[Bug 1888818] Re: Multi-queue vhost-user fails to reconnect with qemu version >=4.2

[Thomas Huth <1888818@bugs.launchpad.net>]

The QEMU project is currently moving its bug tracking to another system.
For this we need to know which bugs are still valid and which could be
closed already. Thus we are setting the bug state to "Incomplete" now.

If the bug has already been fixed in the latest upstream version of QEMU,
then please close this ticket as "Fix released".

If it is not fixed yet and you think that this bug report here is still
valid, then you have two options:

1) If you already have an account on gitlab.com, please open a new ticket
for this problem in our new tracker here:

    https://gitlab.com/qemu-project/qemu/-/issues

and then close this ticket here on Launchpad (or let it expire auto-
matically after 60 days). Please mention the URL of this bug ticket on
Launchpad in the new ticket on GitLab.

2) If you don't have an account on gitlab.com and don't intend to get
one, but still would like to keep this ticket opened, then please switch
the state back to "New" within the next 60 days (otherwise it will get
closed as "Expired"). We will then eventually migrate the ticket auto-
matically to the new system (but you won't be the reporter of the bug
in the new system and thus won't get notified on changes anymore).

Thank you and sorry for the inconvenience.


** Changed in: qemu
       Status: New => Incomplete

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https://bugs.launchpad.net/bugs/1888818

Title:
  Multi-queue vhost-user fails to reconnect with qemu version >=4.2

Status in QEMU:
  Incomplete

Bug description:
  Test Environment:
  DPDK version: DPDK v20.08
  Other software versions: qemu4.2.0, qemu5.0.0.
  OS: Linux 4.15.0-20-generic
  Compiler: gcc (Ubuntu 7.3.0-16ubuntu3) 8.4.0
  Hardware platform: Purley.
  Test Setup
  Steps to reproduce
  List the steps to reproduce the issue.

  Test flow
  =========
  1. Launch vhost-user testpmd as port0 with 2 queues:

  ./x86_64-native-linuxapp-gcc/app/testpmd -l 2-4 -n 4 \
      --file-prefix=vhost --vdev 'net_vhost0,iface=vhost-net,queues=2,client=1' -- -i --txd=1024 --rxd=1024 --txq=2 --rxq=2
  testpmd>start

  3. Launch qemu with virtio-net:

   taskset -c 13 \
      qemu-system-x86_64 -name us-vhost-vm1 \
         -cpu host -enable-kvm -m 2048 -object memory-backend-file,id=mem,size=2048M,mem-path=/mnt/huge,share=on \
         -numa node,memdev=mem \
         -mem-prealloc -monitor unix:/tmp/vm2_monitor.sock,server,nowait -netdev user,id=yinan,hostfwd=tcp:127.0.0.1:6005-:22 -device e1000,netdev=yinan \
         -smp cores=1,sockets=1 -drive file=/home/osimg/ubuntu16.img  \
         -chardev socket,id=char0,path=./vhost-net,server \
         -netdev type=vhost-user,id=mynet1,chardev=char0,vhostforce,queues=2 \
         -device virtio-net-pci,mac=52:54:00:00:00:01,netdev=mynet1,mrg_rxbuf=on,csum=on,gso=on,host_tso4=on,guest_tso4=on,mq=on,vectors=15 \
         -vnc :10 -daemonize

  6. Quit testpmd and restart vhost-user :

  testpmd>quit
  ./x86_64-native-linuxapp-gcc/app/testpmd -l 2-4 -n 4 \
      --file-prefix=vhost --vdev 'net_vhost0,iface=vhost-net,queues=2,client=1' -- -i --txd=1024 --rxd=1024 --txq=2 --rxq=2

  Expected Result:
  After the vhost-user is killed then re-launched, the virtio-net can connect back to vhost-user again.

  Actual Result:
  Vhost-user relaunch failed with continous log printed"VHOST_CONFIG: Processing VHOST_USER_SET_FEATURES failed.

  Analysis:
  This is a regression bug, bad commit: c6beefd674f
  When vhost-user quits, QEMU doesnot save acked features for each virtio-net after vhost-user quits. When vhost-user reconnects to QEMU, QEMU sends two different features(one is the true acked feature while the another is 0x40000000) to vhost-user successively which causing vhost-user exits abnormally.

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