On 2013-02-21 11:18, Jan Kiszka wrote: > On 2013-02-21 11:06, Gleb Natapov wrote: >> On Thu, Feb 21, 2013 at 10:43:57AM +0100, Jan Kiszka wrote: >>> On 2013-02-21 10:22, Gleb Natapov wrote: >>>> 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. >>> >>> Precisely this is the case if an IRQ for L1 arrived while we tried to >>> enter L2 and caused the cancellation above. >>> >> But during next entry the cancelled interrupt is transfered >> from architectural VCPU state to VM_ENTRY_INTR_INFO_FIELD by >> inject_pending_event()->vmx_inject_irq(), so at the point where >> enable_irq_window() is called the state is exactly the same no matter >> whether we canceled interrupt or not during previous entry attempt. What >> am I missing? > > Maybe that we normally either have an external IRQ pending in some IRQ > chip or in the VCPU architectural state, not both at the same time? By > transferring something that doesn't come from a virtual IRQ chip of L0 > (but from the one in L1) into the architectural state, we break this > assumption. > >> Oh may be I am missing that if we do not cancel interrupt >> then inject_pending_event() will skip >> if (vcpu->arch.interrupt.pending) >> .... > > If we do not cancel, we will not inject at all (due to missing > KVM_REQ_EVENT). > >> and will inject interrupt from APIC that caused cancellation of previous >> entry, but then this is a bug since this new interrupt will overwrite >> the one that is still in VM_ENTRY_INTR_INFO_FIELD from previous entry >> attempt and there may be another pending interrupt in APIC anyway that >> will cause enable_irq_window() too. > > Maybe the issue is that we do not properly simulate a VMEXIT on an > external interrupt during vmrun (like SVM does). Need to check for this > case again... static int vmx_interrupt_allowed(struct kvm_vcpu *vcpu) { if (is_guest_mode(vcpu) && nested_exit_on_intr(vcpu)) { struct vmcs12 *vmcs12 = get_vmcs12(vcpu); if (to_vmx(vcpu)->nested.nested_run_pending || (vmcs12->idt_vectoring_info_field & VECTORING_INFO_VALID_MASK)) return 0; nested_vmx_vmexit(vcpu); vmcs12->vm_exit_reason = EXIT_REASON_EXTERNAL_INTERRUPT; vmcs12->vm_exit_intr_info = 0; ... I do not understand ATM why we refuse to simulate a vmexit due to an external interrupt when we are about to run L2 or have something in idt_vectoring_info_field. The external interrupt would not overwrite idt_vectoring_info_field but should end up in vm_exit_intr_info. 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
