From patchwork Mon Mar 15 05:37:21 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Yongji Xie X-Patchwork-Id: 12138329 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=ham 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 CA77AC43603 for ; Mon, 15 Mar 2021 05:39:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B7B5C64E37 for ; Mon, 15 Mar 2021 05:39:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230285AbhCOFiu (ORCPT ); Mon, 15 Mar 2021 01:38:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49600 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230187AbhCOFib (ORCPT ); Mon, 15 Mar 2021 01:38:31 -0400 Received: from mail-pj1-x102a.google.com (mail-pj1-x102a.google.com [IPv6:2607:f8b0:4864:20::102a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E878FC061762 for ; Sun, 14 Mar 2021 22:38:30 -0700 (PDT) Received: by mail-pj1-x102a.google.com with SMTP id gb6so8165797pjb.0 for ; Sun, 14 Mar 2021 22:38:30 -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=lVG7vtvMbRMpvTShU3eF9/pmfbsuVpTNULn/mM9+dMw=; b=X4Katv61hXzWe/h3bbDQWPAQO+MiETrtLH9iH2sLpZRpl7F2JHyimf/FUJ29UjQADI /LZaO1zGI/9WVRVY+cmFhFmjEnvs2n8N+kRGoWjxIKubAFLqDfndDyq0otr0/G6wkgqO MUEqC3mUUFl1/WGlZfZZjPcsYBQWaGRaKdrB9GtVT6JwDT/7dvtAdM80/OnJza+1X3R+ a5KWUW95sUdB0zU9dOEwluTrVZeA+j13WV62gcbi7yM/Jf5+nma5ZcpAyc/Ig9G8FCwP dIfE/ozUv8SlBm35FchW29E/rQbzfLZPqejj8CooWPgaMzNe4h2es5r4z1Yx+O/nFhXq J9nQ== 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=lVG7vtvMbRMpvTShU3eF9/pmfbsuVpTNULn/mM9+dMw=; b=mJ/lAAW88sQsI+cDBng+2Bu+MNLYktKqVmGbgtMAn0ngKsOCkCIa9QYW2TuCrw8+d9 mlFod+e7/du6Zz3ftOXkXxjo+QDFpPqrk+w59xH1doGPVlFu/TBleU6yaD7IuVA0A+S8 XC1sFkd/I9PPBzO6E4Qugil60NncU3SVP9UBbh4CJYEA/GmaXCCWHPMYdAjYGlAgFBPX KVgGhDIHyOTKFYzCJ5Ob3Y8DiSqulTulDBDxHrifJoRSGWM/RxcU1BBlABHZxgPWDpMx /0Zim/5N+iO6nu+hXQD8xG/El9Rm4DSEQPM/rT/FPgIBBujXTyUAo814arDY6pSMmmgj LWTQ== X-Gm-Message-State: AOAM532LxYN6LDTM4l8dxRECk57EDmwsLDtd2xRizgu1xp3H5kWp9v2G 1C25GR0NiHwGZqIB63Eb0ufl X-Google-Smtp-Source: ABdhPJy0ZNV143F4ylJty11vzLVRq3Al/lgreCs5sIT9ATazkmI77l1xyiIl9kk/TpuIoUh/8F9Sjg== X-Received: by 2002:a17:902:6bca:b029:e2:c5d6:973e with SMTP id m10-20020a1709026bcab02900e2c5d6973emr9918682plt.40.1615786710484; Sun, 14 Mar 2021 22:38:30 -0700 (PDT) Received: from localhost ([139.177.225.227]) by smtp.gmail.com with ESMTPSA id o18sm8538438pji.10.2021.03.14.22.38.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 14 Mar 2021 22:38:30 -0700 (PDT) From: Xie Yongji To: mst@redhat.com, jasowang@redhat.com, stefanha@redhat.com, sgarzare@redhat.com, parav@nvidia.com, bob.liu@oracle.com, hch@infradead.org, 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 v5 11/11] Documentation: Add documentation for VDUSE Date: Mon, 15 Mar 2021 13:37:21 +0800 Message-Id: <20210315053721.189-12-xieyongji@bytedance.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210315053721.189-1-xieyongji@bytedance.com> References: <20210315053721.189-1-xieyongji@bytedance.com> MIME-Version: 1.0 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 | 209 ++++++++++++++++++++++++++++++++++ 2 files changed, 210 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..744a9d3452c1 --- /dev/null +++ b/Documentation/userspace-api/vduse.rst @@ -0,0 +1,209 @@ +================================== +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_ENTRY ioctl on the VDUSE device file: + +- VDUSE_IOTLB_GET_ENTRY: get a mmap'able iova region containing the specified iova. + Userspace can access this iova region by passing corresponding size, offset, perm + and fd 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) + { + void *addr; + size_t size; + struct vduse_iotlb_entry entry; + + entry.start = iova; + if (ioctl(dev_fd, VDUSE_IOTLB_GET_ENTRY, &entry)) + return NULL; + + size = entry.last - entry.start + 1; + *len = entry.last - iova + 1; + addr = mmap(0, size, perm_to_prot(entry.perm), MAP_SHARED, + entry.fd, entry.offset); + + 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.