[Xen-users] Problems with CPUID feature masking

[Jarno Elonen <elonen@xxxxxx>]

Hi,

I'm having trouble getting cpuid limit functionality in domain config
working and would appreciate any help.

My goal is to get live migration working between two different
generation Intel CPUs (Core2 Quad and i7).
The test domu is running paravirtualized Linux 3.2.0-2-amd64 on Debian
Wheezy. Dom0 runs XEN hypervisor 4.1.3~rc1+hg-20120614.a9c0a89c08f2-4.

On the i7 dom0, the linux 'cpuid' command returns (among others) a
line like this:
00000001 000206a7 00100800 179ae3bf bfebfbff

To limit the cpu features, I've added this to the domu config file...

cpuid = [ '0:eax=0x3,ebx=0x0,ecx=0x0,edx=0x0',
          '1:ecx=0x0000e3bd,edx=0xbfebfbff'
          '4:eax=0x3,ebx=0x0,ecx=0x0,edx=0x0',
          '0x80000000:eax=0x3,ebx=0x0,ecx=0x0,edx=0x0']

...but when I start the virtual machine and run the 'cpuid' command
there, it returns the same exact cpuid id as on dom0. When I try to
migrate it from i7 to Core2, kernel panics immediately after the
migration. The other direction works perfectly. I've enabled some kind
of CPUID limiting option from BIOS, just in case that's necessary.

Documentation of this feature is pretty scarce. Is it even supposed to
work on PV (or only on HVM)?

- Jarno

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