flat assembler
Message board for the users of flat assembler.

Index > Windows > Why CPUID hypervisor flag is set?

Author
Thread Post new topic Reply to topic
CandyMan



Joined: 04 Sep 2009
Posts: 414
Location: film "CandyMan" directed through Bernard Rose OR Candy Shop
CandyMan 11 Aug 2021, 15:38
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).

_________________
smaller is better
Post 11 Aug 2021, 15:38
View user's profile Send private message Reply with quote
bitRAKE



Joined: 21 Jul 2003
Posts: 4071
Location: vpcmpistri
bitRAKE 11 Aug 2021, 19:23
AMD documentation states it as reserved, but read as zero. Obviously, the hypervisor controls what is returned for CPUID and can set it to any value.

This article suggests that the value is not well defined:
http://www.os2museum.com/wp/frequently-given-misleading-answers/

Maybe you could test from an EFI Shell to insure Windows is not doing something?

_________________
¯\(°_o)/¯ “languages are not safe - uses can be” Bjarne Stroustrup
Post 11 Aug 2021, 19:23
View user's profile Send private message Visit poster's website Reply with quote
sinsi



Joined: 10 Aug 2007
Posts: 794
Location: Adelaide
sinsi 11 Aug 2021, 21:06
If you have enabled Hyper-V in Windows, then even if you aren't using any VMs Windows runs as a special VM.
Quote:
with virtualization enabled, the host OS also runs on top of the Hyper-V virtualization layer, just as guest operating systems do.

https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/about/
Post 11 Aug 2021, 21:06
View user's profile Send private message Reply with quote
Feryno



Joined: 23 Mar 2005
Posts: 514
Location: Czech republic, Slovak republic
Feryno 20 Aug 2021, 05:11
then you can then ask hypervisor info by executing cpuid with input eax=40000000h and further
more info here:
https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/reference/tlfs
Post 20 Aug 2021, 05:11
View user's profile Send private message Visit poster's website ICQ Number Reply with quote
Display posts from previous:
Post new topic Reply to topic

Jump to:  


< Last Thread | Next Thread >
Forum Rules:
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum


Copyright © 1999-2025, Tomasz Grysztar. Also on GitHub, YouTube.

Website powered by rwasa.