RFR: 8250598: Hyper-V is detected in spite of running on host OS

[David Holmes]

On 27/07/2020 5:20 pm, Yasumasa Suenaga wrote:
> On 2020/07/27 16:09, David Holmes wrote:
>> On 27/07/2020 3:23 pm, Yasumasa Suenaga wrote:
>>> On 2020/07/27 14:21, Yasumasa Suenaga wrote:
>>>> Hi David,
>>>>
>>>> On 2020/07/27 14:02, David Holmes wrote:
>>>>>
>>>>>
>>>>> On 27/07/2020 2:24 pm, Yasumasa Suenaga wrote:
>>>>>> Hi all,
>>>>>>
>>>>>> Please review this change:
>>>>>>
>>>>>>    JBS: https://bugs.openjdk.java.net/browse/JDK-8250598
>>>>>>    webrev: 
>>>>>> http://cr.openjdk.java.net/~ysuenaga/JDK-8250598/webrev.00/
>>>>>>
>>>>>> When I got hs_err log on Windows, I saw "HyperV virtualization 
>>>>>> detected" in it in spite of running on host OS.
>>>>>>
>>>>>> Hypervisor detector has been introduced in JDK-8219241, but it has 
>>>>>> some problems as below:
>>>>>>
>>>>>>    - Hyper-V is detected on Windows in spite of running on host OS
>>>>>>    - Call CPUID with other than EAX = 40000000h (it is not 
>>>>>> described in the spec [1])
>>>>>
>>>>> That VMWare document is not a "spec" for anything other than 
>>>>> VMware. So this may work for VMWare:
>>>>>
>>>>>    a->movl(rax, 0x40000000);
>>>>>
>>>>> but may not work for all other HV environments - which is why the 
>>>>> original code checks a range of addresses within the reserved area. 
>>>>> See this related code for example:
>>>>>
>>>>> http://git.annexia.org/?p=virt-what.git;a=blob;f=virt-what-cpuid-helper.c;h=9c6cdb290105ca86868e2c7935ed42a55598b0f7;hb=HEAD 
>>>>>
>>>>>
>>>>>    71   /* Most hypervisors only have information in leaf 0x40000000.
>>>>>    72    *
>>>>>    73    * Some hypervisors have "Viridian [HyperV] extensions", 
>>>>> and those
>>>>>    74    * must appear in slot 0x40000000, but they will also have 
>>>>> the true
>>>>>    75    * hypervisor in a higher slot.
>>>>>
>>>>> You have to be able to check this on a range of HV's to ensure you 
>>>>> have not broken anything.
>>>>
>>>> Currently this feature supports VMware, Hyper-V, KVM, Xen.
>>>> We can distinguish them from CPUID with 40000000h. So we should not 
>>>> check other than 40000000h.
>>>>
>>>>     VMware: https://kb.vmware.com/s/article/1009458
>>>>    Hyper-V: 
>>>> https://docs.microsoft.com/virtualization/hyper-v-on-windows/reference/hyper-v-architecture 
>>>>
>>>
>>> Sorry, Hyper-V spec is here:
>>>
>>> https://docs.microsoft.com/virtualization/hyper-v-on-windows/reference/tlfs 
>>>
>>>
>>> In Windows Server 2019, you can see CPUID in 2.4.1 .
>>>
>>>
>>>>        KVM: https://www.kernel.org/doc/html/latest/virt/kvm/cpuid.html
>>>>        Xen: 
>>>> https://xenbits.xen.org/docs/unstable/hypercall/x86_32/include,public,arch-x86,cpuid.h.html 
>>>>
>>>>
>>>>
>>>>> Did you actually diagnose why the existing code mis-detects Hyper-V 
>>>>> under Windows?
>>>>
>>>> CPUID with EAX = 40000000h returns "Microsoft Hv" if Hyper-V is 
>>>> installed. I guess it is caused by Hyper-V architecture.
>>
>> But do we actually check the enabled bit:
>>
>> "Bit 31 returned in ECX is defined as Not Used, and will always return 
>> 0 from the physical CPU. A hypervisor conformant with the Microsoft 
>> hypervisor interface will set CPUID.1:ECX [bit 31] = 1 to indicate its 
>> presence to software."
>>
>> ?
> 
> CPUID with EAX = 40000000h would be handled in vCPU, so it is worth to 
> check bit 31.
> KVM document implies it.
> 
>    https://www.kernel.org/doc/html/latest/virt/kvm/cpuid.html

Let me try this again. This bug report was created because the hpervisor 
detection code is falsely reporting we are executing in hyper-v under 
Windows even when we are actually running a non-virtualized native OS. 
My question about the original is code is what part of it, exactly, is 
responsible for that false report?

Thanks,
David

> 
> Thanks,
> 
> Yasumasa
> 
> 
>> Thanks,
>> David
>> -----
>>
>>>> According to [1], root partition is as a host OS, so I guess JVM 
>>>> would detect which is running on Hyper-V even if it is running on 
>>>> host OS.
>>>>
>>>>
>>>> Thanks,
>>>>
>>>> Yasumasa
>>>>
>>>>
>>>> [1] 
>>>> https://docs.microsoft.com/ja-jp/virtualization/hyper-v-on-windows/reference/hyper-v-architecture 
>>>>
>>>>
>>>>
>>>>> David
>>>>> -----
>>>>>
>>>>>>    - Does not check CPUID hypervisor present bit [1]
>>>>>>    - Does not support x86 (32bit) platform
>>>>>>
>>>>>> I've tested this change on submit repo, and have checked output 
>>>>>> from VM.info jcmd on following environment:
>>>>>>
>>>>>>    - Windows x64 (host)
>>>>>>    - Windows x64 (Hyper-V guest)
>>>>>>    - Fedora32 x64 (Hyper-V guest)
>>>>>>    - 32 bit JDK on Fedora32 x64 (Hyper-V guest)
>>>>>>
>>>>>>
>>>>>> Thanks,
>>>>>>
>>>>>> Yasumasa
>>>>>>
>>>>>>
>>>>>> [1] https://kb.vmware.com/s/article/1009458