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From: Yongji Xie <xieyongji@bytedance.com>
To: Jason Wang <jasowang@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
	"Stefan Hajnoczi" <stefanha@redhat.com>,
	"Stefano Garzarella" <sgarzare@redhat.com>,
	"Parav Pandit" <parav@nvidia.com>,
	"Christoph Hellwig" <hch@infradead.org>,
	"Christian Brauner" <christian.brauner@canonical.com>,
	"Randy Dunlap" <rdunlap@infradead.org>,
	"Matthew Wilcox" <willy@infradead.org>,
	"Al Viro" <viro@zeniv.linux.org.uk>,
	"Jens Axboe" <axboe@kernel.dk>,
	bcrl@kvack.org, "Jonathan Corbet" <corbet@lwn.net>,
	"Mika Penttilä" <mika.penttila@nextfour.com>,
	"Dan Carpenter" <dan.carpenter@oracle.com>,
	joro@8bytes.org, "Greg KH" <gregkh@linuxfoundation.org>,
	"He Zhe" <zhe.he@windriver.com>,
	"Liu Xiaodong" <xiaodong.liu@intel.com>,
	"Joe Perches" <joe@perches.com>,
	songmuchun@bytedance.com,
	virtualization <virtualization@lists.linux-foundation.org>,
	netdev@vger.kernel.org, kvm <kvm@vger.kernel.org>,
	linux-fsdevel@vger.kernel.org, iommu@lists.linux-foundation.org,
	linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v10 17/17] Documentation: Add documentation for VDUSE
Date: Tue, 3 Aug 2021 16:52:00 +0800	[thread overview]
Message-ID: <CACycT3uwBy3HY4at-d8Hg2v4ciSWLkhFU5Sk4AxzjbvNEY9mCg@mail.gmail.com> (raw)
In-Reply-To: <05365f36-bc3a-40f4-764d-37a7249b94b1@redhat.com>

On Tue, Aug 3, 2021 at 3:35 PM Jason Wang <jasowang@redhat.com> 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@bytedance.com>
> > ---
> >   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

      reply	other threads:[~2021-08-03  8:52 UTC|newest]

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-29  7:34 [PATCH v10 00/17] Introduce VDUSE - vDPA Device in Userspace Xie Yongji
2021-07-29  7:34 ` [PATCH v10 01/17] iova: Export alloc_iova_fast() and free_iova_fast() Xie Yongji
2021-08-03  7:41   ` Jason Wang
2021-08-03  7:41   ` Jason Wang
2021-08-03  8:54     ` Yongji Xie
2021-08-03 10:53       ` Robin Murphy
2021-08-04  5:02         ` Yongji Xie
2021-08-04 15:43           ` Robin Murphy
2021-08-05 12:34             ` Yongji Xie
2021-08-05 13:31               ` Jason Wang
2021-08-09  5:56                 ` Yongji Xie
2021-08-10  3:02                   ` Jason Wang
2021-08-10  7:43                     ` Yongji Xie
2021-07-29  7:34 ` [PATCH v10 02/17] file: Export receive_fd() to modules Xie Yongji
2021-08-03  7:45   ` Jason Wang
2021-08-03  9:01     ` Yongji Xie
2021-08-04  8:27       ` Jason Wang
2021-07-29  7:34 ` [PATCH v10 03/17] vdpa: Fix code indentation Xie Yongji
2021-08-03  7:50   ` Jason Wang
2021-08-03  9:13     ` Yongji Xie
2021-07-29  7:34 ` [PATCH v10 04/17] vdpa: Fail the vdpa_reset() if fail to set device status to zero Xie Yongji
2021-08-03  7:58   ` Jason Wang
2021-08-03  9:31     ` Yongji Xie
2021-08-04  8:30       ` Jason Wang
2021-07-29  7:34 ` [PATCH v10 05/17] vhost-vdpa: Fail the vhost_vdpa_set_status() on reset failure Xie Yongji
2021-08-03  8:10   ` Jason Wang
2021-08-03  9:50     ` Yongji Xie
2021-08-04  8:33       ` Jason Wang
2021-07-29  7:34 ` [PATCH v10 06/17] vhost-vdpa: Handle the failure of vdpa_reset() Xie Yongji
2021-07-29  7:34 ` [PATCH v10 07/17] virtio: Don't set FAILED status bit on device index allocation failure Xie Yongji
2021-08-03  8:02   ` Jason Wang
2021-08-03  9:17     ` Yongji Xie
2021-07-29  7:34 ` [PATCH v10 08/17] virtio_config: Add a return value to reset function Xie Yongji
2021-07-29  7:34 ` [PATCH v10 09/17] virtio-vdpa: Handle the failure of vdpa_reset() Xie Yongji
2021-07-29  7:34 ` [PATCH v10 10/17] virtio: Handle device reset failure in register_virtio_device() Xie Yongji
2021-08-03  8:09   ` Jason Wang
2021-08-03  9:38     ` Yongji Xie
2021-08-04  8:32       ` Jason Wang
2021-08-04  8:50         ` Yongji Xie
2021-08-04  8:54           ` Jason Wang
2021-08-04  9:07             ` Yongji Xie
2021-08-05  7:12               ` Jason Wang
2021-07-29  7:34 ` [PATCH v10 11/17] vhost-iotlb: Add an opaque pointer for vhost IOTLB Xie Yongji
2021-07-29  7:34 ` [PATCH v10 12/17] vdpa: Add an opaque pointer for vdpa_config_ops.dma_map() Xie Yongji
2021-07-29  7:34 ` [PATCH v10 13/17] vdpa: factor out vhost_vdpa_pa_map() and vhost_vdpa_pa_unmap() Xie Yongji
2021-07-29  7:35 ` [PATCH v10 14/17] vdpa: Support transferring virtual addressing during DMA mapping Xie Yongji
2021-07-29  7:35 ` [PATCH v10 15/17] vduse: Implement an MMU-based software IOTLB Xie Yongji
2021-07-29  7:35 ` [PATCH v10 16/17] vduse: Introduce VDUSE - vDPA Device in Userspace Xie Yongji
2021-07-29  9:00   ` Greg KH
2021-07-29  9:57     ` Yongji Xie
2021-08-03  7:30   ` Jason Wang
2021-08-03  8:39     ` Yongji Xie
2021-07-29  7:35 ` [PATCH v10 17/17] Documentation: Add documentation for VDUSE Xie Yongji
2021-08-03  7:35   ` Jason Wang
2021-08-03  8:52     ` Yongji Xie [this message]

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