Two different OS on different cores in same cluster with no EL2 enabled

Thanks a lot, Martin Weidmann . Got your point. For the isolation issue, technically it can be handled by some HW isolation mechanism implemented in the SOC, right?

Besides of the isolation and GIC issue, I am wondering if any other restriction which makes this impossible. If DSU (L3 cache, snoop, etc) is one of the restriction? 

Thanks.  

Thanks a lot, Martin Weidmann . Got your point. For the isolation issue, technically it can be handled by some HW isolation mechanism implemented in the SOC, right?

Besides of the isolation and GIC issue, I am wondering if any other restriction which makes this impossible. If DSU (L3 cache, snoop, etc) is one of the restriction? 

Thanks.  

SoC level isolation, such as system MPUs, would be tricky.  The issue is that that once the transaction leaves the processor, how are you going to know which core (and hence which OS) it came from?  Also, the shared in processor caches would be above the system MPU, so unaffected by SoC-level filtering.  Not saying you couldn't come up with a solution - but I suspect none would be as simple or well understood as using the existing EL2 controls.  Allows multiple different software stacks to run in isolated boxes is what EL2 is there for - what's the advantage of inventing a different mechanism?

The GIC was more of an example of a kind of issue.  You could go through the devices that need to be shared (GIC, power control, system timer....) and come up with solutions for each.  The question would be - why is that better than using a hypervisor of some form?  

Thanks a lot for your crystal clean explanations.  Martin Weidmann