Comment 4 for bug 1755624

4.15.0-12.13-generic, from bionic-proposed, fixes this bug for me due to it containing this upstream commit:

1751342095f0d2b36fa8114d8e12c5688c455ac4

Relevant CPU model info from /proc/cpuinfo:

cpu family : 6
model : 78
model name : Intel(R) Core(TM) m5-6Y54 CPU @ 1.10GHz
stepping : 3
microcode : 0xc2

Model 78 corresponds to 0x4E in hex, which matches this in-kernel model:

#define INTEL_FAM6_SKYLAKE_MOBILE 0x4E

That's one of the models that was removed in the commit mentioned above.

I can also confirm that the flags field of cpuinfo contains "ibpb ibrs stibp".