Comment 6 for bug 1748622

A little more digging:

Looking at the host_x86_cpu_class_init stack frame:

(gdb) print host_cpudef
$4 = {name = 0x0, level = 0, xlevel = 0, vendor = "GenuineIntel", family = 6, model = 42, stepping = 1, features = {0 <repeats 19 times>}, model_id = 0x0}

(gdb) print host_cpudef.model
$16 = 42

SandyBridge and SandyBridge-IBRS are model 42