On a host that is booted with the following command line, certain cpu flags disappear in xen-4.9 and later:
(XEN) Command line: loglvl=all guest_loglvl=all console=com1 com1=57600 cpuid=ibrsb,stibp,ibpb,ssbd spec-ctrl=ibrs,ibpb,ssbd,bti-thunk=retpoline xpti=yes On my test system the difference in dom0s /proc/cpuinfo is like that: --- xen-dom0-4.8-spectre.txt +++ xen-dom0-4.12-spectre.txt -arat -arch_perfmon -dtherm -epb -ida +ss The concern is that a domU started on a xen-4.8 or earlier host, which is then migrated to xen-4.9 or later may miss these cpu flags at runtime. Is the loss of cpuflags intentional? I just noticed that at least in staging a boot with "no-ibrsb no-stibp no-ibpb no-ssbd spec-ctrl=no-xen,rsb=no xpti=no" does still not show these flags in dom0. Olaf
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