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.

Prerequisites

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

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.

For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base: -

Additional file information for Windows Server 2008

Additional files for all supported x64-based versions of Windows Server 2008

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: