Re: [Xen-users] xl cpuid masking howto

[Hans van Kranenburg <hans.van.kranenburg@xxxxxxxxxx>]

On 08/22/2016 04:30 PM, Hans van Kranenburg wrote:
> Hi Xen users,
> 
> Since I spent way too much time last week figuring out how to properly
> set the cpuid masks in my xen guests configuration files to be able to
> live migrate over slightly different types of hardware, I did a write up
> documenting the whole thing:
> 
> https://tech.mendix.com/linux/2016/08/18/xen-cpuid-masking/
> 
> I hope the text will save other people some time and headaches. Also, if
> I by accident wrote something that's blatantly incorrect, let me know.
> 
> I'm aware that there's work going on in this area now, so I explicitely
> mention that I used Xen 4.4.1 in this case.

I just made one change, which is not using:

   '0x00000001,0x00:ecx=x00xxxxxx0xxxxxxxxx00xxxxxxxxxxx',

but using this (without the 0x00):

   '0x00000001:ecx=x00xxxxxx0xxxxxxxxx00xxxxxxxxxxx',

The visible result in the cpuid -1r output is identical, but with the
0x00 in place this happens:

$ java -version
Error occurred during initialization of VM
Unknown x64 processor: SSE2 not supported

And without the 0x00:

$ java -version
java version "1.7.0_55"
Java(TM) SE Runtime Environment (build 1.7.0_55-b13)
Java HotSpot(TM) 64-Bit Server VM (build 24.55-b03, mixed mode)

And I have absolutely no clue why, but omitting the 0x00 for 1 makes
sense nonetheless, since it's redundant information. :)

Hans van Kranenburg

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