[PATCH v6 1/7] arm64: perf: Add missing ISB in armv8pmu_enable_event()

[Alexandru Elisei]

Writes to the PMXEVTYPER_EL0 register are not self-synchronising. In
armv8pmu_enable_event(), the PE can reorder configuring the event type
after we have enabled the counter and the interrupt. This can lead to an
interrupt being asserted because of the previous event type that we were
counting using the same counter, not the one that we've just configured.

The same rationale applies to writes to the PMINTENSET_EL1 register. The PE
can reorder enabling the interrupt at any point in the future after we have
enabled the event.

Prevent both situations from happening by adding an ISB just before we
enable the event counter.

Cc: Julien Thierry <julien.thierry.kdev at gmail.com>
Cc: Will Deacon <will.deacon at arm.com>
Cc: Mark Rutland <mark.rutland at arm.com>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Ingo Molnar <mingo at redhat.com>
Cc: Arnaldo Carvalho de Melo <acme at kernel.org>
Cc: Alexander Shishkin <alexander.shishkin at linux.intel.com>
Cc: Jiri Olsa <jolsa at redhat.com>
Cc: Namhyung Kim <namhyung at kernel.org>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Fixes: 030896885ade ("arm64: Performance counters support")
Reported-by: Julien Thierry <julien.thierry at arm.com>
Signed-off-by: Alexandru Elisei <alexandru.elisei at arm.com>
---
 arch/arm64/kernel/perf_event.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index 462f9a9cc44b..878e7087be02 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c
@@ -632,8 +632,10 @@ static void armv8pmu_enable_event(struct perf_event *event)
 	armv8pmu_enable_event_irq(event);
 
 	/*
-	 * Enable counter
+	 * Enable counter. Make sure event configuration register writes are
+	 * visible before we enable the counter.
 	 */
+	isb();
 	armv8pmu_enable_event_counter(event);
 
 	raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
-- 
2.28.0