The latest cumulative update for Windows 10, which was released on March 1, appears to include one important change. Windows 10 KB4482887 (Build 17763.348) introduces “Retpoline” for Windows 10 version 1809 on certain devices and Microsoft plans to roll out the changes to more devices eventually.
Back in 2018, when Meltdown and Spectre vulnerabilities were discovered, Microsoft and other tech giants rolled out software updates to address the vulnerabilities. While the patch addressed the vulnerabilities, the reports revealed that mitigations could have an impact on performance, ranging between five and 30 percent.
To deal with the performance concerns, Google developed software-based mitigation called ‘Retpoline’ for Spectre Variant 2. The implementation of Retpoline is supposed to improve the performance of Spectre variant 2 mitigations in various platforms including Linux and Windows.
As Microsoft’s engineers also found this approach useful, the software maker began working on integrating Retpoline into the Windows last year.
Implementation of Retpoline is a big deal. The Retpoline and Microsoft’s own kernel modifications have reduced the performance impact to noise-level for most scenarios on Windows 10 devices.
Microsoft originally said that Retpoline will be integrated into Windows with the next version of the operating system, codenamed 19H1, which is due to come out in April 2019. But it appears that Microsoft also plans to ship changes to devices running the older version of Windows 10, starting with October 2018 Update.
Retpoline in Windows 10 October 2018 Update
In the changelog of KB4482887, Microsoft noted that it is the enabling of Retpoline “on certain devices” to improve the performance of Spectre variant 2 mitigations. However, the performance changes will be delivered to devices eventually as Microsoft is sticking to phased rollout approach.
With the latest cumulative update, Microsoft has backported the OS-level modifications needed to support Retpoline. In the next few months, Microsoft will begin enabling the feature via cloud configuration on more devices.
“Enables ‘Retpoline’ for Windows on certain devices, which may improve the performance of Spectre variant 2 mitigations (CVE-2017-5715),” the changelog reads.
“Today, we’re starting our phased roll out of Retpoline performance optimization for Spectre variant 2 mitigations to Windows 10 1809. As we’ve shared before, Windows 10 19H1 will ship with Retpoline enabled by default,” Microsoft’s Mehmet Iyigun explained.
In another blog post, Microsoft noted that Retpoline is currently disabled on production Windows 10 client devices. However, Microsoft says that it will begin pushing the changes to enable the feature over the coming months.
“While Retpoline is currently disabled by default on production Windows 10 client devices, we have backported the OS modifications needed to support Retpoline so that it can be used with Windows 10, version 1809 and have those modifications in the March 1, 2019 update,” Microsoft explains.
The performance impact of this change varies. For instance, it could speed up the Office app launch times by up to 25% on Broadwell CPUs.
As things aren’t that simple, Microsoft plans to enable Retpoline on more devices running Windows 10 October 2018 Update over the next few months. It’s worth noting that Retpoline will be also enabled by default in the next version of Windows 10, codenamed 19H1, which is due to come out in April 2019.