A memory leak occurs in the Vmwp.exe and Vmms.exe processes on a Windows Server 2008-based computer that has the Hyper-V role enabled


After you enable the Hyper-V role on a Windows Server 2008-based computer, the memory usage of the following processes continues to increase:
  • The Virtual Machine Worker process (Vmwp.exe)
  • The Virtual Machine Management Service process (Vmms.exe)
This behavior eventually causes the host computer to crash.


This problem occurs because the Performance Counter version 2.0 APIs that the Vmwp.exe and Vmms.exe processes use do not effectively manage allocated heaps. Therefore, a memory leak occurs.


A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing the problem described in this article. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.

If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, contact Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site: Note The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.

Important Windows Vista and Windows Server 2008 hotfixes are included in the same packages. However, only one of these products may be listed on the “Hotfix Request” page. To request the hotfix package that applies to both Windows Vista and Windows Server 2008, just select the product that is listed on the page.


To apply this hotfix, you must be running a version of Windows Server 2008 that has the Hyper-V role installed.

Restart requirement

You must restart the computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace any other hotfixes.

File information

The English version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time item in Control Panel.

Windows Server 2008 notes

The .manifest files and the .mum files that are installed in each environment are
listed separately
in the "Additional file information for Windows Server 2008" section. These files and their associated .cat (security catalog) files are critical to maintaining the state of the updated component. The .cat files are signed with a Microsoft digital signature. The attributes of these security files are not listed.
For all supported x64-based versions of Windows Server 2008
File nameFile versionFile sizeDateTimePlatformService branch
Advapi32.dll6.0.6001.223561,064,44817-Jan-200906:20x64Not applicable
Pdh.dll6.0.6001.22356307,71217-Jan-200906:28x64Not applicable
Pla.dll6.0.6001.223561,373,18417-Jan-200906:28x64Not applicable
Plamig.dll6.0.6001.22356103,42417-Jan-200906:29x64Not applicable
Plasrv.exe6.0.6001.223568,70417-Jan-200906:18x64Not applicable
Report.system.common.xmlNot applicable1,92718-Dec-200721:14Not applicableNot applicable
Report.system.configuration.xmlNot applicable27,57018-Dec-200721:14Not applicableNot applicable
Report.system.cpu.xmlNot applicable4,43818-Dec-200721:14Not applicableNot applicable
Report.system.diagnostics.xmlNot applicable7,24218-Dec-200721:14Not applicableNot applicable
Report.system.disk.xmlNot applicable3,19818-Dec-200721:14Not applicableNot applicable
Report.system.memory.xmlNot applicable4,82218-Dec-200721:14Not applicableNot applicable
Report.system.network.xmlNot applicable5,08818-Dec-200721:14Not applicableNot applicable
Report.system.performance.xmlNot applicable47118-Dec-200721:14Not applicableNot applicable
Report.system.summary.xmlNot applicable73818-Dec-200721:14Not applicableNot applicable
Rules.system.common.xmlNot applicable3,05918-Dec-200721:14Not applicableNot applicable
Rules.system.configuration.xmlNot applicable288,26918-Dec-200721:14Not applicableNot applicable
Rules.system.cpu.xmlNot applicable9,06218-Dec-200721:14Not applicableNot applicable
Rules.system.diagnostics.xmlNot applicable177,15018-Dec-200721:14Not applicableNot applicable
Rules.system.disk.xmlNot applicable6,25118-Dec-200721:14Not applicableNot applicable
Rules.system.finale.xmlNot applicable7,03618-Dec-200721:14Not applicableNot applicable
Rules.system.memory.xmlNot applicable12,91518-Dec-200721:14Not applicableNot applicable
Rules.system.network.xmlNot applicable3,35718-Dec-200721:14Not applicableNot applicable
Rules.system.performance.xmlNot applicable3,43418-Dec-200721:14Not applicableNot applicable
Rules.system.summary.xmlNot applicable18,54918-Dec-200721:14Not applicableNot applicable
System diagnostics.xmlNot applicable13,53918-Dec-200721:14Not applicableNot applicable
System performance.xmlNot applicable4,83018-Dec-200721:14Not applicableNot applicable
Pdhui.dll6.0.6001.2235658,88017-Jan-200906:28x64Not applicable
Perfmon.exe6.0.6001.22356124,92817-Jan-200906:18x64Not applicable
Perfmon.mscNot applicable145,45518-Dec-200721:15Not applicableNot applicable
Sysmon.ocx6.0.6001.22356476,67217-Jan-200906:17x64Not applicable
Wdc.dll6.0.6001.223561,234,43217-Jan-200906:30x64Not applicable
Wvc.dll6.0.6001.22356614,40017-Jan-200906:31x64Not applicable
Regsvc.dll6.0.6001.22356206,84817-Jan-200906:29x64Not applicable


To work around the issue, restart the Vmwp.exe and Vmms.exe processes, or restart the computer.


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

More Information

For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base: -
Description of the standard terminology that is used to describe Microsoft software updates

Additional file information for Windows Server 2008

Additional files for all supported x64-based versions of Windows Server 2008
File nameFile versionFile sizeDateTimePlatform
Amd64_microsoft-windows-advapi32_31bf3856ad364e35_6.0.6001.22356_none_3fc07fe5581fe7bd.manifestNot applicable9,85117-Jan-200909:40Not applicable
Amd64_microsoft-windows-p..rastructureconsumer_31bf3856ad364e35_6.0.6001.22356_none_1054bcda02103bea.manifestNot applicable168,92917-Jan-200909:42Not applicable
Amd64_microsoft-windows-performancetoolsgui_31bf3856ad364e35_6.0.6001.22356_none_f881ec6672921f1d.manifestNot applicable43,64717-Jan-200909:44Not applicable
Amd64_microsoft-windows-remoteregistry-service_31bf3856ad364e35_6.0.6001.22356_none_e5de33f45515800e.manifestNot applicable11,46817-Jan-200909:44Not applicable
Package_for_kb961730_sc_0~31bf3856ad364e35~amd64~~ applicable1,43018-Jan-200901:05Not applicable
Package_for_kb961730_sc~31bf3856ad364e35~amd64~~ applicable1,43118-Jan-200901:05Not applicable
Package_for_kb961730_server_0~31bf3856ad364e35~amd64~~ applicable1,43418-Jan-200901:05Not applicable
Package_for_kb961730_server~31bf3856ad364e35~amd64~~ applicable1,43918-Jan-200901:05Not applicable
Package_for_kb961730_winpesrv_0~31bf3856ad364e35~amd64~~ applicable1,43018-Jan-200901:05Not applicable
Package_for_kb961730_winpesrv~31bf3856ad364e35~amd64~~ applicable1,43818-Jan-200901:05Not applicable
Package_for_kb961730_winpe_0~31bf3856ad364e35~amd64~~ applicable1,42818-Jan-200901:05Not applicable
Package_for_kb961730_winpe~31bf3856ad364e35~amd64~~ applicable1,43218-Jan-200901:05Not applicable
Wow64_microsoft-windows-p..rastructureconsumer_31bf3856ad364e35_6.0.6001.22356_none_1aa9672c3670fde5.manifestNot applicable152,55517-Jan-200907:00Not applicable


Performance Counter version 2.0 APIs provide a new architecture for collecting Performance Counter data in Windows Vista and in Windows Server 2008.

For more information about Performance Counter version 2.0 APIs, visit the following Microsoft Developer Network (MSDN) Web site: For more information about how an application can provide Performance Counter data by using the Performance Counter version 2.0 APIs, visit the following MSDN Web site:

Article ID: 961730 - Last Review: May 27, 2009 - Revision: 1