On Sat, Sep 15, 2012, Steven wrote about "Guest mode question": > Hi, > I have a question about vm execution in the guest mode. Suppose I have > two VMs on a machine. > Is it possible that both VMs are in the guest mode? Like this > vm1 enters guest mode > vm2 enters guest mode > // at this point, two VMs are in guest mode > > Or the hypervisor will first force one VM to vmexit before the second > VM enters the guest mode? Your description, of a *VM* being in guest mode, makes it sound like you're describing *nested* virtualization, i.e., running another hypervisor (like KVM) as the guest of the parent KVM. If this is what you actually meant, then, yes, indeed, several VMs may be in guest mode because they are each running a nested guest (aka an L2, a guest of a guest). But if you didn't ask about nested virtualization, but rather normal, single-level, virtualization, there's a different answer: It is the CPU thread (one core, or even one hyperthread), *not* the VM, which can be in root or guest mode. It is in root mode when the hypervisor runs, and in guest mode when a specific guest (VM) runs. One CPU thread can only run one code at a time, so of course it cannot be running two VMs at the same time - if it is running VM B now, it's because VM A is not running now. Of course, if you have a muticore machine, both A and B might be running, on two separate cores. In that case, both cores (not VMs) may be in guest mode concurrently. -- Nadav Har'El | Sunday, Sep 16 2012, 29 Elul 5772 nyh@xxxxxxxxxxxxxxxxxxx |----------------------------------------- Phone +972-523-790466, ICQ 13349191 |Does replacing myself with a shell-script http://nadav.harel.org.il |make me impressive or insignificant? -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
