linux-kernel - [PATCH V2 3/5] perf/x86/intel: Filter unsupported Topdown metrics event

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Date:   Wed, 27 Jan 2021 07:38:43 -0800
From:   kan.liang@...ux.intel.com
To:     peterz@...radead.org, acme@...nel.org, mingo@...nel.org,
        linux-kernel@...r.kernel.org
Cc:     eranian@...gle.com, namhyung@...nel.org, jolsa@...hat.com,
        ak@...ux.intel.com, yao.jin@...ux.intel.com, mpe@...erman.id.au,
        maddy@...ux.vnet.ibm.com, Kan Liang <kan.liang@...ux.intel.com>
Subject: [PATCH V2 3/5] perf/x86/intel: Filter unsupported Topdown metrics event

From: Kan Liang <kan.liang@...ux.intel.com>

Current perf doesn't check the index of a Topdown metrics event before
updating the event. A perf tool user may get a value from an unsupported
Topdown metrics event.

For example, the L2 topdown event, cpu/event=0x00,umask=0x84/, is not
supported on Ice Lake. A perf tool user may mistakenly use the
unsupported events via RAW format. In this case, the scheduler follows
the unknown event handling and assigns a GP counter to the event. The
icl_get_topdown_value() returns the value of the slots to the event.
The perf tool user will get the value for the unsupported
Topdown metrics event.

Add a check in the __icl_update_topdown_event() and avoid updating
unsupported events.

Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
---
 arch/x86/events/intel/core.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 8eba41b..b02d482 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -2319,6 +2319,17 @@ static void __icl_update_topdown_event(struct perf_event *event,
 {
 	u64 delta, last = 0;

+	/*
+	 * Although the unsupported topdown events are not exposed to users,
+	 * users may mistakenly use the unsupported events via RAW format.
+	 * For example, using L2 topdown event, cpu/event=0x00,umask=0x84/,
+	 * on Ice Lake. In this case, the scheduler follows the unknown
+	 * event handling and assigns a GP counter to the event.
+	 * Check the case, and avoid updating unsupported events.
+	 */
+	if (event->hw.idx < INTEL_PMC_IDX_FIXED)
+		return;
+
 	delta = icl_get_topdown_value(event, slots, metrics);
 	if (last_slots)
 		last = icl_get_topdown_value(event, last_slots, last_metrics);
-- 
2.7.4