Messages in this thread | | | Subject | Re: [RFC][PATCH 4/6] x86, nmi: add in logic to handle multiple events and unknown NMIs | From | Peter Zijlstra <> | Date | Mon, 22 Aug 2011 16:22:15 +0200 |
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On Fri, 2011-08-19 at 16:37 -0400, Don Zickus wrote: > @@ -260,6 +260,8 @@ unknown_nmi_error(unsigned char reason, struct pt_regs *regs) > pr_emerg("Dazed and confused, but trying to continue\n"); > } > > +DEFINE_PER_CPU(bool, swallow_nmi); > + > static notrace __kprobes void default_do_nmi(struct pt_regs *regs) > { > unsigned char reason = 0; > @@ -271,8 +273,28 @@ static notrace __kprobes void default_do_nmi(struct pt_regs *regs) > * NMI can not be detected/processed on other CPUs. > */ > handled = nmi_handle(NMI_LOCAL, regs); > - if (handled) > + if (handled) { > + /* > + * When handling multiple NMI events, we are not > + * sure if the second NMI was dropped (because of > + * too many NMIs), piggy-backed on the same NMI > + * (perf) or is queued right behind this NMI. > + * In the last case, we may accidentally get an > + * unknown NMI because the event is already handled. > + * Flag for this condition and swallow it later. > + * > + * FIXME: This detection has holes in it mainly > + * because we can't tell _when_ the next NMI comes > + * in. A multi-handled NMI event followed by an > + * unknown NMI a second later, clearly should not > + * be swallowed. > + */ > + if (handled > 1) > + __this_cpu_write(swallow_nmi, true); > + else > + __this_cpu_write(swallow_nmi, false); > return; > + } > > /* Non-CPU-specific NMI: NMI sources can be processed on any CPU */ > raw_spin_lock(&nmi_reason_lock); > @@ -296,6 +318,8 @@ static notrace __kprobes void default_do_nmi(struct pt_regs *regs) > raw_spin_unlock(&nmi_reason_lock); > > unknown_nmi_error(reason, regs); > + > + __this_cpu_write(swallow_nmi, false); > }
All writes, no reads... the actual dropping of NMIs got lost and now lives in patch 5 which purports to be about statistics only.
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