diff --git a/docs/Interference_Scenarios_for_an_ARM64_Linux_System.md b/docs/Interference_Scenarios_for_an_ARM64_Linux_System.md index 67ad900..dddc55f 100644 --- a/docs/Interference_Scenarios_for_an_ARM64_Linux_System.md +++ b/docs/Interference_Scenarios_for_an_ARM64_Linux_System.md @@ -472,6 +472,16 @@ This is perfectly fine from the perspective of containing user-space, however, s frequency execution of a large amount of code which can cause either direct or indirect interference. And such interference is not always detectable, depending on which component it might affect. +These means are usualy enabled in a mixed criticality scenario, when attempting to contain interference. +The choice of enabling them, despite the associated risk, might be driven by overall considerations about choosingthe lesser evil. +Of course one could attemtp to qualify them, but then it is necessary to consider the fact that in reality it is necessary to qualify them together with the user-space-provided policies they will enact. +Without being configured by user-space, neither SELinux nor cgroups are of any particular use. + +An alternative - possibly more costly - path could be to instead isolate more safety relevant loads from non safety relevant ones, introducing a second virtual machine, with an hypervisor underneath. +The caveat is that now the hypervisor can be a source of interference. And it is also necessary to have HW capable to support an EL2. +It can be an interesting alternative, though, if using a Type1 hypervisor (like Xen), because it is relatively simpler than trying to qualify the Linux code. + + ## Sources of Interference It is useful to model the most probable causes for spatial interference, even if not exhaustively.