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Re: [Xen-devel] Changing the CPUID hypervisor string for HVM DomU

On 03/28/2016 05:34 AM, Fanny Dwargee wrote:

I'm currently using Xen v4.6.1 compiled from sources on Linux Debian Jessie and I would like to change the CPUID hypervisor vendor string when queried from a HVM DomU (Windows7 SP1 64 bits).

According to http://www.sandpile.org/x86/cpuid.htm#level_4000_0000h this information is queried via EAX=0x40000000 and returned on EBX-ECX-EDX registers

The current vendor string is "XenVMMXenVMM" and I want to replace it by the string "JUSTATEST" so I changed my DomU configuration to:

    cpuid = [

    hap  = 1
    acpi = 1
    altp2mhvm = 1

but unfortunately the guest still shows "XenVMMXenVMM" as the hypervisor string.

After looking for that string in the Xen sources it seems to be harcoded in many places:

  * xen-4.6.1/docs/misc/pvrdtscp.c
  * xen-4.6.1/tools/firmware/seabios-dir-remote/src/fw/xen.c
  * xen-4.6.1/tools/firmware/hvmloader/hvmloader.c
  * xen-4.6.1/tools/misc/xen-detect.c
  * xen-4.6.1/unmodified_drivers/linux-2.6/platform-pci/platform-pci.c
  * xen-4.6.1/xen/include/public/arch-x86/cpuid.h
  * xen-4.6.1/extras/mini-os/include/xen/arch-x86/cpuid.h
  * xen-4.6.1/dist/install/usr/local/include/xen/arch-x86/cpuid.h

...so I'm afraid I will be unable to change it.

Any ideas or patches?

Thanks in advance

You can't change hypervisor signature (or most values in hypervisor leaves). See man page for xl.conf syntax ('cpuid' option) or libxc/xc_cpuid_x86.c:xc_cpuid_policy().


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