[Xen-devel] Different CPU flags between Dom0 and DomU?

[Choonho Son <choonho.son@xxxxxxxxx>]

Hi all,

I have a machine with Intel Xeon E5-2630. Intel E5-series supports
AVX(Advanced Vector eXtension). And Xen Hypervisor 4.1 also supports
AVX feature.

/proc/cpuinfo shows the supported features:

- Bare-metal Linux (/proc/cpuinfo)
flags           : fpu vme de pse tsc msr pae mce cx8 apic 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
xtopology nonstop_tsc aperfmperf pni pclmulqdq dtes64 monitor ds_cpl
vmx smx est tm2 ssse3 cx16 xtpr pdcm dca sse4_1 sse4_2 x2apic popcnt
aes xsave avx lahf_lm ida arat xsaveopt pln pts dts tpr_shadow vnmi
flexpriority ept vpid

- Dom0 (/proc/cpuinfo)
flags           : fpu de tsc msr pae mce cx8 apic sep mca cmov pat
clflush acpi mmx fxsr sse sse2 ss ht syscall nx lm constant_tsc
rep_good nopl nonstop_tsc eagerfpu pni pclmulqdq monitor est ssse3
cx16 sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx
hypervisor lahf_lm ida arat xsaveopt pln pts dtherm

- DomU (/proc/cpuinfo)
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx rdtscp lm
constant_tsc pni ssse3 cx16 sse4_1 sse4_2 popcnt lahf_lm


[Questions]

1) Why CPU flags are different among bare-metal, dom0, and domU?
2) How can I use avx in DomU?
3) How CPU flags are delivered from Dom0(or Hypervisor) to DomU?

[reference]
http://blog.xen.org/index.php/2011/03/25/xen-4-1-releases/

Thanks,

Choonho Son

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