From patchwork Mon May 17 09:55:13 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Yongji Xie X-Patchwork-Id: 12261417 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,URIBL_BLOCKED,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 8752DC433ED for ; Mon, 17 May 2021 09:58:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 56247610FC for ; Mon, 17 May 2021 09:58:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236495AbhEQJ7t (ORCPT ); Mon, 17 May 2021 05:59:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35262 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236461AbhEQJ7E (ORCPT ); Mon, 17 May 2021 05:59:04 -0400 Received: from mail-pg1-x530.google.com (mail-pg1-x530.google.com [IPv6:2607:f8b0:4864:20::530]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9D32BC0612ED for ; Mon, 17 May 2021 02:56:45 -0700 (PDT) Received: by mail-pg1-x530.google.com with SMTP id k15so4266954pgb.10 for ; Mon, 17 May 2021 02:56:45 -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=iU39BPoZqk2HqORX3UA9Ncb7R+Ai9Wci3A+87yTYnGc=; b=vJS0FLHo+jEjRSpl4KDvMAXIKV6coCiING2EQZA1u2Y7gKzBes8Am7G0tgOJgxQlrZ Bkdd4TMVPeYuCtXAnN7lHvgd+fGo5r7S18DNsqWRS/+zLqnQXdMn4+dWRtxgaHnmabi7 THQzQT3wQSsMuC7EE60tyCdc6m40mjKDwjpd/1WW7rO963r/zo6y3sBIX7e5E2Mp0D7e wV5rIuUrhiuPXFHAatRod8B2KEBFLN32CdPEoRTra2ZEhpJqs8EuDriMsfg43ibR1sFY E1p+zen4658VBftZ+03vFxrfs5JNVUwGNM8ZRnujdVaAFuKkf2tNZ8xNjzcx1TST/zJB o6mA== 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=iU39BPoZqk2HqORX3UA9Ncb7R+Ai9Wci3A+87yTYnGc=; b=RYN2K4gDm+x6gq43agR4h+Q0mi4NZEZiGVvy2AFx3Ji1aii421L8bUOVb0KANx/Jjy hPmdoEbi4hixKcm1wHzcGdiDf2jq95ymbIfuQ53n50Zm9l9OhPYovc9WhK3SPZ+G6zj7 wEoSRHkpxafGUJbTdkPO0FhtI1nYI5cV4NfNZwzHpTboGMe5EMpmQcCX/J77GDxvu8pS ingAz0d8YJV2PHnFK1fN3oyJIyYo8qvk0jyx9P2TbnvoFEGopqKC3Ly00q1Ri0PJmPrq L5wfj5godBr9pPv2eCJ0KTuL3iZX6CNWEkWmu/XT1sP8YWXw0ajXLv0onmhyOGBIYMjx pQBA== X-Gm-Message-State: AOAM531+KqDgXBY0PFzV2yIg0rLJn+jqPEBf/xhtA5b6KTmItE4R0n+d 9n5IFZB6HyGPxe/2E6m16Gvx X-Google-Smtp-Source: ABdhPJwaUmuqxTT6QOW1/dIV2zi3/klVmP6fV6W/ZGKjYhDf6qJpzO5wUPp9BNC/Sl2so2TDfCiGJg== X-Received: by 2002:a63:6f8e:: with SMTP id k136mr61696699pgc.326.1621245405101; Mon, 17 May 2021 02:56:45 -0700 (PDT) Received: from localhost ([139.177.225.253]) by smtp.gmail.com with ESMTPSA id v14sm10441643pgl.86.2021.05.17.02.56.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 May 2021 02:56:44 -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 Cc: 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 v7 12/12] Documentation: Add documentation for VDUSE Date: Mon, 17 May 2021 17:55:13 +0800 Message-Id: <20210517095513.850-13-xieyongji@bytedance.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210517095513.850-1-xieyongji@bytedance.com> References: <20210517095513.850-1-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 | 243 ++++++++++++++++++++++++++++++++++ 2 files changed, 244 insertions(+) create mode 100644 Documentation/userspace-api/vduse.rst diff --git a/Documentation/userspace-api/index.rst b/Documentation/userspace-api/index.rst index d29b020e5622..2dc25dd9f2aa 100644 --- a/Documentation/userspace-api/index.rst +++ b/Documentation/userspace-api/index.rst @@ -25,6 +25,7 @@ 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..a804be347545 --- /dev/null +++ b/Documentation/userspace-api/vduse.rst @@ -0,0 +1,243 @@ +================================== +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. + +In general, the userspace process that emulates the device is able to +run unprivileged. And to reduce security risks, we only support emulating +a few vDPA devices by default, including: virtio-net device, virtio-blk +device, virtio-scsi device and virtio-fs device. Only when a sysadmin trusts +the userspace process enough, it can relax the limitation with a +'allow_unsafe_device_emulation' module parameter. + +How VDUSE works +=============== + +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. Begin processing VDUSE messages from /dev/vduse/$NAME. The first + messages will arrive while attaching the VDUSE instance to vDPA. + +3. Send the VDPA_CMD_DEV_NEW netlink message to attach the VDUSE + instance to vDPA. + +VDUSE devices are stopped as follows: + +1. Send the VDPA_CMD_DEV_DEL netlink message to detach the VDUSE + instance to vDPA. + +2. Close the file descriptor referring to /dev/vduse/$NAME + +3. Destroy the VDUSE instance with ioctl(VDUSE_DESTROY_DEV) on + /dev/vduse/control + +The netlink messages metioned above 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; + } + +Emulate VDUSE devices +--------------------- + +To emulate a VDUSE device, we always need to implement both control path +and data path for it. + +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 /dev/vduse/$NAME to receive/reply those control messages +from/to VDUSE kernel module as follows: + +.. code-block:: c + + static int vduse_message_handler(int dev_fd) + { + int len; + struct vduse_dev_request req; + struct vduse_dev_response resp; + + len = read(dev_fd, &req, sizeof(req)); + if (len != sizeof(req)) + return -1; + + resp.request_id = req.request_id; + + switch (req.type) { + + /* handle different types of message */ + + } + + len = write(dev_fd, &resp, sizeof(resp)); + if (len != sizeof(resp)) + return -1; + + return 0; + } + +In the data path, vDPA device's iova regions will be mapped into userspace +with the help of VDUSE_IOTLB_GET_FD ioctl on /dev/vduse/$NAME: + +- 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 /dev/vduse/$NAME 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 + +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.