INACCESSIBLE_BOOT_DEVICE after enabling Hyper-V in Windows 10 on Late-2015 27" 5k iMac

Although it seems like a long-shot, I guess I could try it. Need to buy myself one of those, though. I'll share the results when I've tried it!

Any update on this? Anyone figure out how to get this working? Or is Apple abandoning us?

BiggStuu wrote:

Any update on this? Anyone figure out how to get this working? Or is Apple abandoning us?

What is the year/model of your Mac? What is the version of Windows?

2K15 imac 5K, Win10 x64

The older Macs with CSM-BIOS will support, but the newer UEFI Macs do not support it. Please also see https://msdn.microsoft.com/virtualization/hyperv_on_windows/quick_start/walkthro ugh_compatibility

From the OP

Note: I also happen to have an older iMac running Windows 10 that runs fine with Hyper-V enabled. I really need Hyper-V support as I have to get those emulaters running that come with Visual Studio 2015 Community Edition.

You may want to consider an older (pre-2015) Mac if you really need it. Have you considered using standard VM engines as an alternative?

I wanted to be able to run as bare metal as possible, 32GB on this Mac and wanted to leverage that against multiple vm's

If you can find an older Mac (2012 or older), it may be worth testing Hyper-V.

not when i dropped almost $4K on a 5K iMac. Seems slightly problematic, to get base level functionality thats in old machines but not in a new one.

The CSM-BIOS layer is being deprecated in newer Macs after 2014 models. 2014s are excellent machines. Sierra is closing some doors, but opening others, for example Continuity.

Although I can't get you Hyper-V, I can at least give you the steps I followed to get my machine back in operation. Like others, I'm using a 2015 iMac with Windows 10 in bootcamp. I found out the hard way that even just installing visual studio 2013 with Windows Phone support would knock me out. I suspect the install process turns on Hyper-V automatically. Anyhow here's what I did:

1) Restore point - just before the problem happened. Didn't solve it.

2) Launch into safe mode using command prompt to disable Hyper-V. Actually it was already disabled (probably by step #1) but just in case you need to do this here are the commands:

C:\> dism /Online /Disable-Feature:Microsoft-Hyper-V-All

(per this link: http://www.poweronplatforms.com/enable-disable-hyper-v-windows-10-8/ )

3) But here is the gravy step - the windows boot record needs to be adjusted to force hypervisor off using bcdedit. I was actually booted into Safe mode (graphical with an admin command prompt) but I suspect it would work in the command line version too.

bcdedit {current} /set hypervisorlaunchtype off

(per this link: https://blogs.msdn.microsoft.com/virtual_pc_guy/2008/04/14/creating-a-no-hypervi sor-boot-entry/

At least you don't have to reinstall!

What's specific about Hyper-V that would cause it to fail when other virtualization products like Oracle Virtual Box work ? Just wondering if you came across some information while your were troubleshooting?

Well Hyper-V is using some sort of hardware technology that's right on the CPU whereas non-hyper-v apps are doing everything in software. The failure appears to be related to initial handshaking between the OS and UEFI on the Mac. As others mentioned, Windows is probably relying on the BIOS compatibility layer to kick things off properly when Hyper-V is turned on. Somehow Windows (once booted) has enough knowledge to say hey this CPU supports virtualization therefore Hyper-V *can* be turned on. But when going through the boot process, something is of course amiss.

It's either up to Windows to hack around the Mac UEFI, or Apple to re-introduce the BIOS compatibility layer. My guess is Apple won't budge and Windows will eventually move forward when other manufacturer's start using straight UEFI.

(but I'm kinda ignorant so don't trust me :-) )

According to the link below that Loner T had listed:

https://msdn.microsoft.com/virtualization/hyperv_on_windows/quick_start/walkthro ugh_compatibility

I have all the requirements:

There has to be a way to find out exactly what the problem is, I feel like we have just guessed that the problem is the bios.

Once Windows throws the error are there any logs to check to get more information ?

The derivation of these flags is erroneous on Late 2013 and later Mac models. Windows is looking at the CPU for VT-x information, which can be checked using

sysctl machdep.cpu.features

machdep.cpu.features: FPU VME DE PSE TSC MSR PAE MCE CX8 APIC SEP MTRR PGE MCA CMOV PAT PSE36 CLFSH DS ACPI MMX FXSR SSE SSE2 SS HTT TM PBE SSE3 PCLMULQDQ DTES64 MON DSCPL VMX SMX EST TM2 SSSE3 FMA CX16 TPR PDCM SSE4.1 SSE4.2 x2APIC MOVBE POPCNT AES PCID XSAVE OSXSAVE SEGLIM64 TSCTMR AVX1.0 RDRAND F16C

CSM-BIOS is still supported, even on Sierra, because a Mac upgraded from older OSX versions to Sierra still allows grand-fathered legacy BIOS installations of WXP, Vista, W7/W8.1/W10. And W10 can also be installed on Macs using legacy BIOS (I have it on 2012 preUEFI models so Audio will work correctly). BC Assistant enforces EFI on 2015 and later models using appropriate NVRAM settings used by the Installer.

As suggested earlier, use a VM engine, albeit being slow or buy a cheap PC. It is very unlikely that Apple will change the behavior, unless every consumer wants to run Hyper-V and the Mac sales get tied to just this feature.

For errors, I suggest starting with Event Viewer. I will look for logs on my 2012 MBP.

@Loner T, can you clarify what you mean by the following:

"The derivation of these flags is erroneous on Late 2013 and later Mac models. Windows is looking at the CPU for VT-x information, which can be checked using

"

Are you saying that the flags returned by executing

sysctl machdep.cpu.features should not be trusted on 2013 and later models?