VT-x Support on iMac 27" (mid2010 - v11,3) - Docker for Mac

I have installed Docker for Mac which complain about my CPU VT-x support...

When I do :

sysctl kern.hv_support

it return :

kern.hv_support: 0

( https://developer.apple.com/reference/hypervisor )

I don't understand, my CPU is an Intel Core i7 870 with VT-x EPT support ( http://ark.intel.com/products/41315 ) :

sysctl -a | grep machdep.cpu.brand_string

Give me :

machdep.cpu.brand_string: Intel(R) Core(TM) i7 CPU 870 @ 2.93GHz

When I do :

sysctl -a | grep machdep.cpu.features

I have :

machdep.cpu.features: FPU VME DE PSE TSC MSR PAE MCE CX8 APIC SEP MTRR PGE MCA CMOV PAT PSE36 CLFSH DS ACPI MMX FXSR SSE SSE2 SS HTT TM PBE SSE3 DTES64 MON DSCPL VMX SMX EST TM2 SSSE3 CX16 TPR PDCM SSE4.1 SSE4.2 POPCNT

vmx

How can I enable VT-x support ?