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 X-Spam-Level: X-Spam-Status: No, score=-16.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B131FC433EA for ; Wed, 31 Mar 2021 08:07:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8E160619EF for ; Wed, 31 Mar 2021 08:07:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234430AbhCaIH2 (ORCPT ); Wed, 31 Mar 2021 04:07:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47528 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234354AbhCaIG4 (ORCPT ); Wed, 31 Mar 2021 04:06:56 -0400 Received: from mail-pj1-x102f.google.com (mail-pj1-x102f.google.com [IPv6:2607:f8b0:4864:20::102f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BC269C061574 for ; Wed, 31 Mar 2021 01:06:56 -0700 (PDT) Received: by mail-pj1-x102f.google.com with SMTP id lr1-20020a17090b4b81b02900ea0a3f38c1so2627709pjb.0 for ; Wed, 31 Mar 2021 01:06:56 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20150623.gappssmtp.com; s=20150623; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=DrGe+wSNv+5GrL/VvyrIF4G5z2Kf+xg5gmEDQCgKf7s=; b=DqzZ8q+OkgiXiUnK9PFEYEY4GPyyJUNJwl9trmeo91/ckMTVGZku5qS+JYUp6zbltv 7JvdkVX4/kn4rtl7cFCIfEfQP+rRDpBLK3lx/1fTetBxfqIxNrXCCGHQhn3Cs9UAAe8j dEfKQZNP/uRhRK/+NsTGf2ALmlqAwKGqnklVdGVTMTTpLvLxqs+ujglBcrnEeLW9F8st IYRilOFnC/ht3Qb86fq7BfeHYXVqAkQTbbVeDhg84tYsOWIxpLX+liISgJbcKto8LEu7 bc1z4i3IgIPP24H5wRqaa2c6qh0L8tCPEDgWo7QOxQQdgBRuH6lxgUd+3n+ii0sHchYm WAxA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=DrGe+wSNv+5GrL/VvyrIF4G5z2Kf+xg5gmEDQCgKf7s=; b=FvgjWbl3+TM2xXGe+kXsvhrH2aybPMfSPwLn5NAq0Za6GRz4B7VAQn2OIEPlSbqbJA i4EGt4lEOkE+Jl2fY7Azy2pFFbqWcqqqs9p3RltKxB/cdVT9XIyiyirHvipfTGlIkk7R QLITgrP4c8gn539kTpEEmVCAXbwBiVAd3NtLb8RY9vip5bE3s34nL6Wfd/r8iaamBD9v xcvxMkJFFRTimBr4DdQ86RUorvAy/9RHuK9mqo1A9pmg4iDF6V9UK8ROtdg+F+S34+Fm Opxkiz5hPkE4qh2Y384dH7GKdgJw/aR3cWQRHVY6DnwgH42aycNdopwYSfu7EKDGhCfg EDGw== X-Gm-Message-State: AOAM533P9r/EgQQyUHpb55dbgK37YcSy8g74JqHVyfrVSTZ4FP3otmJT RathhUwNpp5M6l5ZBCGWVyOR X-Google-Smtp-Source: ABdhPJzUZ0iCW38qBzP+z9ejwSF3QR26iU/iND3BjH9uOIBsmROmq3cVYSj9jxodUlUSY5l5upx6Gg== X-Received: by 2002:a17:90b:3551:: with SMTP id lt17mr2338546pjb.89.1617178016286; Wed, 31 Mar 2021 01:06:56 -0700 (PDT) Received: from localhost ([139.177.225.243]) by smtp.gmail.com with ESMTPSA id w79sm1324798pfc.87.2021.03.31.01.06.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 31 Mar 2021 01:06:55 -0700 (PDT) From: Xie Yongji To: mst@redhat.com, jasowang@redhat.com, stefanha@redhat.com, sgarzare@redhat.com, parav@nvidia.com, hch@infradead.org, christian.brauner@canonical.com, rdunlap@infradead.org, willy@infradead.org, viro@zeniv.linux.org.uk, axboe@kernel.dk, bcrl@kvack.org, corbet@lwn.net, mika.penttila@nextfour.com, dan.carpenter@oracle.com Cc: virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, kvm@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: [PATCH v6 10/10] Documentation: Add documentation for VDUSE Date: Wed, 31 Mar 2021 16:05:19 +0800 Message-Id: <20210331080519.172-11-xieyongji@bytedance.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210331080519.172-1-xieyongji@bytedance.com> References: <20210331080519.172-1-xieyongji@bytedance.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org VDUSE (vDPA Device in Userspace) is a framework to support implementing software-emulated vDPA devices in userspace. This document is intended to clarify the VDUSE design and usage. Signed-off-by: Xie Yongji --- Documentation/userspace-api/index.rst | 1 + Documentation/userspace-api/vduse.rst | 212 ++++++++++++++++++++++++++++++++++ 2 files changed, 213 insertions(+) create mode 100644 Documentation/userspace-api/vduse.rst diff --git a/Documentation/userspace-api/index.rst b/Documentation/userspace-api/index.rst index acd2cc2a538d..f63119130898 100644 --- a/Documentation/userspace-api/index.rst +++ b/Documentation/userspace-api/index.rst @@ -24,6 +24,7 @@ place where this information is gathered. ioctl/index iommu media/index + vduse .. only:: subproject and html diff --git a/Documentation/userspace-api/vduse.rst b/Documentation/userspace-api/vduse.rst new file mode 100644 index 000000000000..8c4e2b2df8bb --- /dev/null +++ b/Documentation/userspace-api/vduse.rst @@ -0,0 +1,212 @@ +================================== +VDUSE - "vDPA Device in Userspace" +================================== + +vDPA (virtio data path acceleration) device is a device that uses a +datapath which complies with the virtio specifications with vendor +specific control path. vDPA devices can be both physically located on +the hardware or emulated by software. VDUSE is a framework that makes it +possible to implement software-emulated vDPA devices in userspace. + +How VDUSE works +------------ +Each userspace vDPA device is created by the VDUSE_CREATE_DEV ioctl on +the character device (/dev/vduse/control). Then a device file with the +specified name (/dev/vduse/$NAME) will appear, which can be used to +implement the userspace vDPA device's control path and data path. + +To implement control path, a message-based communication protocol and some +types of control messages are introduced in the VDUSE framework: + +- VDUSE_SET_VQ_ADDR: Set the vring address of virtqueue. + +- VDUSE_SET_VQ_NUM: Set the size of virtqueue + +- VDUSE_SET_VQ_READY: Set ready status of virtqueue + +- VDUSE_GET_VQ_READY: Get ready status of virtqueue + +- VDUSE_SET_VQ_STATE: Set the state for virtqueue + +- VDUSE_GET_VQ_STATE: Get the state for virtqueue + +- VDUSE_SET_FEATURES: Set virtio features supported by the driver + +- VDUSE_GET_FEATURES: Get virtio features supported by the device + +- VDUSE_SET_STATUS: Set the device status + +- VDUSE_GET_STATUS: Get the device status + +- VDUSE_SET_CONFIG: Write to device specific configuration space + +- VDUSE_GET_CONFIG: Read from device specific configuration space + +- VDUSE_UPDATE_IOTLB: Notify userspace to update the memory mapping in device IOTLB + +Those control messages are mostly based on the vdpa_config_ops in +include/linux/vdpa.h which defines a unified interface to control +different types of vdpa device. Userspace needs to read()/write() +on the VDUSE device file to receive/reply those control messages +from/to VDUSE kernel module as follows: + +.. code-block:: c + + static int vduse_message_handler(int dev_fd) + { + int len; + struct vduse_dev_request req; + struct vduse_dev_response resp; + + len = read(dev_fd, &req, sizeof(req)); + if (len != sizeof(req)) + return -1; + + resp.request_id = req.request_id; + + switch (req.type) { + + /* handle different types of message */ + + } + + len = write(dev_fd, &resp, sizeof(resp)); + if (len != sizeof(resp)) + return -1; + + return 0; + } + +In the data path, vDPA device's iova regions will be mapped into userspace +with the help of VDUSE_IOTLB_GET_FD ioctl on the VDUSE device file: + +- VDUSE_IOTLB_GET_FD: get the file descriptor to the first overlapped iova region. + Userspace can access this iova region by passing fd and corresponding size, offset, + perm to mmap(). For example: + +.. code-block:: c + + static int perm_to_prot(uint8_t perm) + { + int prot = 0; + + switch (perm) { + case VDUSE_ACCESS_WO: + prot |= PROT_WRITE; + break; + case VDUSE_ACCESS_RO: + prot |= PROT_READ; + break; + case VDUSE_ACCESS_RW: + prot |= PROT_READ | PROT_WRITE; + break; + } + + return prot; + } + + static void *iova_to_va(int dev_fd, uint64_t iova, uint64_t *len) + { + int fd; + void *addr; + size_t size; + struct vduse_iotlb_entry entry; + + entry.start = iova; + entry.last = iova + 1; + fd = ioctl(dev_fd, VDUSE_IOTLB_GET_FD, &entry); + if (fd < 0) + return NULL; + + size = entry.last - entry.start + 1; + *len = entry.last - iova + 1; + addr = mmap(0, size, perm_to_prot(entry.perm), MAP_SHARED, + fd, entry.offset); + close(fd); + if (addr == MAP_FAILED) + return NULL; + + /* do something to cache this iova region */ + + return addr + iova - entry.start; + } + +Besides, the following ioctls on the VDUSE device file are provided to support +interrupt injection and setting up eventfd for virtqueue kicks: + +- VDUSE_VQ_SETUP_KICKFD: set the kickfd for virtqueue, this eventfd is used + by VDUSE kernel module to notify userspace to consume the vring. + +- VDUSE_INJECT_VQ_IRQ: inject an interrupt for specific virtqueue + +- VDUSE_INJECT_CONFIG_IRQ: inject a config interrupt + +Register VDUSE device on vDPA bus +--------------------------------- +In order to make the VDUSE device work, administrator needs to use the management +API (netlink) to register it on vDPA bus. Some sample codes are show below: + +.. code-block:: c + + static int netlink_add_vduse(const char *name, int device_id) + { + struct nl_sock *nlsock; + struct nl_msg *msg; + int famid; + + nlsock = nl_socket_alloc(); + if (!nlsock) + return -ENOMEM; + + if (genl_connect(nlsock)) + goto free_sock; + + famid = genl_ctrl_resolve(nlsock, VDPA_GENL_NAME); + if (famid < 0) + goto close_sock; + + msg = nlmsg_alloc(); + if (!msg) + goto close_sock; + + if (!genlmsg_put(msg, NL_AUTO_PORT, NL_AUTO_SEQ, famid, 0, 0, + VDPA_CMD_DEV_NEW, 0)) + goto nla_put_failure; + + NLA_PUT_STRING(msg, VDPA_ATTR_DEV_NAME, name); + NLA_PUT_STRING(msg, VDPA_ATTR_MGMTDEV_DEV_NAME, "vduse"); + NLA_PUT_U32(msg, VDPA_ATTR_DEV_ID, device_id); + + if (nl_send_sync(nlsock, msg)) + goto close_sock; + + nl_close(nlsock); + nl_socket_free(nlsock); + + return 0; + nla_put_failure: + nlmsg_free(msg); + close_sock: + nl_close(nlsock); + free_sock: + nl_socket_free(nlsock); + return -1; + } + +MMU-based IOMMU Driver +---------------------- +VDUSE framework implements an MMU-based on-chip IOMMU driver to support +mapping the kernel DMA buffer into the userspace iova region dynamically. +This is mainly designed for virtio-vdpa case (kernel virtio drivers). + +The basic idea behind this driver is treating MMU (VA->PA) as IOMMU (IOVA->PA). +The driver will set up MMU mapping instead of IOMMU mapping for the DMA transfer +so that the userspace process is able to use its virtual address to access +the DMA buffer in kernel. + +And to avoid security issue, a bounce-buffering mechanism is introduced to +prevent userspace accessing the original buffer directly which may contain other +kernel data. During the mapping, unmapping, the driver will copy the data from +the original buffer to the bounce buffer and back, depending on the direction of +the transfer. And the bounce-buffer addresses will be mapped into the user address +space instead of the original one. -- 2.11.0