[PATCH] powerpc/perf: Fix PMU callbacks to clear pending PMI before resetting an overflown PMC
Athira Rajeev
atrajeev at linux.vnet.ibm.com
Wed Apr 7 00:40:10 AEST 2021
Hi,
Cover letter is missing in this patch. I will resent the patch along with cover letter.
Sorry for the noise.
Thanks,
Athira
> On 06-Apr-2021, at 7:44 PM, Athira Rajeev <atrajeev at linux.vnet.ibm.com> wrote:
>
> Running perf fuzzer showed below in dmesg logs:
> "Can't find PMC that caused IRQ"
>
> This means a PMU exception happened, but none of the PMC's (Performance
> Monitor Counter) were found to be overflown. There are some corner cases
> that clears the PMCs after PMI gets masked. In such cases, the perf
> interrupt handler will not find the active PMC values that had caused
> the overflow and thus leads to this message while replaying.
>
> Case 1: PMU Interrupt happens during replay of other interrupts and
> counter values gets cleared by PMU callbacks before replay:
>
> During replay of interrupts like timer, __do_irq and doorbell exception, we
> conditionally enable interrupts via may_hard_irq_enable(). This could
> potentially create a window to generate a PMI. Since irq soft mask is set
> to ALL_DISABLED, the PMI will get masked here. We could get IPIs run before
> perf interrupt is replayed and the PMU events could deleted or stopped.
> This will change the PMU SPR values and resets the counters. Snippet of
> ftrace log showing PMU callbacks invoked in "__do_irq":
>
> <idle>-0 [051] dns. 132025441306354: __do_irq <-call_do_irq
> <idle>-0 [051] dns. 132025441306430: irq_enter <-__do_irq
> <idle>-0 [051] dns. 132025441306503: irq_enter_rcu <-__do_irq
> <idle>-0 [051] dnH. 132025441306599: xive_get_irq <-__do_irq
> <<>>
> <idle>-0 [051] dnH. 132025441307770: generic_smp_call_function_single_interrupt <-smp_ipi_demux_relaxed
> <idle>-0 [051] dnH. 132025441307839: flush_smp_call_function_queue <-smp_ipi_demux_relaxed
> <idle>-0 [051] dnH. 132025441308057: _raw_spin_lock <-event_function
> <idle>-0 [051] dnH. 132025441308206: power_pmu_disable <-perf_pmu_disable
> <idle>-0 [051] dnH. 132025441308337: power_pmu_del <-event_sched_out
> <idle>-0 [051] dnH. 132025441308407: power_pmu_read <-power_pmu_del
> <idle>-0 [051] dnH. 132025441308477: read_pmc <-power_pmu_read
> <idle>-0 [051] dnH. 132025441308590: isa207_disable_pmc <-power_pmu_del
> <idle>-0 [051] dnH. 132025441308663: write_pmc <-power_pmu_del
> <idle>-0 [051] dnH. 132025441308787: power_pmu_event_idx <-perf_event_update_userpage
> <idle>-0 [051] dnH. 132025441308859: rcu_read_unlock_strict <-perf_event_update_userpage
> <idle>-0 [051] dnH. 132025441308975: power_pmu_enable <-perf_pmu_enable
> <<>>
> <idle>-0 [051] dnH. 132025441311108: irq_exit <-__do_irq
> <idle>-0 [051] dns. 132025441311319: performance_monitor_exception <-replay_soft_interrupts
>
> Case 2: PMI's masked during local_* operations, example local_add.
> If the local_add operation happens within a local_irq_save, replay of
> PMI will be during local_irq_restore. Similar to case 1, this could
> also create a window before replay where PMU events gets deleted or
> stopped.
>
> Patch adds a fix to update the PMU callback functions (del,stop,enable) to
> check for pending perf interrupt. If there is an overflown PMC and pending
> perf interrupt indicated in Paca, clear the PMI bit in paca to drop that
> sample. In case of power_pmu_del, also clear the MMCR0 PMAO bit which
> otherwise could lead to spurious interrupts in some corner cases. Example,
> a timer after power_pmu_del which will re-enable interrupts since PMI is
> cleared and triggers a PMI again since PMAO bit is still set.
>
> We can't just replay PMI any time. Hence this approach is preferred rather
> than replaying PMI before resetting overflown PMC. Patch also documents
> core-book3s on a race condition which can trigger these PMC messages during
> idle path in PowerNV.
>
> Fixes: f442d004806e ("powerpc/64s: Add support to mask perf interrupts and replay them")
> Reported-by: Nageswara R Sastry <nasastry at in.ibm.com>
> Suggested-by: Nicholas Piggin <npiggin at gmail.com>
> Suggested-by: Madhavan Srinivasan <maddy at linux.ibm.com>
> Signed-off-by: Athira Rajeev <atrajeev at linux.vnet.ibm.com>
> ---
> arch/powerpc/include/asm/pmc.h | 11 +++++++++
> arch/powerpc/perf/core-book3s.c | 55 +++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 66 insertions(+)
>
> diff --git a/arch/powerpc/include/asm/pmc.h b/arch/powerpc/include/asm/pmc.h
> index c6bbe9778d3c..97b4bd8de25b 100644
> --- a/arch/powerpc/include/asm/pmc.h
> +++ b/arch/powerpc/include/asm/pmc.h
> @@ -34,11 +34,22 @@ static inline void ppc_set_pmu_inuse(int inuse)
> #endif
> }
>
> +static inline int clear_paca_irq_pmi(void)
> +{
> + if (get_paca()->irq_happened & PACA_IRQ_PMI) {
> + WARN_ON_ONCE(mfmsr() & MSR_EE);
> + get_paca()->irq_happened &= ~PACA_IRQ_PMI;
> + return 1;
> + }
> + return 0;
> +}
> +
> extern void power4_enable_pmcs(void);
>
> #else /* CONFIG_PPC64 */
>
> static inline void ppc_set_pmu_inuse(int inuse) { }
> +static inline int clear_paca_irq_pmi(void) { return 0; }
>
> #endif
>
> diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
> index 766f064f00fb..18ca3c90f866 100644
> --- a/arch/powerpc/perf/core-book3s.c
> +++ b/arch/powerpc/perf/core-book3s.c
> @@ -847,6 +847,20 @@ static void write_pmc(int idx, unsigned long val)
> }
> }
>
> +static int pmc_overflown(int idx)
> +{
> + unsigned long val[8];
> + int i;
> +
> + for (i = 0; i < ppmu->n_counter; i++)
> + val[i] = read_pmc(i + 1);
> +
> + if ((int)val[idx-1] < 0)
> + return 1;
> +
> + return 0;
> +}
> +
> /* Called from sysrq_handle_showregs() */
> void perf_event_print_debug(void)
> {
> @@ -1438,6 +1452,15 @@ static void power_pmu_enable(struct pmu *pmu)
> event = cpuhw->event[i];
> if (event->hw.idx && event->hw.idx != hwc_index[i] + 1) {
> power_pmu_read(event);
> + /*
> + * if the PMC corresponding to event->hw.idx is
> + * overflown, check if there is any pending perf
> + * interrupt set in paca. If so, disable the interrupt
> + * by clearing the paca bit for PMI since we are going
> + * to reset the PMC.
> + */
> + if (pmc_overflown(event->hw.idx))
> + clear_paca_irq_pmi();
> write_pmc(event->hw.idx, 0);
> event->hw.idx = 0;
> }
> @@ -1474,6 +1497,10 @@ static void power_pmu_enable(struct pmu *pmu)
> event->hw.idx = idx;
> if (event->hw.state & PERF_HES_STOPPED)
> val = 0;
> +
> + /* See above for clear_paca_irq_pmi */
> + if (pmc_overflown(event->hw.idx))
> + clear_paca_irq_pmi();
> write_pmc(idx, val);
>
> perf_event_update_userpage(event);
> @@ -1619,6 +1646,7 @@ static void power_pmu_del(struct perf_event *event, int ef_flags)
> struct cpu_hw_events *cpuhw;
> long i;
> unsigned long flags;
> + unsigned long val_mmcr0;
>
> local_irq_save(flags);
> perf_pmu_disable(event->pmu);
> @@ -1636,6 +1664,22 @@ static void power_pmu_del(struct perf_event *event, int ef_flags)
> --cpuhw->n_events;
> ppmu->disable_pmc(event->hw.idx - 1, &cpuhw->mmcr);
> if (event->hw.idx) {
> + /*
> + * if the PMC corresponding to event->hw.idx is
> + * overflown, check if there is any pending perf
> + * interrupt set in paca. If so, disable the interrupt
> + * and clear the MMCR0 PMAO bit since we are going
> + * to reset the PMC and delete the event.
> + */
> + if (pmc_overflown(event->hw.idx)) {
> + if (clear_paca_irq_pmi()) {
> + val_mmcr0 = mfspr(SPRN_MMCR0);
> + val_mmcr0 &= ~MMCR0_PMAO;
> + write_mmcr0(cpuhw, val_mmcr0);
> + mb();
> + isync();
> + }
> + }
> write_pmc(event->hw.idx, 0);
> event->hw.idx = 0;
> }
> @@ -1714,6 +1758,8 @@ static void power_pmu_stop(struct perf_event *event, int ef_flags)
>
> local_irq_save(flags);
> perf_pmu_disable(event->pmu);
> + if (pmc_overflown(event->hw.idx))
> + clear_paca_irq_pmi();
>
> power_pmu_read(event);
> event->hw.state |= PERF_HES_STOPPED | PERF_HES_UPTODATE;
> @@ -2343,6 +2389,15 @@ static void __perf_event_interrupt(struct pt_regs *regs)
> }
> }
> }
> +
> + /*
> + * During system wide profling or while specific CPU
> + * is monitored for an event, some corner cases could
> + * cause PMC to overflow in idle path. This will trigger
> + * a PMI after waking up from idle. Since counter values
> + * are _not_ saved/restored in idle path, can lead to
> + * below "Can't find PMC" message.
> + */
> if (unlikely(!found) && !arch_irq_disabled_regs(regs))
> printk_ratelimited(KERN_WARNING "Can't find PMC that caused IRQ\n");
>
> --
> 1.8.3.1
>
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