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: a4eaf7f ("perf: Rework the PMU methods")
Reported-by: Dapeng Mi <[email protected]>
Reported-by: Ian Rogers <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Dapeng Mi <[email protected]>
Link: https://patch.msgid.link/[email protected]

Author: Peter Zijlstra

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