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. 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 -- 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
