diff options
Diffstat (limited to 'arch/x86/events/amd/ibs.c')
| -rw-r--r-- | arch/x86/events/amd/ibs.c | 52 |
1 files changed, 45 insertions, 7 deletions
diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c index 3ea25c3..feb90f6 100644 --- a/arch/x86/events/amd/ibs.c +++ b/arch/x86/events/amd/ibs.c @@ -28,10 +28,46 @@ static u32 ibs_caps; #define IBS_FETCH_CONFIG_MASK (IBS_FETCH_RAND_EN | IBS_FETCH_MAX_CNT) #define IBS_OP_CONFIG_MASK IBS_OP_MAX_CNT + +/* + * IBS states: + * + * ENABLED; tracks the pmu::add(), pmu::del() state, when set the counter is taken + * and any further add()s must fail. + * + * STARTED/STOPPING/STOPPED; deal with pmu::start(), pmu::stop() state but are + * complicated by the fact that the IBS hardware can send late NMIs (ie. after + * we've cleared the EN bit). + * + * In order to consume these late NMIs we have the STOPPED state, any NMI that + * happens after we've cleared the EN state will clear this bit and report the + * NMI handled (this is fundamentally racy in the face or multiple NMI sources, + * someone else can consume our BIT and our NMI will go unhandled). + * + * And since we cannot set/clear this separate bit together with the EN bit, + * there are races; if we cleared STARTED early, an NMI could land in + * between clearing STARTED and clearing the EN bit (in fact multiple NMIs + * could happen if the period is small enough), and consume our STOPPED bit + * and trigger streams of unhandled NMIs. + * + * If, however, we clear STARTED late, an NMI can hit between clearing the + * EN bit and clearing STARTED, still see STARTED set and process the event. + * If this event will have the VALID bit clear, we bail properly, but this + * is not a given. With VALID set we can end up calling pmu::stop() again + * (the throttle logic) and trigger the WARNs in there. + * + * So what we do is set STOPPING before clearing EN to avoid the pmu::stop() + * nesting, and clear STARTED late, so that we have a well defined state over + * the clearing of the EN bit. + * + * XXX: we could probably be using !atomic bitops for all this. + */ + enum ibs_states { IBS_ENABLED = 0, IBS_STARTED = 1, IBS_STOPPING = 2, + IBS_STOPPED = 3, IBS_MAX_STATES, }; @@ -377,11 +413,10 @@ static void perf_ibs_start(struct perf_event *event, int flags) perf_ibs_set_period(perf_ibs, hwc, &period); /* - * Set STARTED before enabling the hardware, such that - * a subsequent NMI must observe it. Then clear STOPPING - * such that we don't consume NMIs by accident. + * Set STARTED before enabling the hardware, such that a subsequent NMI + * must observe it. */ - set_bit(IBS_STARTED, pcpu->state); + set_bit(IBS_STARTED, pcpu->state); clear_bit(IBS_STOPPING, pcpu->state); perf_ibs_enable_event(perf_ibs, hwc, period >> 4); @@ -396,6 +431,9 @@ static void perf_ibs_stop(struct perf_event *event, int flags) u64 config; int stopping; + if (test_and_set_bit(IBS_STOPPING, pcpu->state)) + return; + stopping = test_bit(IBS_STARTED, pcpu->state); if (!stopping && (hwc->state & PERF_HES_UPTODATE)) @@ -405,12 +443,12 @@ static void perf_ibs_stop(struct perf_event *event, int flags) if (stopping) { /* - * Set STOPPING before disabling the hardware, such that it + * Set STOPPED before disabling the hardware, such that it * must be visible to NMIs the moment we clear the EN bit, * at which point we can generate an !VALID sample which * we need to consume. */ - set_bit(IBS_STOPPING, pcpu->state); + set_bit(IBS_STOPPED, pcpu->state); perf_ibs_disable_event(perf_ibs, hwc, config); /* * Clear STARTED after disabling the hardware; if it were @@ -556,7 +594,7 @@ fail: * with samples that even have the valid bit cleared. * Mark all this NMIs as handled. */ - if (test_and_clear_bit(IBS_STOPPING, pcpu->state)) + if (test_and_clear_bit(IBS_STOPPED, pcpu->state)) return 1; return 0; |
