On Wed, Feb 20, 2013 at 06:50:50PM +0100, Jan Kiszka wrote: > On 2013-02-20 18:24, Jan Kiszka wrote: > > On 2013-02-20 18:01, Gleb Natapov wrote: > >> On Wed, Feb 20, 2013 at 03:37:51PM +0100, Jan Kiszka wrote: > >>> On 2013-02-20 15:14, Nadav Har'El wrote: > >>>> Hi, > >>>> > >>>> By the way, if you haven't seen my description of why the current code > >>>> did what it did, take a look at > >>>> http://www.mail-archive.com/kvm@xxxxxxxxxxxxxxx/msg54478.html > >>>> Another description might also come in handy: > >>>> http://www.mail-archive.com/kvm@xxxxxxxxxxxxxxx/msg54476.html > >>>> > >>>> On Wed, Feb 20, 2013, Jan Kiszka wrote about "[PATCH] KVM: nVMX: Rework event injection and recovery": > >>>>> This aligns VMX more with SVM regarding event injection and recovery for > >>>>> nested guests. The changes allow to inject interrupts directly from L0 > >>>>> to L2. > >>>>> > >>>>> One difference to SVM is that we always transfer the pending event > >>>>> injection into the architectural state of the VCPU and then drop it from > >>>>> there if it turns out that we left L2 to enter L1. > >>>> > >>>> Last time I checked, if I'm remembering correctly, the nested SVM code did > >>>> something a bit different: After the exit from L2 to L1 and unnecessarily > >>>> queuing the pending interrupt for injection, it skipped one entry into L1, > >>>> and as usual after the entry the interrupt queue is cleared so next time > >>>> around, when L1 one is really entered, the wrong injection is not attempted. > >>>> > >>>>> VMX and SVM are now identical in how they recover event injections from > >>>>> unperformed vmlaunch/vmresume: We detect that VM_ENTRY_INTR_INFO_FIELD > >>>>> still contains a valid event and, if yes, transfer the content into L1's > >>>>> idt_vectoring_info_field. > >>>> > >>>>> To avoid that we incorrectly leak an event into the architectural VCPU > >>>>> state that L1 wants to inject, we skip cancellation on nested run. > >>>> > >>>> I didn't understand this last point. > >>> > >>> - prepare_vmcs02 sets event to be injected into L2 > >>> - while trying to enter L2, a cancel condition is met > >>> - we call vmx_cancel_interrupts but should now avoid filling L1's event > >>> into the arch event queues - it's kept in vmcs12 > >>> > >> But what if we put it in arch event queue? It will be reinjected during > >> next entry attempt, so nothing bad happens and we have one less if() to explain, > >> or do I miss something terrible that will happen? > > > > I started without that if but ran into troubles with KVM-on-KVM (L1 > > locks up). Let me dig out the instrumentation and check the event flow > > again. > > OK, got it again: If we transfer an IRQ that L1 wants to send to L2 into > the architectural VCPU state, we will also trigger enable_irq_window. > And that raises KVM_REQ_IMMEDIATE_EXIT again as it thinks L0 wants > inject. That will send us into an endless loop. > Why would we trigger enable_irq_window()? enable_irq_window() triggers only if interrupt is pending in one of irq chips, not in architectural VCPU state. > Not sure if we can and should handle this scenario in enable_irq_window > in a nicer way. Open for suggestions. > > Jan > > -- > Siemens AG, Corporate Technology, CT RTC ITP SDP-DE > Corporate Competence Center Embedded Linux -- Gleb. -- 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
