RE: [Xen-devel] [PATCH]: Add support for Intel CPUID Feature mask in Xen

["Ian Pratt" <Ian.Pratt@xxxxxxxxxxxxx>]

> Hi, all
> Some Latest Intel CPU models (CPUID.1.EAX >= 0x00010674) support cupid
> mask features. Cpuid feature mask is used to limit the feature flags
> reported by CPUID.1.EDX:ECX.
> 
> This small patch adds CPUID feature mask support in XEN by adding boot
> options in Grub entry as below example:
> kernel /boot/xen.gz com1=115200,8n1 console=com1 cpuid_mask_ecx =
> 0xFFFF7FFF cpuid_mask_edx = 0xFFFFFFFC
> 
> For detailed usage information, please refer to the attached document:
> cupid_feature_mask.txt.

It's good to see this feature enabled, but it would be a lot more user
friendly if the patch took a cpu family and model number and then
'flattened' the cpuid back to the specification of that CPU. We don't
need to go back very far (certainly not pre-VT), and I'd be happy if we
just did all core2 (and newer) CPUs.

Also, is there a magic MSR to change the CPU family/model number
reported? It would make sense to do this too.

At what point does the CPU masking occur? Ideally we'd do it just before
starting dom0. [Actually, we might want to be able to invoke it from
libxc in future too]

Ian  

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