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

[Simon Kaegi]

I believe the VSI itself is QEMU based but don't know the version or
details but suspect it's 4.1 based. We compile our own QEMU version for
use with Kata and that's where we're now using 5.1.0-rc1 with the above
commit reverted.

Host Kernel is ... 4.15.0-101-generic if that helps

re: cpu -- four of these...
```
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 6
model           : 61
model name      : Intel Core Processor (Broadwell, IBRS)
stepping        : 2
microcode       : 0x1
cpu MHz         : 2095.148
cache size      : 16384 KB
physical id     : 0
siblings        : 4
core id         : 0
cpu cores       : 2
apicid          : 0
initial apicid  : 0
fpu             : yes
fpu_exception   : yes
cpuid level     : 13
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov 
pat pse36 clflush mmx fxsr sse sse2 ss ht syscall nx pdpe1gb rdtscp lm 
constant_tsc rep_good nopl xtopology cpuid tsc_known_freq pni pclmulqdq vmx 
ssse3 fma cx16 pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes 
xsave avx f16c rdrand hypervisor lahf_lm abm 3dnowprefetch cpuid_fault 
invpcid_single pti ssbd ibrs ibpb tpr_shadow vnmi flexpriority ept vpid 
fsgsbase tsc_adjust bmi1 hle avx2 smep bmi2 erms invpcid rtm rdseed adx smap 
xsaveopt arat md_clear
bugs            : cpu_meltdown spectre_v1 spectre_v2 spec_store_bypass l1tf mds 
swapgs taa itlb_multihit
bogomips        : 4190.29
clflush size    : 64
cache_alignment : 64
address sizes   : 40 bits physical, 48 bits virtual
power management:
```

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https://bugs.launchpad.net/bugs/1888601

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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