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SMP virtual machines running Linux using the TSC clocksource stop responding or stall (1007020)


  • Guest operating system stops responding
  • Cannot perform actions on the guest operating system


Clocksource is the name of the new timekeeping subsystem introduced in the Linux 2.6.18 kernel. In this subsystem there are several clocksources that can be used to read the time. One of them is the tsc clocksource which uses the Time Stamp Counter that is present on each processor and can be used to track how much time has elapsed. The TSCs on the different processors are not necessarily perfectly in sync with each other, so time can appear to go backward if the TSC is read on one processor and then another processor. Early versions of the tsc clocksource did not handle this case, which can lead to the guest operating system not responding. Due to the different timing behavior of running in a virtual machine, this can be observed more frequently in a virtual machine.


Affected Kernels

Clocksource was introduced in 2.6.18 for 32 bit kernels and in 2.6.21 for 64 bit kernels. This issue is fixed in 2.6.26 for both 32 and 64 bit kernels. This is only an issue when using a virtual machine with more than one virtual CPU.

Affected Flavors and Versions

The following flavors/versions are affected:
  • Asianux 3 32 bit
  • CentOS 5.2 32 bit
  • CentOS 5.1 32 bit
  • CentOS 5.0 32 bit
  • Mandriva  Linux 2008 32 bit and 64 bit
  • Oracle Enterprise Linux 5 32 bit
  • RHEL 5.7
  • RHEL 5.6
  • RHEL 5.2 32 bit
  • RHEL 5.1 32 bit
  • RHEL 5.0 32 bit
  • SUSE Linux 10.3 32 bit and 64 bit
  • SUSE Linux 10.2 32 bit
  • Ubuntu 8.04 32 bit and 64 bit
  • Ubuntu 7.10 32 bit and 64 bit
  • Ubuntu 7.04 32 bit

The issue is fixed in a patch update for RHEL 5.2. For more information, see RHSA-2008:0519 - Security Advisory at

This issue is fixed in a patch update for Centos 5.2. For more information, see CentOS Errata and Security Advisory 2008:0519 at

Note: The preceding links were correct as of December 11, 2014. If you find the links are broken, please provide feedback and a VMware employee will update the link.  

This issue is fixed in Ubuntu 8.04.2.
This issue is fixed in Asianux 3 SP1 32bit.


The workaround for kernels with this issue is to use the acpi_pm clocksource. This can be done by putting clocksource=acpi_pm on the kernel command line.

See Also

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