@olivierlambert Thanks. I tried that right now, booting with mitigations=off and saw no improvements unfortunately.

Before:

[09:06 VIRTUAL33 ~]# grep . /sys/devices/system/cpu/vulnerabilities/* /sys/devices/system/cpu/vulnerabilities/itlb_multihit:Not affected /sys/devices/system/cpu/vulnerabilities/l1tf:Not affected /sys/devices/system/cpu/vulnerabilities/mds:Not affected /sys/devices/system/cpu/vulnerabilities/meltdown:Not affected /sys/devices/system/cpu/vulnerabilities/spec_store_bypass:Vulnerable /sys/devices/system/cpu/vulnerabilities/spectre_v1:Mitigation: usercopy/swapgs barriers and __user pointer sanitization /sys/devices/system/cpu/vulnerabilities/spectre_v2:Mitigation: Full AMD retpoline, IBPB: conditional, STIBP: disabled, RSB filling /sys/devices/system/cpu/vulnerabilities/srbds:Not affected /sys/devices/system/cpu/vulnerabilities/tsx_async_abort:Not affected

After:

[12:18 VIRTUAL33 ~]# grep . /sys/devices/system/cpu/vulnerabilities/* /sys/devices/system/cpu/vulnerabilities/l1tf:Not affected /sys/devices/system/cpu/vulnerabilities/meltdown:Not affected /sys/devices/system/cpu/vulnerabilities/spec_store_bypass:Vulnerable /sys/devices/system/cpu/vulnerabilities/spectre_v1:Mitigation: __user pointer sanitization /sys/devices/system/cpu/vulnerabilities/spectre_v2:Mitigation: Full AMD retpoline, IBPB: conditional, STIBP: disabled, RSB filling

I also encountered this problem.
If you are using Debian you can use pre-packaged XO from sources https://github.com/mathiswolff/xen-orchestra