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[Bug 1549494] Re: arm64: guest hangs when ntpd is running


This bug was fixed in the package linux - 4.4.0-21.37

linux (4.4.0-21.37) xenial; urgency=low

  [ Tim Gardner ]

  * Release Tracking Bug
    - LP: #1571791

  * linux: MokSBState is ignored (LP: #1571691)
    - SAUCE: (noup) MODSIGN: Import certificates from UEFI Secure Boot
    - SAUCE: (noup) efi: Disable secure boot if shim is in insecure mode
    - SAUCE: (noup) Display MOKSBState when disabled

linux (4.4.0-20.36) xenial; urgency=low

  [ Tim Gardner ]

  * Release Tracking Bug
    - LP: #1571069

  * sysfs mount failure during stateful lxd snapshots (LP: #1570906)
    - SAUCE: kernfs: Do not match superblock in another user namespace when

  * Kernel Panic in Ubuntu 16.04 netboot installer (LP: #1570441)
    - x86/topology: Fix logical package mapping
    - x86/topology: Fix Intel HT disable
    - x86/topology: Use total_cpus not nr_cpu_ids for logical packages
    - xen/apic: Provide Xen-specific version of cpu_present_to_apicid APIC op
    - x86/topology: Fix AMD core count

  * [regression]: Failed to call clock_adjtime(): Invalid argument
    (LP: #1566465)
    - ntp: Fix ADJ_SETOFFSET being used w/ ADJ_NANO

linux (4.4.0-19.35) xenial; urgency=low

  [ Tim Gardner ]

  * Release Tracking Bug
    - LP: #1570348

  * CVE-2016-2847 (LP: #1554260)
    - pipe: limit the per-user amount of pages allocated in pipes

  * xenial kernel crash on HP BL460c G7 (qla24xx problem?) (LP: #1554003)
    - SAUCE: (noup) qla2xxx: Add irq affinity notification V2

  * arm64: guest hangs when ntpd is running (LP: #1549494)
    - SAUCE: (noup) KVM: arm/arm64: Handle forward time correction gracefully

  * linux: Enforce signed module loading when UEFI secure boot (LP: #1566221)

  * s390/cpumf: Fix lpp detection (LP: #1555344)
    - s390/facilities: use stfl mnemonic instead of insn magic
    - s390/facilities: always use lowcore's stfle field for storing facility bits
    - s390/cpumf: Fix lpp detection

  * s390x kernel image needs weightwatchers (LP: #1536245)
    - [Config] s390x: Use compressed kernel bzImage

  * Surelock GA2 SP1: surelock02p05: Not seeing sgX devices for LUNs after
    upgrading to Ubuntu 16.04 (LP: #1567581)
    - Revert "UBUNTU: SAUCE: (noup) powerpc/pci: Assign fixed PHB number based on
      device-tree properties"

  * Backport upstream bugfixes to ubuntu-16.04 (LP: #1555765)
    - cpufreq: powernv: Define per_cpu chip pointer to optimize hot-path
    - Revert "cpufreq: postfix policy directory with the first CPU in related_cpus"
    - cpufreq: powernv: Add sysfs attributes to show throttle stats

  * systemd-modules-load.service: Failing due to missing module 'ib_iser' (LP: #1566468)
    - [Config] Add ib_iser to generic inclusion list

  * thunderx nic performance improvements (LP: #1567093)
    - net: thunderx: Set recevie buffer page usage count in bulk
    - net: thunderx: Adjust nicvf structure to reduce cache misses

  * fixes for thunderx nic in multiqueue mode (LP: #1567091)
    - net: thunderx: Fix for multiqset not configured upon interface toggle
    - net: thunderx: Fix for HW TSO not enabled for secondary qsets
    - net: thunderx: Fix receive packet stats

  * Miscellaneous Ubuntu changes
    - [Config] updateconfigs after CONFIG_DRM_I915_BPO_PRELIMINARY_HW_SUPPORT=n

  * Miscellaneous upstream changes (LP: #1564901)
    - Input: xpad - correctly handle concurrent LED and FF requests

 -- Tim Gardner <tim.gardner@xxxxxxxxxxxxx>  Mon, 18 Apr 2016 07:00:22

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

** CVE added: http://www.cve.mitre.org/cgi-

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  arm64: guest hangs when ntpd is running

Status in linux package in Ubuntu:
  Fix Released
Status in linux source package in Xenial:
  Fix Released

Bug description:
  SRU Justification:

  Impact: KVM guests hang on arm64 host running ntpd

  Fix: From linux-next:
  commit 1c5631c73fc2261a5df64a72c155cb53dcdc0c45
  Author: Marc Zyngier <marc.zyngier@xxxxxxx>
  Date:   Wed Apr 6 09:37:22 2016 +0100

      KVM: arm/arm64: Handle forward time correction gracefully
      BugLink: http://bugs.launchpad.net/bugs/1549494
      On a host that runs NTP, corrections can have a direct impact on
      the background timer that we program on the behalf of a vcpu.
      In particular, NTP performing a forward correction will result in
      a timer expiring sooner than expected from a guest point of view.
      Not a big deal, we kick the vcpu anyway.
      But on wake-up, the vcpu thread is going to perform a check to
      find out whether or not it should block. And at that point, the
      timer check is going to say "timer has not expired yet, go back
      to sleep". This results in the timer event being lost forever.
      There are multiple ways to handle this. One would be record that
      the timer has expired and let kvm_cpu_has_pending_timer return
      true in that case, but that would be fairly invasive. Another is
      to check for the "short sleep" condition in the hrtimer callback,
      and restart the timer for the remaining time when the condition
      is detected.
      This patch implements the latter, with a bit of refactoring in
      order to avoid too much code duplication.

  A) Install ntp on the host (I'm using a 2 socket ThunderX)
  B) Boot up a large VM (95 CPUs/4G memory)
  C) Within the VM, rebuild the Ubuntu kernel package
  If it doesn't hang - bug is gone.

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