Messages in this thread | | | Date | Wed, 6 Apr 2022 22:30:59 +0200 | From | "Maciej S. Szmigiero" <> | Subject | Re: [PATCH 5/8] KVM: SVM: Re-inject INT3/INTO instead of retrying the instruction |
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On 6.04.2022 21:48, Sean Christopherson wrote: > On Wed, Apr 06, 2022, Maciej S. Szmigiero wrote: >> On 6.04.2022 19:10, Sean Christopherson wrote: >>> On Wed, Apr 06, 2022, Maciej S. Szmigiero wrote: >> And what if it's L0 that is trying to inject a NMI into L2? >> In this case is_guest_mode() is true, but the full NMI injection machinery >> should be used. > > Gah, you're right, I got misled by a benign bug in nested_vmx_l1_wants_exit() and > was thinking that NMIs always exit. The "L1 wants" part should be conditioned on > NMI exiting being enabled. It's benign because KVM always wants "real" NMIs, and > so the path is never encountered. > > @@ -5980,7 +6005,7 @@ static bool nested_vmx_l1_wants_exit(struct kvm_vcpu *vcpu, > switch ((u16)exit_reason.basic) { > case EXIT_REASON_EXCEPTION_NMI: > intr_info = vmx_get_intr_info(vcpu); > - if (is_nmi(intr_info)) > + if (is_nmi(intr_info) && nested_cpu_has_nmi_exiting(vmcs12)) > return true; > else if (is_page_fault(intr_info)) > return true; >
I guess you mean "benign" when having KVM as L1, since other hypervisors may let their L2s handle NMIs themselves.
>> It is also incorrect to block L1 -> L2 NMI injection because either L1 >> or L2 is currently under NMI blocking: the first case is obvious, >> the second because it's L1 that is supposed to take care of proper NMI >> blocking for L2 when injecting an NMI there. > > Yep, but I don't think there's a bug here. At least not for nVMX.
I agree this scenario should currently work (including on nSVM) - mentioned it just as a constraint on solution space.
>>>> With the code in my previous patch set I planned to use >>>> exit_during_event_injection() to detect such case, but if we implement >>>> VMCB12 EVENTINJ parsing we can simply add a flag that the relevant event >>>> comes from L1, so its normal injection side-effects should be skipped. >>> >>> Do we still need a flag based on the above? Honest question... I've been staring >>> at all this for the better part of an hour and may have lost track of things. >> >> If checking just is_guest_mode() is not enough due to reasons I described >> above then we need to somehow determine in the NMI / IRQ injection handler >> whether the event to be injected into L2 comes from L0 or L1. >> For this (assuming we do VMCB12 EVENTINJ parsing) I think we need an extra flag. > > Yes :-( And I believe the extra flag would need to be handled by KVM_{G,S}ET_VCPU_EVENTS. >
Another option for saving and restoring a VM would be to add it to KVM_{GET,SET}_NESTED_STATE somewhere (maybe as a part of the saved VMCB12 control area?).
Thanks, Maciej
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