[Bug 1888601] Re: QEMU v5.1.0-rc0/rc1 hang with nested virtualization

[Dr. David Alan Gilbert]

Seems an odd one to be the culprit? Still lets ask Jason.
Can you just clarify; is this qemu 5.1.0-rc on both the host and the kata, or 
are you just changing to using qemu 5.1 as the host, and you're sticking with 
the existing kata qemu?

Which host CPU have you got?

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Title:
  QEMU v5.1.0-rc0/rc1 hang with nested virtualization

Status in QEMU:
  New

Bug description:
  We're running Kata Containers using QEMU and with v5.1.0rc0 and rc1
  have noticed a problem at startup where QEMu appears to hang. We are
  not seeing this problem on our bare metal nodes and only on a VSI that
  supports nested virtualization.

  We unfortunately see nothing at all in the QEMU logs to help
  understand the problem and a hung process is just a guess at this
  point.

  Using git bisect we first see the problem with...

  ---

  f19bcdfedd53ee93412d535a842a89fa27cae7f2 is the first bad commit
  commit f19bcdfedd53ee93412d535a842a89fa27cae7f2
  Author: Jason Wang <jasowang@redhat.com>
  Date:   Wed Jul 1 22:55:28 2020 +0800

      virtio-pci: implement queue_enabled method

      With version 1, we can detect whether a queue is enabled via
      queue_enabled.

      Signed-off-by: Jason Wang <jasowang@redhat.com>
      Signed-off-by: Cindy Lu <lulu@redhat.com>
      Message-Id: <20200701145538.22333-5-lulu@redhat.com>
      Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
      Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
      Acked-by: Jason Wang <jasowang@redhat.com>

   hw/virtio/virtio-pci.c | 13 +++++++++++++
   1 file changed, 13 insertions(+)

  ---

  Reverting this commit (on top of 5.1.0-rc1) seems to work and prevent
  the hanging.

  ---

  Here's how kata ends up launching qemu in our environment --
  /opt/kata/bin/qemu-system-x86_64 -name 
sandbox-849df14c6065931adedb9d18bc9260a6d896f1814a8c5cfa239865772f1b7a5f -uuid 
6bec458e-1da7-4847-a5d7-5ab31d4d2465 -machine pc,accel=kvm,kernel_irqchip -cpu 
host,pmu=off -qmp 
unix:/run/vc/vm/849df14c6065931adedb9d18bc9260a6d896f1814a8c5cfa239865772f1b7a5f/qmp.sock,server,nowait
 -m 4096M,slots=10,maxmem=30978M -device 
pci-bridge,bus=pci.0,id=pci-bridge-0,chassis_nr=1,shpc=on,addr=2,romfile= 
-device virtio-serial-pci,disable-modern=true,id=serial0,romfile= -device 
virtconsole,chardev=charconsole0,id=console0 -chardev 
socket,id=charconsole0,path=/run/vc/vm/849df14c6065931adedb9d18bc9260a6d896f1814a8c5cfa239865772f1b7a5f/console.sock,server,nowait
 -device virtio-scsi-pci,id=scsi0,disable-modern=true,romfile= -object 
rng-random,id=rng0,filename=/dev/urandom -device 
virtio-rng-pci,rng=rng0,romfile= -device 
virtserialport,chardev=charch0,id=channel0,name=agent.channel.0 -chardev 
socket,id=charch0,path=/run/vc/vm/849df14c6065931adedb9d18bc9260a6d896f1814a8c5cfa239865772f1b7a5f/kata.sock,server,nowait
 -chardev 
socket,id=char-396c5c3e19e29353,path=/run/vc/vm/849df14c6065931adedb9d18bc9260a6d896f1814a8c5cfa239865772f1b7a5f/vhost-fs.sock
 -device 
vhost-user-fs-pci,chardev=char-396c5c3e19e29353,tag=kataShared,romfile= -netdev 
tap,id=network-0,vhost=on,vhostfds=3:4,fds=5:6 -device 
driver=virtio-net-pci,netdev=network-0,mac=52:ac:2d:02:1f:6f,disable-modern=true,mq=on,vectors=6,romfile=
 -global kvm-pit.lost_tick_policy=discard -vga none -no-user-config -nodefaults 
-nographic -daemonize -object 
memory-backend-file,id=dimm1,size=4096M,mem-path=/dev/shm,share=on -numa 
node,memdev=dimm1 -kernel /opt/kata/share/kata-containers/vmlinuz-5.7.9-74 
-initrd 
/opt/kata/share/kata-containers/kata-containers-initrd_alpine_1.11.2-6_agent.initrd
 -append tsc=reliable no_timer_check rcupdate.rcu_expedited=1 i8042.direct=1 
i8042.dumbkbd=1 i8042.nopnp=1 i8042.noaux=1 noreplace-smp reboot=k console=hvc0 
console=hvc1 iommu=off cryptomgr.notests net.ifnames=0 pci=lastbus=0 debug 
panic=1 nr_cpus=4 agent.use_vsock=false scsi_mod.scan=none 
init=/usr/bin/kata-agent -pidfile 
/run/vc/vm/849df14c6065931adedb9d18bc9260a6d896f1814a8c5cfa239865772f1b7a5f/pid 
-D 
/run/vc/vm/849df14c6065931adedb9d18bc9260a6d896f1814a8c5cfa239865772f1b7a5f/qemu.log
 -smp 2,cores=1,threads=1,sockets=4,maxcpus=4

  ---

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