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From: Xie Yongji <xieyongji@bytedance.com>
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	[thread overview]
Message-ID: <20210331080519.172-11-xieyongji@bytedance.com> (raw)
In-Reply-To: <20210331080519.172-1-xieyongji@bytedance.com>

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 <xieyongji@bytedance.com>
---
 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


  parent reply	other threads:[~2021-03-31  8:07 UTC|newest]

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-31  8:05 [PATCH v6 00/10] Introduce VDUSE - vDPA Device in Userspace Xie Yongji
2021-03-31  8:05 ` [PATCH v6 01/10] file: Export receive_fd() to modules Xie Yongji
2021-03-31  9:15   ` Christian Brauner
2021-03-31  9:26     ` Dan Carpenter
2021-03-31  9:28       ` Christian Brauner
2021-03-31 11:32     ` Yongji Xie
2021-03-31 12:23       ` Christian Brauner
2021-03-31 13:59         ` Yongji Xie
2021-03-31 14:07           ` Christian Brauner
2021-03-31 14:37             ` Yongji Xie
2021-03-31  8:05 ` [PATCH v6 02/10] eventfd: Increase the recursion depth of eventfd_signal() Xie Yongji
2021-03-31  8:05 ` [PATCH v6 03/10] vhost-vdpa: protect concurrent access to vhost device iotlb Xie Yongji
2021-04-09 16:15   ` Michael S. Tsirkin
2021-04-11  5:36     ` Yongji Xie
2021-04-11 20:48       ` Michael S. Tsirkin
2021-04-12  2:29         ` Yongji Xie
2021-04-12  9:00           ` Michael S. Tsirkin
2021-03-31  8:05 ` [PATCH v6 04/10] vhost-iotlb: Add an opaque pointer for vhost IOTLB Xie Yongji
2021-03-31  8:05 ` [PATCH v6 05/10] vdpa: Add an opaque pointer for vdpa_config_ops.dma_map() Xie Yongji
2021-03-31  8:05 ` [PATCH v6 06/10] vdpa: factor out vhost_vdpa_pa_map() and vhost_vdpa_pa_unmap() Xie Yongji
2021-03-31  8:05 ` [PATCH v6 07/10] vdpa: Support transferring virtual addressing during DMA mapping Xie Yongji
2021-04-08  2:36   ` Jason Wang
2021-03-31  8:05 ` [PATCH v6 08/10] vduse: Implement an MMU-based IOMMU driver Xie Yongji
2021-04-08  3:25   ` Jason Wang
2021-04-08  5:27     ` Yongji Xie
2021-03-31  8:05 ` [PATCH v6 09/10] vduse: Introduce VDUSE - vDPA Device in Userspace Xie Yongji
2021-04-08  6:57   ` Jason Wang
2021-04-08  9:36     ` Yongji Xie
2021-04-09  5:36       ` Jason Wang
2021-04-09  8:02         ` Yongji Xie
2021-04-12  7:16           ` Jason Wang
2021-04-12  8:02             ` Yongji Xie
2021-04-12  9:37               ` Jason Wang
2021-04-12  9:59                 ` Yongji Xie
2021-04-13  3:35                   ` Jason Wang
2021-04-13  4:28                     ` Yongji Xie
2021-04-14  8:18                       ` Jason Wang
2021-04-16  3:24   ` Jason Wang
2021-04-16  8:43     ` Yongji Xie
2021-03-31  8:05 ` Xie Yongji [this message]
2021-04-08  7:18   ` [PATCH v6 10/10] Documentation: Add documentation for VDUSE Jason Wang
2021-04-08  8:09     ` Yongji Xie
2021-04-14 14:14   ` Stefan Hajnoczi
2021-04-15  5:38     ` Yongji Xie
2021-04-15  7:19       ` Stefan Hajnoczi
2021-04-15  8:33         ` Yongji Xie
2021-04-15 14:17           ` Stefan Hajnoczi
2021-04-15  8:36         ` Jason Wang
2021-04-15  9:04           ` Jason Wang
2021-04-15 11:17             ` Yongji Xie
2021-04-16  2:20               ` Jason Wang
2021-04-16  2:58                 ` Yongji Xie
2021-04-16  3:02                   ` Jason Wang
2021-04-16  3:18                     ` Yongji Xie
2021-04-15 14:38           ` Stefan Hajnoczi
2021-04-16  2:23             ` Jason Wang
2021-04-16  3:19               ` Yongji Xie
2021-04-16  5:39                 ` Jason Wang
2021-04-16  3:13             ` Yongji Xie
2021-04-14  7:34 ` [PATCH v6 00/10] Introduce VDUSE - vDPA Device in Userspace Michael S. Tsirkin
2021-04-14  7:49   ` Jason Wang
2021-04-14  7:54   ` Yongji Xie

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