On 08.01.2018 21:19, Jim Mattson wrote: > Even more trivially, what if the L2 VM is configured never to leave > VMX non-root operation? Then we never exit to userspace? Well we would make the PC point at the VMLAUNCH. Then exit to userspace. When returning from userspace, try to execute VMLAUNCH again, leading to an intercept and us going back into nested mode. A question would be, what happens to interrupts. They could be delivered, but it would look like the guest was not executed. (as we are pointing at the VMLAUNCH instruction). Not sure of this is a purely theoretical problem. But the "assigned devices" thing is a real difference to s390x. Assigning devices requires special SIE extensions we don't implement for vSIE. And there is no such thing as MMIO. And if there is one case where we need it (assigned devices) - even though we might find a way around it - it is very likely that there is more. -- Thanks, David / dhildenb
