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Migrate the event >>>> + * to EXITINTINFO so that it's requeued instead of being dropped. >>>> + * >>>> + * An undelivered event doesn't imply a fatal VMEXIT_INVALID. With >>>> + * Enhanced SMT Protection, VMRUN may exit with an ordinary #VMEXIT >>>> + * without having injected that event into the guest. >>>> + * >>>> + * Clobbering EXITINTINFO is safe precisely because the vCPU never >>>> + * entered guest mode. >>>> + */ >>>> + if (control->event_inj) { >>> [Severity: High] >>> Does this code silently drop valid hardware-reported events? >>> >>> If an L1 hypervisor sets event_inj to a non-zero value but leaves the >>> SVM_EVTINJ_VALID bit clear, hardware will ignore the injection and won't >>> clear EVENTINJ. >> >> The first half is right, nested_svm_check_event_inj() intentionally returns >> true when V is clear, so vmcb02->control.event_inj can be non-zero with V=0. >> >> The second half isn't. Clearing EVENTINJ is not part of injection, it's part of >> #VMEXIT, and it's unconditional. > So that doesn't mesh with the above comment, which says: > > Hardware clears EVENTINJ field when it injects an event. > > And it begs the question of how this patch is at all useful. Because all this > fancy new paranoia is clearly generating #VMEXITs, and if #VMEXIT unconditionally > clears control->event_inj, I don't see how control->event_inj can be non-zero if > KVM attempted VMRUN. > > I.e. either this is all broken, or the APM is buggy. My wording in the comment is misleading. The clear is part of the #VMEXIT path out of guest mode, where it is indeed unconditional. However, VMRUN can terminate even before the guest mode is ever entered. With ESMTP, the hardware can give out a garden variety of exits at the sync point. In this case we get a VMEXIT that implies the VMRUN never actually ran any guest code then EVENTINJ won't be cleared. Since the exit code isn't a reliable discriminator, a non-zero EVENTINJ is the only way to tell. Thanks, --Pratik