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

[David Holmes]

On 12/08/2020 8:51 pm, Baesken, Matthias wrote:
> Hi Yasumasa ,  I'm more or less fine with the change .
> But still not fully convinced  that removing  the iteration is a good thing .
> 
> http://cr.openjdk.java.net/~ysuenaga/JDK-8250598/webrev.01/src/hotspot/cpu/x86/vm_version_x86.cpp.frames.html
> 
> 1827   for (base = 0x40000000; base < 0x40010000; base += 0x100) {
> 1828     check_virt_cpuid(base, registers);
> 
> I think just checking  "0x40000000" should work in most cases but if I remember correctly sometimes it was not enough .
> See also  some references about Xen/KVM :
> 
> https://lists.linuxfoundation.org/pipermail/virtualization/2012-May/019974.html
> 
> "If compat mode for another h/v is enabled then those leaves will appear
> at 0x40000000 and Xen's will be bumped up, so a fully Xen aware set of
> drivers (or detection routine, etc) should check at 0x100 intervals
> until 0x40010000 "
> 
> and
> 
> https://lore.kernel.org/patchwork/patch/394371/
> 
> 
> 
> And not so happy about the WMI  usage (called in early JVM startup) :
> 
> http://cr.openjdk.java.net/~ysuenaga/JDK-8250598/webrev.01/src/hotspot/os_cpu/windows_x86/vm_version_windows_x86.cpp.frames.html
> 
> bool VM_Version::is_in_VM() { ... }
>   ...
> }
> 
>   But if noone else complains about it, I guess it's okay .

I haven't reviewed this because I don't understand any of the code. But 
all that extra stuff during VM initialization doesn't look good to me. 
We do not want to pay a startup penalty just because we want a more 
accurate hypervisor listing in an error report!

Can we not determine this only if needed? (Granted doing all this stuff 
during crash reporting may also be an issue.)

David
-----

> 
> Best regards, Matthias
> 
> 
>> PING: Could you review this change?
>>
>>    JBS: https://bugs.openjdk.java.net/browse/JDK-8250598
>>    webrev: http://cr.openjdk.java.net/~ysuenaga/JDK-8250598/webrev.01/
>>
>> Build change has been reviewed by Erik.
>>
>