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[Brad Figg <brad.figg@xxxxxxxxxxxxx>]

** Also affects: linux (Ubuntu Xenial)
   Importance: Undecided
       Status: New

** Changed in: linux (Ubuntu Xenial)
       Status: New => Fix Committed

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https://bugs.launchpad.net/bugs/1668594

Title:
  Recent KVM RTC cherry-picks break (some) Windows Live-Migrations

Status in linux package in Ubuntu:
  Triaged
Status in linux source package in Xenial:
  Fix Committed

Bug description:
  == SRU Justification ==

  Impact: Windows Live-Migration does not work reliably anymore with
  recent KVM RTC cherry-picks.

  Fix: Single follow-up upstream cherry pick which fixes the problem.

  Regression Potential: The patch has been upstream since 4.8, so it
  should be well-tested at this point. Thus regressions are unlikely.

  ---

  The fix for
  https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1649718 cherry-
  picked three commits from upstream 4.6 related to RTC interrupt
  handling. Unfortunately, the followup commit included in 4.8 was
  missed. As a result, Windwos Live-Migration in Qemu is broken on
  certain hardware.

  Test system's CPU:
   cat /proc/cpuinfo
  processor       : 0
  vendor_id       : GenuineIntel
  cpu family      : 6
  model           : 79
  model name      : Intel(R) Xeon(R) CPU E5-2620 v4 @ 2.10GHz
  stepping        : 1
  microcode       : 0xb00001b
  cpu MHz         : 1425.621
  cache size      : 20480 KB
  physical id     : 0
  siblings        : 16
  core id         : 0
  cpu cores       : 8
  apicid          : 0
  initial apicid  : 0
  fpu             : yes
  fpu_exception   : yes
  cpuid level     : 20
  wp              : yes
  flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch epb intel_pt tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 hle avx2 smep bmi2 erms invpcid rtm cqm rdseed adx smap xsaveopt cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local dtherm arat pln pts
  bugs            :
  bogomips        : 4199.88
  clflush size    : 64
  cache_alignment : 64
  address sizes   : 46 bits physical, 48 bits virtual
  power management:

  Live-Migrating a Windows Server 2016 VM (Qemu commandline below) hangs
  the VM in about 1/3 attempts. Interestingly, migrating the VM back to
  the original host allows the VM to run normally again (but subsequent
  migration attempts might hang it again as well).

  non-minimized qemu command line:
  /usr/bin/kvm -id 101 -chardev 'socket,id=qmp,path=/var/run/qemu-server/101.qmp,server,nowait' -mon 'chardev=qmp,mode=control' -pidfile /var/run/qemu-server/101.pid -daemonize -smbios 'type=1,uuid=a6e1bea5-09ab-4f8a-b1c2-3991725892f5' -drive 'if=pflash,unit=0,format=raw,readonly,file=/usr/share/kvm/OVMF_CODE-pure-efi.fd' -drive 'if=pflash,unit=1,format=raw,file=/tmp/101-ovmf.fd' -name Windows2016 -smp '2,sockets=1,cores=2,maxcpus=2' -nodefaults -boot 'menu=on,strict=on,reboot-timeout=1000,splash=/usr/share/qemu-server/bootsplash.jpg' -vga std -vnc unix:/var/run/qemu-server/101.vnc,x509,password -no-hpet -cpu 'host,+kvm_pv_unhalt,+kvm_pv_eoi,hv_spinlocks=0x1fff,hv_vapic,hv_time,hv_reset,hv_vpindex,hv_runtime,hv_relaxed' -m 2048 -k de -device 'pci-bridge,id=pci.1,chassis_nr=1,bus=pci.0,addr=0x1e' -device 'pci-bridge,id=pci.2,chassis_nr=2,bus=pci.0,addr=0x1f' -device 'piix3-usb-uhci,id=uhci,bus=pci.0,addr=0x1.0x2' -device 'usb-tablet,id=tablet,bus=uhci.0,port=1' -chardev 'socket,path=/var/run/qemu-server/101.qga,server,nowait,id=qga0' -device 'virtio-serial,id=qga0,bus=pci.0,addr=0x8' -device 'virtserialport,chardev=qga0,name=org.qemu.guest_agent.0' -device 'virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3' -iscsi 'initiator-name=iqn.1993-08.org.debian:01:98525b424092' -drive 'file=PATH,if=none,id=drive-ide2,media=cdrom,aio=threads' -device 'ide-cd,bus=ide.1,unit=0,drive=drive-ide2,id=ide2,bootindex=200' -device 'virtio-scsi-pci,id=scsihw0,bus=pci.0,addr=0x5' -drive 'file=PATH,if=none,id=drive-scsi0,cache=writeback,discard=on,format=raw,aio=threads,detect-zeroes=unmap' -device 'scsi-hd,bus=scsihw0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0,id=scsi0,bootindex=100' -netdev 'type=tap,id=net0,ifname=tap101i0,script=/var/lib/qemu-server/pve-bridge,downscript=/var/lib/qemu-server/pve-bridgedown,vhost=on' -device 'virtio-net-pci,mac=32:F5:16:78:A7:F0,netdev=net0,bus=pci.0,addr=0x12,id=net0,bootindex=300' -rtc 'driftfix=slew,base=localtime' -global 'kvm-pit.lost_tick_policy=discard'

  The causing commits were triaged via git bisect, applying the follow-
  up commit b0eaf4506f5f95d15d6731d72c0ddf4a2179eefa fixes the issue
  with no observable side-effects. Mainline 4.6 is also affected and
  triggers the bug just like Ubuntu kernels >= Ubuntu-4.4.0-63.84

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