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Peter Anvin" CC: , , Xin Li , Andy Lutomirski , Thomas Gleixner , "Ingo Molnar" , Borislav Petkov , Dave Hansen , Sean Christopherson , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , "Alexander Shishkin" , Jiri Olsa , Ian Rogers , Adrian Hunter , "Kan Liang" , Tony Luck , "Paolo Bonzini" , Vitaly Kuznetsov , "Rafael J . Wysocki" , Daniel Lezcano , Zhang Rui , Lukasz Luba , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Brian Gerst , Andrew Cooper , "Kirill A . 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Peter Anvin wrote: >> On May 8, 2025 5:15:44 AM PDT, Peter Zijlstra wrote: > >>>> Looks good, except when fred_event_data() returns 0. I don't expect it >>>> to happen in practice. But, maybe with new hardware and eventually >>>> different hypervisors being involved, it is a possibility. >>>> >>>> We can either call it a bug that an NMI happened without source >>>> information. Or be extra nice and do this: >>>> >>>> if (cpu_feature_enabled(X86_FEATURE_NMI_SOURCE) && type == NMI_LOCAL) { >>>> source = fred_event_data(regs); >>>> if (!source || (source & BIT(0))) >>>> source = ~0UL; >>>> } >>> >>> Perhaps also WARN about the !source case? >> >> A 0 should be interpreted such that NMI source is not available, e.g. >> due to a broken hypervisor or similar. > > I'm reading that as an agreement for WARN-ing on 0. We should definitely > WARN on broken hypervisors and similar. Yup, will do.