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[Xen-users] cpuid masking on Xen 4.1

  • To: xen-users@xxxxxxxxxxxxx
  • From: Charles Koprowski <cko@xxxxxxxxxxx>
  • Date: Fri, 11 Mar 2016 15:27:13 +0100
  • Delivery-date: Fri, 11 Mar 2016 14:29:10 +0000
  • List-id: Xen user discussion <xen-users.lists.xen.org>


I'm trying to use cpuid masking on dom0 by passing cpuid_mask_ecx,
cpuid_mask_edx, cpuid_mask_ext_ecx and cpuid_mask_ext_edx options to
Xen command line.

Unfortunately, it seems that masks are not applied by Xen at boot
time. The output of the cpuid command and "cat /proc/cpuinfo" remains
the same as if I wouldn't pass any cpuid_mask_* options.

So I tried to debug the problem by recompiling Xen. Adding some printk
debug log to xen/arch/x86/cpu/intel.c showed  that set_cpuidmask()
isn't called during CPU init because cpu_has_cpuid_faulting equals 1
in my case.

Forcing set_cpuidmask() to be executed just prints out "(XEN) Cannot
set CPU feature mask on CPU#" messages...

So here are my questions :

Do all CPUs support CPUID masking ? In my case I'm trying on Intel
Xeon E7-4850 v3

If not, how can I know if a particular CPU supports it or not ?

Thanks !


Charles Koprowski

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