Comment 27 for bug 1829555

I re-checked all that you and I found, lets write a List with all that we know if there are patterns.

Host (should not matter, but be rather new) - in my case B4.18 Q2.11

For new qemu I'm using Mitaka.
In this case being from https://launchpad.net/~ubuntu-cloud-archive/+archive/ubuntu/mitaka-staging
to get those libvirt/qemu with the MDS fixes which are still waiting to be released.

The check is like:
$ uname -r; cat /sys/devices/system/cpu/vulnerabilities/mds; cat /proc/cpuinfo | grep -e ^bug -e ^flags | grep md

An example result would look like
a) 4.4.0-148-generic
b) Mitigation: Clear CPU buffers; SMT Host state unknown
c) flags : [...] md_clear
d) bugs : cpu_meltdown spectre_v1 spectre_v2 spec_store_bypass l1tf mds

a) to verify the kernel level is as expected
b) to show what the kernel thinks about the Mitigation status
c) check the md_clear in cpu flags
d) show bugs the cpu is affected (not present on 3.13)

Only if all those above are ok we call it good, otherwise add a comment what fails

Test list:
lvl 1 kernel T3.13 / T4.4
lvl 2 kernel T3.13 / T4.4 / B4.15
Qemu T2.0 / M2.5

T LVL1 LVL2 Result
01 T3.13 / Q2.0 T3.13 ok
02 T3.13 / Q2.0 T4.4 ok
03 T3.13 / Q2.0 B4.15 full passthrough crashes, md-clear feature not passed
04 T3.13 / Q2.5 T3.13 ok
05 T3.13 / Q2.5 T4.4 ok
06 T3.13 / Q2.5 B4.15 ok
07 T4.4 / Q2.0 T3.13 shows not-affected, md-clear available
08 T4.4 / Q2.0 T4.4 shows not-affected, md-clear available
09 T4.4 / Q2.0 B4.15 shows not-affected, md-clear available
10 T4.4 / Q2.5 T3.13 ok
11 T4.4 / Q2.5 T4.4 ok
12 T4.4 / Q2.5 B4.15 ok

Of these testcases we have two fields of errors.
#03 : base Trusty with a rather new guest having issues
      Fix to that seems to be in the kernel as 3.13 -> 4.4 fixes it

#07-09: The qemu 2.0 in trusty seems to have issues if used with the HWE 4.4 kernel
        The fix to that seems to be in a newer qemu as 2.0 -> 2.5 fixes it