CMPXCHG16B is not provided to Windows Server 2019 guests

[fth0]

The hack in ConsoleImpl2.cpp?rev=86506#L936 obviously cannot work for "Windows 2019 (64-bit)" as "Guest OS Version". The Windows Server 2019 installer runs up to an INT3, leading to a Guru Meditation (see forum topic ​VMs crash when VM OS Version set to Window 2019 for a VBox.log file if necessary).

[fth0]

In the case of the forum user, the host CPU is missing the Unrestricted Guest CPU feature. In consequence, VirtualBox doesn't provide the CX16 CPU feature to the guest OS. When the Guest OS Version is configured as "Windows 2016 (64-bit)", the CX16 CPU feature is provided to the guest OS because of the hack, and the crash doesn't happen.

Disclaimer: The term hack is copied from the VirtualBox source code referenced in the description. ;)

[Klaus Espenlaub]

Thanks for the reminder today... we clearly missed both the forum posts and this ticket.

In the latest 6.1 Testbuilds this should be fixed (for good, because the reasons why we had to handle it in a hacky way have been eliminated quite a while ago). The same builds also have a fix for the forgotten adaption of the Paravirt Provider default (HyperV) for Windows Server 2016 and 2019. Not quite as much "for good", but should still last a while.

Revision 145326 or later has the change.

[fth0]

I confirm that this issue is fixed with VirtualBox 6.1.23r145326: For a Windows Server 2019 guest, the effective paravirtualization provider is now "HyperV", CX16 (CMPXCHG16B) is provided to the guest, and the Windows Server 2019 installation ISO boots successfully up to the installer, instead of executing INT3 leading to the Guru Meditation.

FWIW, during my tests, I once encountered a BSOD in the Windows memory management, but it wasn't reproducible and the VM didn't crash.

Thanks a lot for addressing this issue, which was recurring regularly in the VirtualBox forums.

[fth0]

I confirm that this issue is fixed in VirtualBox 6.1.24.