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CandyMan 11.08.2021, 17:31	Why CPUID hypervisor flag is set? (Miscellaneous) Post reply
	Does anyone know why the processor returns CPUID.00000001h.ECX = 0xFE9AE383 and the flag set (Bit 31: Running on a hypervisor) on a real CPU? (Windows OS, CPU = Intel Xeon ES-2680, family 6, model 62, stepping 4).

tkchia

11.08.2021, 18:29

@ CandyMan

Why CPUID hypervisor flag is set?

Post reply

Hello CandyMan,

> Does anyone know why the processor returns
> CPUID.00000001h.ECX = 0xFE9AE383 and the flag set
> (Bit 31: Running on a hypervisor) on a real CPU?
> (Windows OS, CPU = Intel Xeon ES-2680, family 6, model 62, stepping 4).

No idea. Perhaps some hypervisor is indeed installed by the Windows setup? Try calling cpuid leaf 0x40000000 ( https://sandpile.org/x86/cpuid.htm#level_4000_0000h ) and see what it says...

Thank you!

---
https://gitlab.com/tkchia · https://codeberg.org/tkchia · 😴 "MOV AX,0D500H+CMOS_REG_D+NMI"

Rugxulo

Usono,
11.08.2021, 22:31

@ tkchia

Why CPUID hypervisor flag is set?

Post reply

> > Does anyone know why the processor returns
> > CPUID.00000001h.ECX = 0xFE9AE383 and the flag set
> > (Bit 31: Running on a hypervisor) on a real CPU?
> > (Windows OS, CPU = Intel Xeon ES-2680, family 6, model 62, stepping 4).
>
> No idea. Perhaps some hypervisor is indeed installed by the Windows
> setup?

Is Hyper-V installed? Even WSL2 (Windows Subsystem for Linux) uses VT-X nowadays, last I heard. (But I've never used Windows 10.)

I actually think that causes (or used to cause) conflicts with other hypervisor software. And VirtualBox dropped support for cpus without hardware VT-X extensions sometime last year, IIRC. So, more or less, everyone is expected to have it available these days. (EDIT: Even this Chromebook [Celeron] has VT-X.)

alexfru USA, 12.08.2021, 09:35 @ CandyMan	Why CPUID hypervisor flag is set? Post reply
	> Does anyone know why the processor returns > CPUID.00000001h.ECX = 0xFE9AE383 and the flag set > (Bit 31: Running on a hypervisor) on a real CPU? > > (Windows OS, CPU = Intel Xeon ES-2680, family 6, model 62, stepping 4). Windows itself runs in a VM nowadays.

RayeR

CZ,
14.08.2021, 15:38

@ alexfru

Why CPUID hypervisor flag is set?

Post reply

> Windows itself runs in a VM nowadays.

Really Windows itself as VM client?
Older Win10 (that I have at work - frozen 2 years ago without updates) doesn't have HyperV yet so I guess it shouldn't run virtualized. I use Virtualbox for virtualization there and it had some conflict with old HyperV but it's probably solved. Current Win10 may use HyperV by default for WSL and other stuff, so if someone tell more detailed...

> CandyMan
Just run your code under DOS and see...

---
DOS gives me freedom to unlimited HW access.

alexfru

USA,
16.08.2021, 03:15

@ RayeR

Why CPUID hypervisor flag is set?

Post reply

> > Windows itself runs in a VM nowadays.
>
> Really Windows itself as VM client?

Ever since Hyper-V came out.

> Older Win10 (that I have at work - frozen 2 years ago without updates)
> doesn't have HyperV yet so I guess it shouldn't run virtualized. I use
> Virtualbox for virtualization there and it had some conflict with old
> HyperV but it's probably solved. Current Win10 may use HyperV by default
> for WSL and other stuff, so if someone tell more detailed...

I think, Hyper-V now provides some additional security features for Windows itself, not just runs other VMs.

RayeR

CZ,
16.08.2021, 03:29

@ alexfru

Why CPUID hypervisor flag is set?

Post reply

> I think, Hyper-V now provides some additional security features for Windows
> itself, not just runs other VMs.

And how the windows drivers are running? They must interact with real HW not virtualized ones. Are they run in Hyper-V domain so only userland part of windows runs virtualized? Or are there 2 kind of drivers - real HW ones and VM ones for virtualized windows?

---
DOS gives me freedom to unlimited HW access.

alexfru

USA,
16.08.2021, 07:20

@ RayeR

Why CPUID hypervisor flag is set?

Post reply

> > I think, Hyper-V now provides some additional security features for
> Windows
> > itself, not just runs other VMs.
>
> And how the windows drivers are running? They must interact with real HW
> not virtualized ones.

When we talk about the "root partition"/"host OS", I think they work as usual for the most part.

> Are they run in Hyper-V domain so only userland part
> of windows runs virtualized? Or are there 2 kind of drivers - real HW ones
> and VM ones for virtualized windows?

There are some drivers for Hyper-V-based devices in VMs.

Alex

Why CPUID hypervisor flag is set? (Miscellaneous)

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