From patchwork Tue Feb 23 11:50:46 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Yongji Xie X-Patchwork-Id: 12100267 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=-16.7 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 CC218C433DB for ; Tue, 23 Feb 2021 12:01:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8D34364E60 for ; Tue, 23 Feb 2021 12:01:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232614AbhBWMBt (ORCPT ); Tue, 23 Feb 2021 07:01:49 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52566 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232645AbhBWL4R (ORCPT ); Tue, 23 Feb 2021 06:56:17 -0500 Received: from mail-pl1-x636.google.com (mail-pl1-x636.google.com [IPv6:2607:f8b0:4864:20::636]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A79B2C0611BC for ; Tue, 23 Feb 2021 03:52:17 -0800 (PST) Received: by mail-pl1-x636.google.com with SMTP id g20so9686187plo.2 for ; Tue, 23 Feb 2021 03:52:17 -0800 (PST) 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=PDXwmR+zfUMQh4kl0+Ce33TRDCzTaQ5t8N+mpmSoLXc=; b=u5G5XB5qyZqOH8Mzw4gfHFjQYjH9mJkUDu4I4y9AOrknRK3kFJmO/o0JI4Y6ytVWoW Df4kZVvcduzlElzZMcpgRtMQqafV10iEnzwbvDTnSTeZ+1gmZp/9t5Hpvwngh/PJ6Ni2 N4njZBE3FbWpgtUAgtS5wS7gQ+0r9W5DFf7FgZCInETqlvvmas7mqGCKDwkf4WpZPH2h Ncl9Hga+Yoxu3QHJUGTNhXaVPI2rhngjoyZTOwwCc8XOy9KnZKfhASo83Z088wUnU5GR dzH2+aUF/2ALnw7qB/X8de87yvQOeBXOJK0NpvSynfYdfP6rsYr+2QkF0UU8DO39PGQs 70Ng== 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=PDXwmR+zfUMQh4kl0+Ce33TRDCzTaQ5t8N+mpmSoLXc=; b=YFy6XhsHHaKYbXo5HhbbuSGfxLP5bd99IUMJCGb1hgYUziOaePL3XOCoAicNFfE9mI 9vEAbAuNxBsJv/c1KOGRm7jCwjUXb/cAkx2UomwaMjFdnSD9GIpH7AGbG5Ta2f/UvPzq zLZIy0wpwhVUI+/AUJAEp5RYR31g0k5W8FekqJtypUDaaOZrdnGG3SqMFD6c2XjCHpFw xVdjRtwG0YV5obcZU3qETw7vsV1acmxbVpGhud7SVZCqCmptyHMQ/CRu1PnFHr6fuRXR KPZHQKQfhGYvRe/p5RHFSb4wTs3FKPrFkcjMjYAT+TDaxlu4VOidnwR/nK8cRzRS1OAD tIYQ== X-Gm-Message-State: AOAM531SutDUXtnDnQYGxbabobB52KwC3UgUDJMIjwYX1MtFXygkG3v/ UObWG4nQpADPKXwkb0ZB2IZa X-Google-Smtp-Source: ABdhPJwHrJOBCxe8WN55gZjE0Jk6w3901Z9CfOeQMD/HUMU3u/qMpB+2Q3e2U10DszPc7cAhQwwQBA== X-Received: by 2002:a17:90b:390b:: with SMTP id ob11mr29022804pjb.50.1614081137268; Tue, 23 Feb 2021 03:52:17 -0800 (PST) Received: from localhost ([139.177.225.253]) by smtp.gmail.com with ESMTPSA id mp17sm3098678pjb.48.2021.02.23.03.52.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 23 Feb 2021 03:52:16 -0800 (PST) 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 Cc: virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, kvm@vger.kernel.org, linux-aio@kvack.org, linux-fsdevel@vger.kernel.org Subject: [RFC v4 09/11] Documentation: Add documentation for VDUSE Date: Tue, 23 Feb 2021 19:50:46 +0800 Message-Id: <20210223115048.435-10-xieyongji@bytedance.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210223115048.435-1-xieyongji@bytedance.com> References: <20210223115048.435-1-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 | 112 ++++++++++++++++++++++++++++++++++ 2 files changed, 113 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..2a20e686bb59 --- /dev/null +++ b/Documentation/userspace-api/vduse.rst @@ -0,0 +1,112 @@ +================================== +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.unique; + + 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 deta 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 iova region. Userspace can + access this iova region by passing the fd to mmap(). + +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 + +MMU-based IOMMU Driver +---------------------- +In virtio-vdpa case, VDUSE framework implements an MMU-based on-chip IOMMU +driver to support mapping the kernel DMA buffer into the userspace iova +region dynamically. + +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.