[vbox-dev] VirtualBox on Win 10 with Hyper-V/CredentialsGuard enabled

Ramshankar ramshankar.venkataraman at oracle.com
Wed Mar 22 02:50:37 UTC 2017

If VirtualBox causes a BSOD regardless of whether VT-x has been grabbed 
by Hyper-V or any other program, it should be considered a bug.

If VirtualBox is merely refusing to start the VM in hardware virtualized 
mode, then that's normal and that's not something we can do anything 
about until Microsoft changes Hyper-V to relinquish VT-x when it's not 
being used (which I suspect isn't simple for them to do, as Hyper-V is 
probably a "type 1" and it can't do that without disabling Hyper-V 
altogether and doing a reboot of the system).

VirtualBox already plays nice on Windows by default[1], by only turning 
on VT-x when executing guest code and switching VT-x off when VirtualBox 
gets back to executing host-context code. This way when a VirtualBox 
virtual-CPU thread isn't executing guest code anyone is free to use VT-x.


As for running 32-bit VMs without VT-x that really should work. What 
error are you getting in this case? Could you attach the VBox.log for 
the VM in question?


[1] -- This can be seen by checking the output of VBoxManage list 
systemproperties and looking at "Exclusive HW virtualization" (it should 
be "on" on Windows hosts by default).

On 03/21/2017 03:47 PM, Mikhail Kovalev wrote:
> Hello,
> in the current state VirtualBox doesn't work on Win10 in case if 
> Hyper-V is enabled. I do understand that VT-x is not available for 
> VirtualBox in that case, but at least the 32-bit VMs could work 
> without VT-x.
> In the bug ticket #15780, Frank wrote
> "VirtualBox <https://www.virtualbox.org/wiki/VirtualBox>is trying to 
> change the CR4 value but the host crashes try to do so. The reason is 
> most likely that Hyper-V is active. Please try to disable Hyper-V".
> So this is a Hyper-V bug and nothing can be done on the VirtualBox 
> side to fix this? Or is there a chance that this problem will get 
> fixed in the upcoming releases of VirtualBox?
> If I additionally enable the CredentialsGuard with Virtualization 
> Based Protection for Code Integrity (without activating Code Integrity 
> Policies) on Win 10, then VirtualBox crashes even earlier with "Failed 
> to load VMMR0.r0". I guess this is a different issue and it's 
> unrelated to the BSOD. I would create a bug ticket for that, but it 
> probably doesn't make much sense currently because of the BSOD problem.
> Thnx & best regards,
> Mikhail
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> vbox-dev at virtualbox.org
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