[PATCH 6.18 004/309] x86/perf: Make sure to program the counter value for stopped events on migration

Greg Kroah-Hartman
2026-03-31T16:57:36Z

From: Peter Zijlstra <peterz@infradead.org>

[ Upstream commit f1cac6ac62d28a9a57b17f51ac5795bf250c12d3 ]

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
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 6227690d19090..8a0cd2ebb60db 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -1361,8 +1361,10 @@ 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
--
2.51.0