From patchwork Wed Apr 26 15:03:21 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Yi Liu X-Patchwork-Id: 13224732 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id CCF51C7EE20 for ; Wed, 26 Apr 2023 15:05:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241501AbjDZPFI (ORCPT ); Wed, 26 Apr 2023 11:05:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58918 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241551AbjDZPEo (ORCPT ); Wed, 26 Apr 2023 11:04:44 -0400 Received: from mga03.intel.com (mga03.intel.com [134.134.136.65]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 23DDE76AD; Wed, 26 Apr 2023 08:04:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1682521477; x=1714057477; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=XTW5OvP/lz6wAuWYHWZPf0Ckv407oLnpgloaD6rISDo=; b=S8PGEmubWQLUgz37Qc/rq3yTYbbxYdI9z1ScAQQ4mhbudLM/guDPYCvP TbSFVnP4r8Z5OhWsuF/ZuzpsASPR/YrMfn2zHKGqbNloasAkfk5sJA3RO WR1CAPaO0AyDNK95NLV+0vG4UrAPc89gNcBXnbw76Wy7Pecbb2gyxkIKH kJsTAiIqMpL3Xh8Ezf9uj67dktLDNcOmQwd99G9rlIPdKUw66b2iAeIKV HTiEJb7ttkSQReIH4PdnxoDiAeouTflUWFOBBX5RrGSH/3GbJqkhKgTbY /cAKmfd/0z8ZGx/xrT6/jdS2ZCIEDqKUsHmCXUr/F+qSDDs/4xAgMeCCg A==; X-IronPort-AV: E=McAfee;i="6600,9927,10692"; a="349944718" X-IronPort-AV: E=Sophos;i="5.99,228,1677571200"; d="scan'208";a="349944718" Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 Apr 2023 08:04:04 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10692"; a="805544355" X-IronPort-AV: E=Sophos;i="5.99,228,1677571200"; d="scan'208";a="805544355" Received: from 984fee00a4c6.jf.intel.com ([10.165.58.231]) by fmsmga002.fm.intel.com with ESMTP; 26 Apr 2023 08:04:03 -0700 From: Yi Liu To: alex.williamson@redhat.com, jgg@nvidia.com, kevin.tian@intel.com Cc: joro@8bytes.org, robin.murphy@arm.com, cohuck@redhat.com, eric.auger@redhat.com, nicolinc@nvidia.com, kvm@vger.kernel.org, mjrosato@linux.ibm.com, chao.p.peng@linux.intel.com, yi.l.liu@intel.com, yi.y.sun@linux.intel.com, peterx@redhat.com, jasowang@redhat.com, shameerali.kolothum.thodi@huawei.com, lulu@redhat.com, suravee.suthikulpanit@amd.com, intel-gvt-dev@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, linux-s390@vger.kernel.org, xudong.hao@intel.com, yan.y.zhao@intel.com, terrence.xu@intel.com, yanting.jiang@intel.com, zhenzhong.duan@intel.com Subject: [PATCH v10 22/22] docs: vfio: Add vfio device cdev description Date: Wed, 26 Apr 2023 08:03:21 -0700 Message-Id: <20230426150321.454465-23-yi.l.liu@intel.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230426150321.454465-1-yi.l.liu@intel.com> References: <20230426150321.454465-1-yi.l.liu@intel.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org This gives notes for userspace applications on device cdev usage. Reviewed-by: Kevin Tian Signed-off-by: Yi Liu --- Documentation/driver-api/vfio.rst | 132 ++++++++++++++++++++++++++++++ 1 file changed, 132 insertions(+) diff --git a/Documentation/driver-api/vfio.rst b/Documentation/driver-api/vfio.rst index 363e12c90b87..4f21be7bda8a 100644 --- a/Documentation/driver-api/vfio.rst +++ b/Documentation/driver-api/vfio.rst @@ -239,6 +239,130 @@ group and can access them as follows:: /* Gratuitous device reset and go... */ ioctl(device, VFIO_DEVICE_RESET); +IOMMUFD and vfio_iommu_type1 +---------------------------- + +IOMMUFD is the new user API to manage I/O page tables from userspace. +It intends to be the portal of delivering advanced userspace DMA +features (nested translation [5], PASID [6], etc.) while also providing +a backwards compatibility interface for existing VFIO_TYPE1v2_IOMMU use +cases. Eventually the vfio_iommu_type1 driver, as well as the legacy +vfio container and group model is intended to be deprecated. + +The IOMMUFD backwards compatibility interface can be enabled two ways. +In the first method, the kernel can be configured with +CONFIG_IOMMUFD_VFIO_CONTAINER, in which case the IOMMUFD subsystem +transparently provides the entire infrastructure for the VFIO +container and IOMMU backend interfaces. The compatibility mode can +also be accessed if the VFIO container interface, ie. /dev/vfio/vfio is +simply symlink'd to /dev/iommu. Note that at the time of writing, the +compatibility mode is not entirely feature complete relative to +VFIO_TYPE1v2_IOMMU (ex. DMA mapping MMIO) and does not attempt to +provide compatibility to the VFIO_SPAPR_TCE_IOMMU interface. Therefore +it is not generally advisable at this time to switch from native VFIO +implementations to the IOMMUFD compatibility interfaces. + +Long term, VFIO users should migrate to device access through the cdev +interface described below, and native access through the IOMMUFD +provided interfaces. + +VFIO Device cdev +---------------- + +Traditionally user acquires a device fd via VFIO_GROUP_GET_DEVICE_FD +in a VFIO group. + +With CONFIG_VFIO_DEVICE_CDEV=y the user can now acquire a device fd +by directly opening a character device /dev/vfio/devices/vfioX where +"X" is the number allocated uniquely by VFIO for registered devices. +For noiommu devices, the character device would be named with "noiommu-" +prefix. e.g. /dev/vfio/devices/noiommu-vfioX. + +The cdev only works with IOMMUFD. Both VFIO drivers and applications +must adapt to the new cdev security model which requires using +VFIO_DEVICE_BIND_IOMMUFD to claim DMA ownership before starting to +actually use the device. Once BIND succeeds then a VFIO device can +be fully accessed by the user. + +VFIO device cdev doesn't rely on VFIO group/container/iommu drivers. +Hence those modules can be fully compiled out in an environment +where no legacy VFIO application exists. + +So far SPAPR does not support IOMMUFD yet. So it cannot support device +cdev neither. + +Device cdev Example +------------------- + +Assume user wants to access PCI device 0000:6a:01.0:: + + $ ls /sys/bus/pci/devices/0000:6a:01.0/vfio-dev/ + vfio0 + +This device is therefore represented as vfio0. The user can verify +its existence:: + + $ ls -l /dev/vfio/devices/vfio0 + crw------- 1 root root 511, 0 Feb 16 01:22 /dev/vfio/devices/vfio0 + $ cat /sys/bus/pci/devices/0000:6a:01.0/vfio-dev/vfio0/dev + 511:0 + $ ls -l /dev/char/511\:0 + lrwxrwxrwx 1 root root 21 Feb 16 01:22 /dev/char/511:0 -> ../vfio/devices/vfio0 + +Then provide the user with access to the device if unprivileged +operation is desired:: + + $ chown user:user /dev/vfio/devices/vfio0 + +Finally the user could get cdev fd by:: + + cdev_fd = open("/dev/vfio/devices/vfio0", O_RDWR); + +An opened cdev_fd doesn't give the user any permission of accessing +the device except binding the cdev_fd to an iommufd. After that point +then the device is fully accessible including attaching it to an +IOMMUFD IOAS/HWPT to enable userspace DMA:: + + struct vfio_device_bind_iommufd bind = { + .argsz = sizeof(bind), + .flags = 0, + }; + struct iommu_ioas_alloc alloc_data = { + .size = sizeof(alloc_data), + .flags = 0, + }; + struct vfio_device_attach_iommufd_pt attach_data = { + .argsz = sizeof(attach_data), + .flags = 0, + }; + struct iommu_ioas_map map = { + .size = sizeof(map), + .flags = IOMMU_IOAS_MAP_READABLE | + IOMMU_IOAS_MAP_WRITEABLE | + IOMMU_IOAS_MAP_FIXED_IOVA, + .__reserved = 0, + }; + + iommufd = open("/dev/iommu", O_RDWR); + + bind.iommufd = iommufd; // negative value means vfio-noiommu mode + ioctl(cdev_fd, VFIO_DEVICE_BIND_IOMMUFD, &bind); + + ioctl(iommufd, IOMMU_IOAS_ALLOC, &alloc_data); + attach_data.pt_id = alloc_data.out_ioas_id; + ioctl(cdev_fd, VFIO_DEVICE_ATTACH_IOMMUFD_PT, &attach_data); + + /* Allocate some space and setup a DMA mapping */ + map.user_va = (int64_t)mmap(0, 1024 * 1024, PROT_READ | PROT_WRITE, + MAP_PRIVATE | MAP_ANONYMOUS, 0, 0); + map.iova = 0; /* 1MB starting at 0x0 from device view */ + map.length = 1024 * 1024; + map.ioas_id = alloc_data.out_ioas_id;; + + ioctl(iommufd, IOMMU_IOAS_MAP, &map); + + /* Other device operations as stated in "VFIO Usage Example" */ + VFIO User API ------------------------------------------------------------------------------- @@ -566,3 +690,11 @@ This implementation has some specifics: \-0d.1 00:1e.0 PCI bridge: Intel Corporation 82801 PCI Bridge (rev 90) + +.. [5] Nested translation is an IOMMU feature which supports two stage + address translations. This improves the address translation efficiency + in IOMMU virtualization. + +.. [6] PASID stands for Process Address Space ID, introduced by PCI + Express. It is a prerequisite for Shared Virtual Addressing (SVA) + and Scalable I/O Virtualization (Scalable IOV).