Re: [Xen-users] cpuid masking on Xen 4.1

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Fri, 11 Mar 2016, Charles Koprowski wrote:
> Hi,
> 
> 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...

Do you know where's this message coming from? set_cpuidmask doesn't have 
any message with this text in current versions.

Also, could you try with a newer version of Xen? Xen 4.1 has been 
unsupported for a long time now.

> So here are my questions :
> 
> Do all CPUs support CPUID masking ? In my case I'm trying on Intel
> Xeon E7-4850 v3

I'm not really familiar with with cpuid leveling, but I think there's 
indeed something wrong. I would expect that having cpu_has_cpuid_faulting 
means we would do the masking somewhere else (in the fault handler), but I 
cannot find any usages of opt_cpuid_mask_* anywhere outside of the intel 
and amd cpu initialization files.

I'm adding Andrew to the Cc, he has done quite a lot of work regarding 
cpuid, so he might know were the issue is.

Roger.

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