linux-kernel - [PATCH AUTOSEL 5.15 04/12] drivers/perf: pmuv3: don't expose SW

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Message-ID: <20240115232718.209642-4-sashal@kernel.org>
Date: Mon, 15 Jan 2024 18:26:49 -0500
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Mark Rutland <mark.rutland@....com>,
	Will Deacon <will@...nel.org>,
	Sasha Levin <sashal@...nel.org>,
	peterz@...radead.org,
	mingo@...hat.com,
	acme@...nel.org,
	catalin.marinas@....com,
	linux-arm-kernel@...ts.infradead.org,
	linux-perf-users@...r.kernel.org
Subject: [PATCH AUTOSEL 5.15 04/12] drivers/perf: pmuv3: don't expose SW_INCR event in sysfs

From: Mark Rutland <mark.rutland@....com>

[ Upstream commit ca6f537e459e2da4b331fe8928d1a0b0f9301f42 ]

The SW_INCR event is somewhat unusual, and depends on the specific HW
counter that it is programmed into. When programmed into PMEVCNTR<n>,
SW_INCR will count any writes to PMSWINC_EL0 with bit n set, ignoring
writes to SW_INCR with bit n clear.

Event rotation means that there's no fixed relationship between
perf_events and HW counters, so this isn't all that useful.

Further, we program PMUSERENR.{SW,EN}=={0,0}, which causes EL0 writes to
PMSWINC_EL0 to be trapped and handled as UNDEFINED, resulting in a
SIGILL to userspace.

Given that, it's not a good idea to expose SW_INCR in sysfs. Hide it as
we did for CHAIN back in commit:

  4ba2578fa7b55701 ("arm64: perf: don't expose CHAIN event in sysfs")

Signed-off-by: Mark Rutland <mark.rutland@....com>
Cc: Will Deacon <will@...nel.org>
Link: https://lore.kernel.org/r/20231204115847.2993026-1-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/arm64/kernel/perf_event.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index b4044469527e..c77b9460d63e 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c
@@ -168,7 +168,11 @@ armv8pmu_events_sysfs_show(struct device *dev,
 	PMU_EVENT_ATTR_ID(name, armv8pmu_events_sysfs_show, config)
 
 static struct attribute *armv8_pmuv3_event_attrs[] = {
-	ARMV8_EVENT_ATTR(sw_incr, ARMV8_PMUV3_PERFCTR_SW_INCR),
+	/*
+	 * Don't expose the sw_incr event in /sys. It's not usable as writes to
+	 * PMSWINC_EL0 will trap as PMUSERENR.{SW,EN}=={0,0} and event rotation
+	 * means we don't have a fixed event<->counter relationship regardless.
+	 */
 	ARMV8_EVENT_ATTR(l1i_cache_refill, ARMV8_PMUV3_PERFCTR_L1I_CACHE_REFILL),
 	ARMV8_EVENT_ATTR(l1i_tlb_refill, ARMV8_PMUV3_PERFCTR_L1I_TLB_REFILL),
 	ARMV8_EVENT_ATTR(l1d_cache_refill, ARMV8_PMUV3_PERFCTR_L1D_CACHE_REFILL),
-- 
2.43.0