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

[Yasumasa Suenaga]

Hi Matthias, David,

On 2020/08/12 21:12, David Holmes wrote:
> 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/

I understand that if the process runs on Xen on other hypervisor (e.g. KVM), information for Xen would be set between 0x40000100 and 0x40010000.
Ok, I will not remove the loop in new webrev, and will add comment about it.


>> 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.)

This value would be used in hs_err and VM.info dcmd, so we can determine it when it is needed.
However the change would be bigger, and it is not the original scope. Can we fix them at the same time?


Thanks,

Yasumasa


> 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.
>>>
>>