On Tue, Aug 3, 2021 at 3:35 PM Jason Wang <jasowang@xxxxxxxxxx> wrote:
>
>
> 在 2021/7/29 下午3:35, Xie Yongji 写道:
> > 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@xxxxxxxxxxxxx>
> > ---
> > Documentation/userspace-api/index.rst | 1 +
> > Documentation/userspace-api/vduse.rst | 232 ++++++++++++++++++++++++++++++++++
> > 2 files changed, 233 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..30c9d1482126
> > --- /dev/null
> > +++ b/Documentation/userspace-api/vduse.rst
> > @@ -0,0 +1,232 @@
> > +==================================
> > +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.
> > +
> > +Create/Destroy VDUSE devices
> > +------------------------
> > +
> > +VDUSE devices are created 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 destroyed 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/$NAME.
> > +
> > +3. Destroy the VDUSE instance with ioctl(VDUSE_DESTROY_DEV) on
> > + /dev/vduse/control.
> > +
> > +The netlink messages can be sent via vdpa tool in iproute2 or use the
> > +below sample codes:
> > +
> > +.. code-block:: c
> > +
> > + static int netlink_add_vduse(const char *name, enum vdpa_command cmd)
> > + {
> > + struct nl_sock *nlsock;
> > + struct nl_msg *msg;
> > + int famid;
> > +
> > + nlsock = nl_socket_alloc();
> > + if (!nlsock)
> > + return -ENOMEM;
> > +
> > + if (genl_connect(nlsock))
> > + goto free_sock;
> > +
> > + famid = genl_ctrl_resolve(nlsock, VDPA_GENL_NAME);
> > + if (famid < 0)
> > + goto close_sock;
> > +
> > + msg = nlmsg_alloc();
> > + if (!msg)
> > + goto close_sock;
> > +
> > + if (!genlmsg_put(msg, NL_AUTO_PORT, NL_AUTO_SEQ, famid, 0, 0, cmd, 0))
> > + goto nla_put_failure;
> > +
> > + NLA_PUT_STRING(msg, VDPA_ATTR_DEV_NAME, name);
> > + if (cmd == VDPA_CMD_DEV_NEW)
> > + NLA_PUT_STRING(msg, VDPA_ATTR_MGMTDEV_DEV_NAME, "vduse");
> > +
> > + if (nl_send_sync(nlsock, msg))
> > + goto close_sock;
> > +
> > + nl_close(nlsock);
> > + nl_socket_free(nlsock);
> > +
> > + return 0;
> > + nla_put_failure:
> > + nlmsg_free(msg);
> > + close_sock:
> > + nl_close(nlsock);
> > + free_sock:
> > + nl_socket_free(nlsock);
> > + return -1;
> > + }
> > +
> > +How VDUSE works
> > +---------------
> > +
> > +As mentioned above, a VDUSE device is created by ioctl(VDUSE_CREATE_DEV) on
> > +/dev/vduse/control. With this ioctl, userspace can specify some basic configuration
> > +such as device name (uniquely identify a VDUSE device), virtio features, virtio
> > +configuration space, the number of virtqueues and so on for this emulated device.
> > +Then a char device interface (/dev/vduse/$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 messages */
> > +
> > + }
> > +
> > + 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_DEV_GET_FEATURES ioctl.
>
>
> I wonder if it's better to add a section about the future work?
>
> E.g the support for the userspace device to modify status (like
> NEEDS_RESET).
>
I prefer to document it after we add this new feature.
>
> > +
> > +- 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 as follows:
> > +
> > +1. Get the specified virtqueue's information with the VDUSE_VQ_GET_INFO ioctl,
> > + including the size, the IOVAs of descriptor table, available ring and used ring,
> > + the state and the ready status.
> > +
> > +2. Pass the above IOVAs to the VDUSE_IOTLB_GET_FD ioctl so that those IOVA regions
> > + can be mapped into userspace. Some sample codes is shown below:
> > +
> > +.. 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;
> > +
> > + /*
> > + * Find the first IOVA region that overlaps with the specified
> > + * range [start, last] and return the corresponding file descriptor.
> > + */
> > + 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;
> > + }
> > +
> > +3. Setup the kick eventfd for the specified virtqueues with the VDUSE_VQ_SETUP_KICKFD
> > + ioctl. The kick eventfd is used by VDUSE kernel module to notify userspace to
> > + consume the available ring.
> > +
> > +4. Listen to the kick eventfd and consume the available ring. The buffer described
> > + by the descriptors in the descriptor table should be also mapped into userspace
> > + via the VDUSE_IOTLB_GET_FD ioctl before accessing.
>
>
> (Or userspace may poll the indices instead, the kick eventfd is not a must).
>
OK, will add it.
Thanks,
Yongji
