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 <dapeng1.mi@linux.intel.com>
Reported-by: Ian Rogers <irogers@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Link: https://patch.msgid.link/20260311204035.GX606826@noisy.programming.kicks-ass.net

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 54b4c315d927f82e06c27bb3e8ff16ff916fbd17..810ab21ffd991322600ece5c299bd5287a0286bc 100644 (file)
--- 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