libvirt users - Feb 2015 - Re: CPU model and missing AES-NI extension

Hi,
today I tried to configure a guest using Virt-Manager and used the "copy
host cpu configuration" option which resultet in a "Sandy Bridge"
model.
What I noticed is that for example the "aes" extension is not
available
in the guest even though it is available on the host cpu.

This is what the host cpu looks like:

model name	: Intel(R) Xeon(R) CPU E5-2650 v3 @ 2.30GHz
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx
pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl
xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor
ds_cpl vmx smx est tm2 ssse3 fma cx16 xtpr pdcm pcid dca sse4_1 sse4_2
x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm
abm ida arat epb xsaveopt pln pts dtherm tpr_shadow vnmi flexpriority
ept vpid fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid

And this is what I get in the guest:

model name	: Intel Xeon E312xx (Sandy Bridge)
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
pat pse36 clflush mmx fxsr sse sse2 ss syscall nx pdpe1gb lm
constant_tsc pni ssse3 cx16 sse4_1 sse4_2 popcnt lahf_lm abm

Is there a way to get closer to the hardware and get as many of the host
features in the guest as possible? I never intend to do anything like
live-migration with this guest so compatibility for that case is not a
concern.

Regards,
  Dennis

On 04.02.2015 22:32, Dennis Jacobfeuerborn wrote:
> Hi,
> today I tried to configure a guest using Virt-Manager and used the
"copy
> host cpu configuration" option which resultet in a "Sandy
Bridge" model.
> What I noticed is that for example the "aes" extension is not
available
> in the guest even though it is available on the host cpu.
> 
> This is what the host cpu looks like:
> 
> model name	: Intel(R) Xeon(R) CPU E5-2650 v3 @ 2.30GHz
> flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
> pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx
> pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl
> xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor
> ds_cpl vmx smx est tm2 ssse3 fma cx16 xtpr pdcm pcid dca sse4_1 sse4_2
> x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm
> abm ida arat epb xsaveopt pln pts dtherm tpr_shadow vnmi flexpriority
> ept vpid fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid
> 
> And this is what I get in the guest:
> 
> model name	: Intel Xeon E312xx (Sandy Bridge)
> flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
> pat pse36 clflush mmx fxsr sse sse2 ss syscall nx pdpe1gb lm
> constant_tsc pni ssse3 cx16 sse4_1 sse4_2 popcnt lahf_lm abm
> 
> Is there a way to get closer to the hardware and get as many of the host
> features in the guest as possible? I never intend to do anything like
> live-migration with this guest so compatibility for that case is not a
> concern.
> 
I think this is XML snippet you're aiming for:

  <cpu mode='host-model'>
    <model fallback='allow'/>
  </cpu>


Michal

On 05.02.2015 13:00, Michal Privoznik wrote:
> On 04.02.2015 22:32, Dennis Jacobfeuerborn wrote:
>> Hi,
>> today I tried to configure a guest using Virt-Manager and used the
"copy
>> host cpu configuration" option which resultet in a "Sandy
Bridge" model.
>> What I noticed is that for example the "aes" extension is not
available
>> in the guest even though it is available on the host cpu.
>>
>> This is what the host cpu looks like:
>>
>> model name	: Intel(R) Xeon(R) CPU E5-2650 v3 @ 2.30GHz
>> flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
>> pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx
>> pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl
>> xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor
>> ds_cpl vmx smx est tm2 ssse3 fma cx16 xtpr pdcm pcid dca sse4_1 sse4_2
>> x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand
lahf_lm
>> abm ida arat epb xsaveopt pln pts dtherm tpr_shadow vnmi flexpriority
>> ept vpid fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid
>>
>> And this is what I get in the guest:
>>
>> model name	: Intel Xeon E312xx (Sandy Bridge)
>> flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
>> pat pse36 clflush mmx fxsr sse sse2 ss syscall nx pdpe1gb lm
>> constant_tsc pni ssse3 cx16 sse4_1 sse4_2 popcnt lahf_lm abm
>>
>> Is there a way to get closer to the hardware and get as many of the
host
>> features in the guest as possible? I never intend to do anything like
>> live-migration with this guest so compatibility for that case is not a
>> concern.
>>
> 
> I think this is XML snippet you're aiming for:
> 
>   <cpu mode='host-model'>
>     <model fallback='allow'/>
>   </cpu>
Hm, according to the documentation mode='host-model' should not be used?

"Beware, due to the way libvirt detects host CPU and due to the fact
libvirt does not talk to QEMU/KVM when creating the CPU model, CPU
configuration created using host-model may not work as expected. The
guest CPU may differ from the configuration and it may also confuse
guest OS by using a combination of CPU features and other parameters
(such as CPUID level) that don't work. Until these issues are fixed,
it's a good idea to avoid using host-model and use custom mode with just
the CPU model from host capabilities XML."

Regards,
 Dennis