Re: [Xen-users] CPUID DomU configuration not working

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

On Fri, 18 Mar 2016, Fanny Dwargee wrote:
> Hi,
> I'm trying to remove the VMX feature from the CPUID responses (bit 5 returned 
> on ecx register) setting the cpuid DomU configuration for a HVM Windows7.
> 
> Unfortunately using the CPUID instruction from inside the guest does still 
> shows the VMX bit as enabled.
> 
> No error is visible on logs nor xl dmesg. Xen is v4.6.1 compiled from source.
> 
> DomU configuration follows:
>       name = "win7-sp1-x64-2"
> 
> firmware_override = "/usr/local/lib/xen/boot/hvmloader"
> 
> builder='hvm'
> vcpus = 1
> maxcpus = 1
> 
> cpuid = [ '0x1:ecx=xxxxxxxxxxxxxxxxxxxxxxxxxx0xxxxx' ]
> 
> hap  = 1
> acpi = 1
> 
> on_poweroff = 'destroy'
> on_reboot   = 'restart'
> on_crash    = 'destroy'
> 
> vif = [ 'type=ioemu,model=e1000 ]
> disk = [ 'phy:/dev/vms/win7-sp1-x64-2,hda,w', 
> 'file:/opt/iso/win7.iso,hdc:cdrom,r' ]
> 
> boot="cd"
> 
> serial = 'pty'
> usb = 1
> usbdevice = 'tablet'
> #altp2mhvm = 1
> keymap = 'es'
> vga = 'stdvga'
> videoram = 16 

Are you sure this is all you have in your domain configuration file? The 
VMX bit should only be enabled if you have nestedhvm=1 in your config file 
AFAIK. Here is for example a configuration file for one of my HVM guests:

memory=512
vcpus=1
name="freebsd"
builder="hvm"
disk = [
 'phy:/dev/zvol/tank/freebsd,hda,rw,script=block',
]
vif = [
 'mac=00:16:3E:74:3d:76,bridge=bridge0',
]
serial='pty'

And the relevant output of cpuid:

Feature flags set 2 (CPUID.01H:ECX): fff83203:
SSE3     SSE3 extensions
PCLMULDQ PCLMULDQ instruction
SSSE3    Supplemental Streaming SIMD Extension 3
FMA      Fused Multiply-Add
CX16     CMPXCHG16B
SSE4.1   Streaming SIMD Extension 4.1
SSE4.2   Streaming SIMD Extension 4.2
x2APIC   Extended xAPIC support
MOVBE    MOVBE instruction
POPCNT   POPCNT instruction
TSC-Deadline
AESNI    AES Instruction set
XSAVE    XSAVE/XSTOR states
OSXSAVE  OS-enabled extended state managerment
AVX      AVX extensions
F16C     Half-precision conversions
RDRAND   RDRAND Instruction
31 - unknown feature 

As you can see bit 5 (VMX) is not enabled at all (and I'm not using any 
kind of CPUID masking in the config file).

How do you know that the VMX bit is set inside of the guest?

Roger.

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