Comment # 74 on bug 1112824 from Michiel Janssens

I've booted kernel-default with parameters spectre_v2=retpoline,generic

Now I have the same performance as kernel-vanilla without parameters.

4.19.5-1-default with spectre_v2=retpoline,generic:
/sys/devices/system/cpu/vulnerabilities/spectre_v2
Mitigation: Full generic retpoline, IBPB, IBRS_FW