On Thu, Jul 03, 2014 at 01:15:26AM -0400, Bandan Das wrote: >Jan Kiszka <jan.kiszka@xxxxxxxxxxx> writes: > >> On 2014-07-02 08:54, Wanpeng Li wrote: >>> This patch fix bug https://bugzilla.kernel.org/show_bug.cgi?id=72381 >>> >>> If we didn't inject a still-pending event to L1 since nested_run_pending, >>> KVM_REQ_EVENT should be requested after the vmexit in order to inject the >>> event to L1. However, current log blindly request a KVM_REQ_EVENT even if >>> there is no still-pending event to L1 which blocked by nested_run_pending. >>> There is a race which lead to an interrupt will be injected to L2 which >>> belong to L1 if L0 send an interrupt to L1 during this window. >>> >>> VCPU0 another thread >>> >>> L1 intr not blocked on L2 first entry >>> vmx_vcpu_run req event >>> kvm check request req event >>> check_nested_events don't have any intr >>> not nested exit >>> intr occur (8254, lapic timer etc) >>> inject_pending_event now have intr >>> inject interrupt >>> >>> This patch fix this race by introduced a l1_events_blocked field in nested_vmx >>> which indicates there is still-pending event which blocked by nested_run_pending, >>> and smart request a KVM_REQ_EVENT if there is a still-pending event which blocked >>> by nested_run_pending. >> >> There are more, unrelated reasons why KVM_REQ_EVENT could be set. Why >> aren't those able to trigger this scenario? >> >> In any case, unconditionally setting KVM_REQ_EVENT seems strange and >> should be changed. > > >Ugh! I think I am hitting another one but this one's probably because >we are not setting KVM_REQ_EVENT for something we should. > >Before this patch, I was able to hit this bug everytime with >"modprobe kvm_intel ept=0 nested=1 enable_shadow_vmcs=0" and then booting >L2. I can verify that I was indeed hitting the race in inject_pending_event. > >After this patch, I believe I am hitting another bug - this happens >after I boot L2, as above, and then start a Linux kernel compilation >and then wait and watch :) It's a pain to debug because this happens >almost once in three times; it never happens if I run with ept=1, however, >I think that's only because the test completes sooner. But I can confirm >that I don't see it if I always set REQ_EVENT if nested_run_pending is set instead of >the approach this patch takes. >(Any debug hints help appreciated!) > >So, I am not sure if this is the right fix. Rather, I think the safer thing >to do is to have the interrupt pending check for injection into L1 at >the "same site" as the call to kvm_queue_interrupt() just like we had before >commit b6b8a1451fc40412c57d1. Is there any advantage to having all the >nested events checks together ? > How about revert commit b6b8a1451 and try if the bug which you mentioned is still there? Regards, Wanpeng Li >PS - Actually, a much easier fix (or rather hack) is to return 1 in >vmx_interrupt_allowed() (as I mentioned elsewhere) only if >!is_guest_mode(vcpu) That way, the pending interrupt interrupt >can be taken care of correctly during the next vmexit. > >Bandan > >> Jan >> >>> >>> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxxxxxx> >>> --- >>> arch/x86/kvm/vmx.c | 20 +++++++++++++++----- >>> 1 file changed, 15 insertions(+), 5 deletions(-) >>> >>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >>> index f4e5aed..fe69c49 100644 >>> --- a/arch/x86/kvm/vmx.c >>> +++ b/arch/x86/kvm/vmx.c >>> @@ -372,6 +372,7 @@ struct nested_vmx { >>> u64 vmcs01_tsc_offset; >>> /* L2 must run next, and mustn't decide to exit to L1. */ >>> bool nested_run_pending; >>> + bool l1_events_blocked; >>> /* >>> * Guest pages referred to in vmcs02 with host-physical pointers, so >>> * we must keep them pinned while L2 runs. >>> @@ -7380,8 +7381,10 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu) >>> * we did not inject a still-pending event to L1 now because of >>> * nested_run_pending, we need to re-enable this bit. >>> */ >>> - if (vmx->nested.nested_run_pending) >>> + if (to_vmx(vcpu)->nested.l1_events_blocked) { >>> + to_vmx(vcpu)->nested.l1_events_blocked = false; >>> kvm_make_request(KVM_REQ_EVENT, vcpu); >>> + } >>> >>> vmx->nested.nested_run_pending = 0; >>> >>> @@ -8197,15 +8200,20 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu, bool external_intr) >>> >>> if (nested_cpu_has_preemption_timer(get_vmcs12(vcpu)) && >>> vmx->nested.preemption_timer_expired) { >>> - if (vmx->nested.nested_run_pending) >>> + if (vmx->nested.nested_run_pending) { >>> + vmx->nested.l1_events_blocked = true; >>> return -EBUSY; >>> + } >>> nested_vmx_vmexit(vcpu, EXIT_REASON_PREEMPTION_TIMER, 0, 0); >>> return 0; >>> } >>> >>> if (vcpu->arch.nmi_pending && nested_exit_on_nmi(vcpu)) { >>> - if (vmx->nested.nested_run_pending || >>> - vcpu->arch.interrupt.pending) >>> + if (vmx->nested.nested_run_pending) { >>> + vmx->nested.l1_events_blocked = true; >>> + return -EBUSY; >>> + } >>> + if (vcpu->arch.interrupt.pending) >>> return -EBUSY; >>> nested_vmx_vmexit(vcpu, EXIT_REASON_EXCEPTION_NMI, >>> NMI_VECTOR | INTR_TYPE_NMI_INTR | >>> @@ -8221,8 +8229,10 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu, bool external_intr) >>> >>> if ((kvm_cpu_has_interrupt(vcpu) || external_intr) && >>> nested_exit_on_intr(vcpu)) { >>> - if (vmx->nested.nested_run_pending) >>> + if (vmx->nested.nested_run_pending) { >>> + vmx->nested.l1_events_blocked = true; >>> return -EBUSY; >>> + } >>> nested_vmx_vmexit(vcpu, EXIT_REASON_EXTERNAL_INTERRUPT, 0, 0); >>> } >>> >>> -- 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
