From patchwork Tue Jul 13 08:46:56 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Yongji Xie X-Patchwork-Id: 12373237 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 9A62BC07E95 for ; Tue, 13 Jul 2021 08:49:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 84AC2613A9 for ; Tue, 13 Jul 2021 08:49:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235025AbhGMIwK (ORCPT ); Tue, 13 Jul 2021 04:52:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50266 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235260AbhGMIvo (ORCPT ); Tue, 13 Jul 2021 04:51:44 -0400 Received: from mail-pj1-x1034.google.com (mail-pj1-x1034.google.com [IPv6:2607:f8b0:4864:20::1034]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 650BCC06178A for ; Tue, 13 Jul 2021 01:48:27 -0700 (PDT) Received: by mail-pj1-x1034.google.com with SMTP id p4-20020a17090a9304b029016f3020d867so1655838pjo.3 for ; Tue, 13 Jul 2021 01:48:27 -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=uMm6a9p0EzX9DUYqGCBIk5+JBvK8mtKaW/5v/siepz8=; b=FwrQiD+0uRPLUN+6Ju88xP5C02Bvk9OqVShw9WcsJdiLxu+YCLfDld1XCGfjLU1nSl 918yKE4A5ColszxQDG/4pM1sXcDtN4ghfirvX+RsqtkNJyYamqqNi2VjbvDtJuJMdMEH DBnVAKFBCd1A3Mu8H5eyl/2LzIPpp/+RJW7nXs1sv+9wD9NX2G2ZW51nr6oAKS/uh/Re no24BT5m/sJN3evL+WSKCld+Bzy52NIw84s+0QKBgTE+n5jtfL7elaULaVgn89viBuwz oYoSGCLRyfky8JDQWJQ44g6XrECuYo7lecJLBNwO2UB7NYtQMZoIpWP32eSw3XP6Zz0y tt/w== 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=uMm6a9p0EzX9DUYqGCBIk5+JBvK8mtKaW/5v/siepz8=; b=aonyuO/MjhTsvmkPJmJ8nFBiXBG/vuCxVQrjRK1HH6ig/YJcswtY4LJFQgh9hG1JjB hq1sJ7dh2q1FyUzcNcAHXj3iNx29OHbsNIiLOiKyJOOyCv9NGixUbmd/Bnkvv871fHlb eZTJElr88A8Y//mLhQrkkJ27QtytYi8ddyvDu8lGlnpR0jLsrfPzWD4J+8PMBZaAp3y2 H4DZyHU28fPm6jJnbYw7k0MygdqYtv65g2gAqGj+SwFI/XtH9i6dsVVnKnANWXyMoljx V0UkVupMBraReQazZ/EMfdpAoXW5Nb6AVPHdHoW+uDoUb8gsJbozqPOF1kAjCspqDmcl sX5w== X-Gm-Message-State: AOAM5307uUToVezxZRXR3B1yCfQt+VFZF9wR25SSn089W2IYy8I/9XG9 d3Y4o37MgHMjVF++7bRa9AjP X-Google-Smtp-Source: ABdhPJy41kKAoDHW9SvVVXjbdWKoO4Hb5f5MeAoUzDaUJYwvEJY6gTCT1v+c76dyqcdtmYhkN5UdhA== X-Received: by 2002:a17:90a:8585:: with SMTP id m5mr3319949pjn.224.1626166106915; Tue, 13 Jul 2021 01:48:26 -0700 (PDT) Received: from localhost ([139.177.225.253]) by smtp.gmail.com with ESMTPSA id a23sm17961927pff.43.2021.07.13.01.48.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 13 Jul 2021 01:48:26 -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, joro@8bytes.org, gregkh@linuxfoundation.org, zhe.he@windriver.com, xiaodong.liu@intel.com Cc: songmuchun@bytedance.com, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, kvm@vger.kernel.org, linux-fsdevel@vger.kernel.org, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: [PATCH v9 17/17] Documentation: Add documentation for VDUSE Date: Tue, 13 Jul 2021 16:46:56 +0800 Message-Id: <20210713084656.232-18-xieyongji@bytedance.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210713084656.232-1-xieyongji@bytedance.com> References: <20210713084656.232-1-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 | 248 ++++++++++++++++++++++++++++++++++ 2 files changed, 249 insertions(+) create mode 100644 Documentation/userspace-api/vduse.rst diff --git a/Documentation/userspace-api/index.rst b/Documentation/userspace-api/index.rst index 0b5eefed027e..c432be070f67 100644 --- a/Documentation/userspace-api/index.rst +++ b/Documentation/userspace-api/index.rst @@ -27,6 +27,7 @@ place where this information is gathered. iommu media/index sysfs-platform_profile + 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..2c0d56d4b2da --- /dev/null +++ b/Documentation/userspace-api/vduse.rst @@ -0,0 +1,248 @@ +================================== +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. And +to make the device emulation more secure, the emulated vDPA device's +control path is handled in the kernel and only the data path is +implemented in the userspace. + +Note that only virtio block device is supported by VDUSE framework now, +which can reduce security risks when the userspace process that implements +the data path is run by an unprivileged user. The support for other device +types can be added after the security issue of corresponding device driver +is clarified or fixed in the future. + +Start/Stop VDUSE devices +------------------------ + +VDUSE devices are started as follows: + +1. Create a new VDUSE instance with ioctl(VDUSE_CREATE_DEV) on + /dev/vduse/control. + +2. Setup each virtqueue with ioctl(VDUSE_VQ_SETUP) on /dev/vduse/$NAME. + +3. Begin processing VDUSE messages from /dev/vduse/$NAME. The first + messages will arrive while attaching the VDUSE instance to vDPA bus. + +4. Send the VDPA_CMD_DEV_NEW netlink message to attach the VDUSE + instance to vDPA bus. + +VDUSE devices are stopped as follows: + +1. Send the VDPA_CMD_DEV_DEL netlink message to detach the VDUSE + instance from vDPA bus. + +2. Close the file descriptor referring to /dev/vduse/$NAME. + +3. Destroy the VDUSE instance with ioctl(VDUSE_DESTROY_DEV) on + /dev/vduse/control. + +The netlink messages can be sent via vdpa tool in iproute2 or use the +below sample codes: + +.. code-block:: c + + static int netlink_add_vduse(const char *name, enum vdpa_command cmd) + { + struct nl_sock *nlsock; + struct nl_msg *msg; + int famid; + + nlsock = nl_socket_alloc(); + if (!nlsock) + return -ENOMEM; + + if (genl_connect(nlsock)) + goto free_sock; + + famid = genl_ctrl_resolve(nlsock, VDPA_GENL_NAME); + if (famid < 0) + goto close_sock; + + msg = nlmsg_alloc(); + if (!msg) + goto close_sock; + + if (!genlmsg_put(msg, NL_AUTO_PORT, NL_AUTO_SEQ, famid, 0, 0, cmd, 0)) + goto nla_put_failure; + + NLA_PUT_STRING(msg, VDPA_ATTR_DEV_NAME, name); + if (cmd == VDPA_CMD_DEV_NEW) + NLA_PUT_STRING(msg, VDPA_ATTR_MGMTDEV_DEV_NAME, "vduse"); + + if (nl_send_sync(nlsock, msg)) + goto close_sock; + + nl_close(nlsock); + nl_socket_free(nlsock); + + return 0; + nla_put_failure: + nlmsg_free(msg); + close_sock: + nl_close(nlsock); + free_sock: + nl_socket_free(nlsock); + return -1; + } + +How VDUSE works +--------------- + +As mentioned above, a VDUSE device is created by ioctl(VDUSE_CREATE_DEV) on +/dev/vduse/control. With this ioctl, userspace can specify some basic configuration +such as device name (uniquely identify a VDUSE device), virtio features, virtio +configuration space, bounce buffer size and so on for this emulated device. Then +a char device interface (/dev/vduse/$NAME) is exported to userspace for device +emulation. Userspace can use the VDUSE_VQ_SETUP ioctl on /dev/vduse/$NAME to +add per-virtqueue configuration such as the max size of virtqueue to the device. + +After the initialization, the VDUSE device can be attached to vDPA bus via +the VDPA_CMD_DEV_NEW netlink message. Userspace needs to read()/write() on +/dev/vduse/$NAME to receive/reply some 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; + } + +There are now three types of messages introduced by VDUSE framework: + +- VDUSE_GET_VQ_STATE: Get the state for virtqueue, userspace should return + avail index for split virtqueue or the device/driver ring wrap counters and + the avail and used index for packed virtqueue. + +- VDUSE_SET_STATUS: Set the device status, userspace should follow + the virtio spec: https://docs.oasis-open.org/virtio/virtio/v1.1/virtio-v1.1.html + to process this message. For example, fail to set the FEATURES_OK device + status bit if the device can not accept the negotiated virtio features + get from the VDUSE_GET_FEATURES ioctl. + +- VDUSE_UPDATE_IOTLB: Notify userspace to update the memory mapping for specified + IOVA range, userspace should firstly remove the old mapping, then setup the new + mapping via the VDUSE_IOTLB_GET_FD ioctl. + +After DRIVER_OK status bit is set via the VDUSE_SET_STATUS message, userspace is +able to start the dataplane processing with the help of below ioctls: + +- VDUSE_IOTLB_GET_FD: Find the first IOVA region that overlaps with the specified + range [start, last] and return the corresponding file descriptor. In vhost-vdpa + cases, it might be a full chunk of guest RAM. And in virtio-vdpa cases, it should + be the whole bounce buffer or the memory region that stores one virtqueue's + metadata (descriptor table, available ring and used ring). 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; + 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; + + /* + * Using some data structures such as linked list to store + * the iotlb mapping. The munmap(2) should be called for the + * cached mapping when the corresponding VDUSE_UPDATE_IOTLB + * message is received or the device is reset. + */ + + return addr + iova - entry.start; + } + +- VDUSE_VQ_GET_INFO: Get the specified virtqueue's information including the size, + the IOVAs of descriptor table, available ring and used ring, the state + and the ready status. The IOVAs should be passed to the VDUSE_IOTLB_GET_FD ioctl + so that userspace can access the descriptor table, available ring and used ring. + +- VDUSE_VQ_SETUP_KICKFD: Setup the kick eventfd for the specified virtqueues. + The kick eventfd is used by VDUSE kernel module to notify userspace to consume + the available ring. + +- VDUSE_INJECT_VQ_IRQ: Inject an interrupt for specific virtqueue. It's used to + notify virtio driver to consume the used ring. + +More details on the uAPI can be found in include/uapi/linux/vduse.h. + +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.