Ablu / xen-vhost-frontend

xen-vhost-frontend

Description

This program implements Xen specific vhost-user-frontend. This is PoC (proof-of-concept) implementation which lets us verify hypervisor-agnosticism of Rust based vhost-user backends.

This is only tested for AARCH64 until now.

Key components

• xen-vhost-frontend

  This is the Xen specific implementation of the vhost-user protocol, i.e. the current crate. This is designed based on the EPAM's virtio-disk implementation.

• Xen

  Enable following config options:

  diff --git a/xen/arch/arm/configs/arm64_defconfig b/xen/arch/arm/configs/arm64_defconfig
  index e69de29bb2d1..38ca05a8b416 100644
  --- a/xen/arch/arm/configs/arm64_defconfig
  +++ b/xen/arch/arm/configs/arm64_defconfig
  @@ -0,0 +1,3 @@
  +CONFIG_IOREQ_SERVER=y
  +CONFIG_EXPERT=y
  
  

  Latest tested HEAD:

  commit c8aaebccc8e8 ("tools/libxl: Fix virtio build error for 32-bit platforms")
  

• vhost-device

  These are Rust based vhost-user backends, maintained inside the rust-vmm project. These are not required to be modified based on hypervisor and are truly hypervisor-agnostic.

• Linux Kernel

  The current setup doesn't work with Vanilla kernel and needs some changes (hacks). This must be used for the Dom0 kernel. The same image can be used for guests too, but it is not mandatory.

Test Setup

The following steps lets one test I2C vhost-device on Xen.

• Build Xen for aarch64:

  $ ./configure --libdir=/usr/lib --build=x86_64-unknown-linux-gnu --host=aarch64-linux-gnu \
    --disable-docs --disable-golang --disable-ocamltools \
    --with-system-qemu=/root/qemu/build/i386-softmmu/qemu-system-i386
  
  $ make -j9 debball CROSS_COMPILE=aarch64-linux-gnu- XEN_TARGET_ARCH=arm64
  

• Run Xen via Qemu on X86 machine:

  $ qemu-system-aarch64 -machine virt,virtualization=on -cpu cortex-a57 -serial mon:stdio \
    -device virtio-net-pci,netdev=net0 -netdev user,id=net0,hostfwd=tcp::8022-:22 \
    -drive file=/home/debian-bullseye-arm64.qcow2,index=0,id=hd0,if=none,format=qcow2 \
    -device virtio-scsi-pci -device scsi-hd,drive=hd0 \
    -display none -m 8192 -smp 8 -kernel /home/xen/xen \
    -append "dom0_mem=5G,max:5G dom0_max_vcpus=7 loglvl=all guest_loglvl=all" \
    -device guest-loader,addr=0x46000000,kernel=/home/Image,bootargs="root=/dev/sda2 console=hvc0 earlyprintk=xen" \
    -device ds1338,address=0x20
  

  The ds1338 entry here is required to create a virtual I2C based RTC device on Dom0.

  This should get Dom0 up and running.

• Build xen-vhost-frontend crate:

  $ git clone https://github.com/vireshk/xen-vhost-frontend
  $ cd xen-vhost-frontend
  $ cargo build --release
  $ cd ../
  

• Build vhost-device crate:

  $ git clone https://github.com/rust-vmm/vhost-device
  $ cd vhost-device
  $ cargo build --release
  $ cd ../
  

• Setup I2C based RTC devices on Dom0

  This is required to control the device on Dom0 from the guest.

  $ echo ds1338 0x20 > /sys/bus/i2c/devices/i2c-0/new_device
  $ echo 0-0020 > /sys/bus/i2c/devices/0-0020/driver/unbind
  

• Lets run everything

  First start the I2C backend. This tells the I2C backend to hook up to /root/i2c.sock0 socket and wait for the master to start transacting. The I2C controller used here on Dom0 is named 90c0000.i2c (can be read from /sys/bus/i2c/devices/i2c-0/name) and 32 here matches the device on I2C bus set in the previous commands (0x20).

  $ /root/vhost-device/target/release/vhost-device-i2c -s /root/i2c.sock -c 1 -l 90c0000.i2c:32'
  

  Then start xen-vhost-frontend. This provides the path of the socket to the master side.

  $ /root/xen-vhost-frontend/target/release/xen-vhost-frontend --socket-path /root/'
  

  It supports I2C and GPIO for now. You can add support for more devices by adding a relevant entry in src/supported_devices.rs file.

  Now that all the preparations are done, lets start the guest. The guest kernel should have Virtio related config options enabled, along with i2c-virtio driver.

  $ xl create -c domu.conf
  

  The guest should boot now. Once the guest is up, you can create the I2C based RTC device and use it. Following will create /dev/rtc0 in the guest, which you can configure with the standard hwclock utility.

  $ echo ds1338 0x20 > /sys/bus/i2c/devices/i2c-0/new_device
  

Sample domu.conf

kernel="/root/Image"
memory=512
vcpus=3
command="console=hvc0 earlycon=xenboot"
name="domu"
virtio = [ "type=virtio,device22, transport=mmio" ]

The device type here defines the device to be emulated on the guest. The type value is set with the DT compatible string of the device. For example, it is virtio,device22 for I2C and virtio,device29 for GPIO.