From f1cac6ac62d28a9a57b17f51ac5795bf250c12d3 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 11 Mar 2026 21:29:14 +0100 Subject: [PATCH] x86/perf: Make sure to program the counter value for stopped events on migration Both Mi Dapeng and Ian Rogers noted that not everything that sets HES_STOPPED is required to EF_UPDATE. Specifically the 'step 1' loop of rescheduling explicitly does EF_UPDATE to ensure the counter value is read. However, then 'step 2' simply leaves the new counter uninitialized when HES_STOPPED, even though, as noted above, the thing that stopped them might not be aware it needs to EF_RELOAD -- since it didn't EF_UPDATE on stop. One such location that is affected is throttling, throttle does pmu->stop(, 0); and unthrottle does pmu->start(, 0); possibly restarting an uninitialized counter. Fixes: a4eaf7f14675 ("perf: Rework the PMU methods") Reported-by: Dapeng Mi Reported-by: Ian Rogers Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Dapeng Mi Link: https://patch.msgid.link/20260311204035.GX606826@noisy.programming.kicks-ass.net --- arch/x86/events/core.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index 54b4c315d927..810ab21ffd99 100644 --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -1374,8 +1374,10 @@ static void x86_pmu_enable(struct pmu *pmu) cpuc->events[hwc->idx] = event; - if (hwc->state & PERF_HES_ARCH) + if (hwc->state & PERF_HES_ARCH) { + static_call(x86_pmu_set_period)(event); continue; + } /* * if cpuc->enabled = 0, then no wrmsr as