA_SHARED_BUFFER feature. This splits P2PDMA into a CONFIG_PCI_P2PDMA_CORE (which currently contains pcim_p2pdma_provider()) and an optional CONFIG_PCI_P2PDMA (which depends on ZONE_DEVICE etc., and provides P2P functionality). vfio/pci: Add a helper to look up PFNs for DMABUFs vfio/pci: Add a helper to create a DMABUF for a BAR-map VMA The first is for a DMABUF VMA fault handler to determine arbitrary-sized PFNs from ranges in DMABUF. Secondly, refactor DMABUF export for use by the existing export feature and add a new helper that creates a DMABUF corresponding to a VFIO BAR mmap() request. vfio/pci: Convert BAR mmap() to use a DMABUF The vfio-pci core mmap() creates a DMABUF with the helper, and the vm_ops fault handler uses the other helper to resolve the fault. Because this depends on DMABUF structs/code, CONFIG_VFIO_PCI_CORE needs to depend on CONFIG_DMA_SHARED_BUFFER. The CONFIG_VFIO_PCI_DMABUF still conditionally enables the export support code. NOTE: The user mmap()s a device fd, but the resulting VMA's vm_file becomes that of the DMABUF which takes ownership of the device and puts it on release. This maintains the existing behaviour of a VMA keeping the VFIO device open. BAR zapping then happens via the existing vfio_pci_dma_buf_move() path, which now needs to unmap PTEs in the DMABUF's address_space. vfio/pci: Provide a user-facing name for BAR mappings There was a request for decent debug naming in /proc//maps etc. comparable to the existing VFIO names: since the VMAs are DMABUFs, they have a "dmabuf:" prefix and can't be 100% identical to before. This is a user-visible change, but this patch at least now gives us extra info on the BDF & BAR being mapped. vfio/pci: Clean up BAR zap and revocation In general (see NOTE!) the vfio_pci_zap_bars() is now obsolete, since it unmaps PTEs in the VFIO device address_space which is now unused. This consolidates all calls (e.g. around reset) with the neighbouring vfio_pci_dma_buf_move()s into new functions, to revoke-zap/unrevoke. !!! NOTE: the nvgrace-gpu driver continues to use its own private vm_ops, fault handler, etc. for its special memregions, and these DO still add PTEs to the VFIO device address_space. So, a temporary flag, vdev->bar_needs_zap, maintains the old behaviour for this use. At least this patch's consolidation makes it easy to remove the remaining zap when this need goes away; a FIXME reminds that this can be removed when nvgrace-gpu is converted. vfio/pci: Support mmap() of a VFIO DMABUF Adds mmap() for a DMABUF fd exported from vfio-pci. It was a goal to keep the VFIO device fd lifetime behaviour unchanged with respect to the DMABUFs. An application can close all device fds, and this will revoke/clean up all DMABUFs; no mappings or other access can be performed now. When enabling mmap() of the DMABUFs, this means access through the VMA is also revoked. This complicates the fault handler because whilst the DMABUF exists, it has no guarantee that the corresponding VFIO device is still alive. Adds synchronisation ensuring the vdev is available before vdev->memory_lock is touched; this holds the device registration so that even if the buffer has been cleaned up, vdev hasn't been freed and so the lock can be safely taken. (I decided against the alternative of preventing cleanup by holding the VFIO device open if any DMABUFs exist, because it's both a change of behaviour and less clean overall.) I've added a chonky comment in place, happy to clarify more if you have ideas. This commit makes VFIO_PCI_CORE depend on PCI_P2PDMA_CORE (commit 1) to bring in (only) the P2PDMA provider code. vfio/pci: Permanently revoke a DMABUF on request By weight, this is mostly a rename of revoked to an enum, status. There are now 3 states for a buffer, usable and revoked temporary/permanent. A new VFIO device ioctl is added, VFIO_DEVICE_PCI_DMABUF_REVOKE, which passes a DMABUF (exported from that device) and permanently revokes it. Thus a userspace driver can guarantee any downstream consumers of a shared fd are prevented from accessing a BAR range, and that range can be reused. The code doing revocation in vfio_pci_dma_buf_move() is moved, unchanged, to a common function for use by _move() and the new ioctl path. Q: I can't think of a good reason to temporarily revoke/unrevoke buffers from userspace, so didn't add a 'flags' field to the ioctl struct. Easy to add if people think it's worthwhile for future use. vfio/pci: Add mmap() attributes to DMABUF feature Adds a new VFIO feature, VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR. After a DMABUF is exported, this feature ioctl() isused to set a memory attribute that will be used by future mmap()s of the DMABUF fd (i.e. it does nothing for any existing maps). The default is UC, and via the feature one can specify CPU access as WC. The attribute is an enum/scalar rather than bitmap/cumulative. The attributes follow a "try-fail" model where a client can request an attribute and either succeed or fail with ENOTSUPP if it's unknown; if future attributes are platform-specific then their support can be probed. (Since it's just UC/WC for now, there is no reservation or numeric structure to the namespace yet, but we could support system/arch-specific values in future by carving out base + arch-specific + IMPDEF ranges.) Testing ======= (The [RFC ONLY] userspace test program, for QEMU edu-plus, has been dropped from the series, but can be found in the GitHub branch below. It at least illustrates the export, map, revoke, attribute, and close semantics interoperate.) This code has been tested in mapping DMABUFs of single/multiple ranges, aliasing mmap()s, aliasing ranges across DMABUFs, vm_pgoff > 0, revocation, shutdown/cleanup scenarios, and hugepage mappings seem to work correctly. I've lightly tested WC mappings also (by observing resulting PTEs as having the correct attributes...). No regressions observed on the VFIO selftests, or on our internal vfio-pci applications. End === This is based on VFIO next (e.g. at b9285405c5f6). These commits are on GitHub for easier browsing, along with "[RFC ONLY] selftests: vfio: Add standalone vfio_dmabuf_mmap_test": https://github.com/metamev/linux/compare/b9285405c5f6...metamev:linux:dev/mev/vfio-dmabuf-mmap-v2 Thanks for reading, Matt ================================================================================ Change log: v2: - Rebase on VFIO next, picking up Alex's vfio_pci_dma_buf_move()/vfio_pci_dma_buf_cleanup() fixes, and dropping "vfio/pci: Fix vfio_pci_dma_buf_cleanup() double-put" - Added "PCI/P2PDMA: Add CONFIG_PCI_P2PDMA_CORE" so that the newly-added vfio-pci hard dependency on the P2PDMA provider instead pulls in the _CORE variant and not the full-fat CONFIG_PCI_P2PDMA. This means that the core of vfio-pci does not need ZONE_DEVICE, but if it's available then enabling P2PDMA in turn enables DMABUF export. Fixes basic VFIO operation on 32b or other platforms without ZONE_DEVICE. - Fixed comment inaccuracy in vfio_pci_dma_buf_revoke() and cleaned up vdev validity test. - vfio_pci_dma_buf_find_pfn(): use PAGE_ALIGN(), better span variable naming, OVF check - Made vm_pgoffs use consistent (keeping the resource index at the top and masking where offset is used). For BAR mmap, use new vma_pgoff_adjust to create the DMABUF with the exact mmap()ed span instead of from the start of the BAR with an invisible portion before the mapping. - Added VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR to set memory attributes, instead of using the export `flags` field. - vfio_pci_ioctl_reset: Moved vfio_pci_zap_revoke_bars() (effectively, vfio_pci_dma_buf_move()) back after D0 transition. Note, if a BAR zap is needed, it's done in this function so now happens after this D0 transition with the _move; it was done before it at the time of the memory_lock taking. - Minimised vfio_pci_dma_buf_mmap() (removed redundant span check), added READ_ONCE for memattr - Misc fixes: comment in DMABUF name generation, removed superfluous READ_ONCE from faulthandler v1: https://lore.kernel.org/kvm/20260416131815.2729131-1-mattev@meta.com/ - Cleanup of the common DMABUF-aware VMA vm_ops fault handler and export code. - Fixed a lot of races, particularly faults racing with DMABUF cleanup (if the VFIO device fds close, for example). - Added nicer human-readable names for VFIO mmap() VMAs RFCv2: Respin based on the feedback/suggestions: https://lore.kernel.org/kvm/20260312184613.3710705-1-mattev@meta.com/ - Transform the existing VFIO BAR mmap path to also use DMABUFs behind the scenes, and then simply share that code for explicitly-mapped DMABUFs. Jason wanted to go that direction to enable iommufd VFIO type 1 emulation to pick up a DMABUF for an IO mapping. - Revoke buffers using a VFIO device fd ioctl RFCv1: https://lore.kernel.org/all/20260226202211.929005-1-mattev@meta.com/ Matt Evans (9): PCI/P2PDMA: Add CONFIG_PCI_P2PDMA_CORE vfio/pci: Add a helper to look up PFNs for DMABUFs vfio/pci: Add a helper to create a DMABUF for a BAR-map VMA vfio/pci: Convert BAR mmap() to use a DMABUF vfio/pci: Provide a user-facing name for BAR mappings vfio/pci: Clean up BAR zap and revocation vfio/pci: Support mmap() of a VFIO DMABUF vfio/pci: Permanently revoke a DMABUF on request vfio/pci: Add mmap() attributes to DMABUF feature drivers/pci/Kconfig | 10 +- drivers/pci/Makefile | 2 +- drivers/pci/p2pdma.c | 16 + drivers/vfio/pci/Kconfig | 4 +- drivers/vfio/pci/Makefile | 3 +- drivers/vfio/pci/nvgrace-gpu/main.c | 5 + drivers/vfio/pci/vfio_pci_config.c | 30 +- drivers/vfio/pci/vfio_pci_core.c | 225 +++++++++--- drivers/vfio/pci/vfio_pci_dmabuf.c | 548 ++++++++++++++++++++++++---- drivers/vfio/pci/vfio_pci_priv.h | 57 ++- include/linux/pci-p2pdma.h | 24 +- include/linux/pci.h | 2 +- include/linux/vfio_pci_core.h | 1 + include/uapi/linux/vfio.h | 57 +++ 14 files changed, 815 insertions(+), 169 deletions(-) -- 2.47.3