linux-kernel - [PATCH 3/5] arm64: perf: Only advertise cap_user_time for arch

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Date:   Tue, 12 May 2020 14:41:01 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Leo Yan <leo.yan@...aro.org>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        mingo@...hat.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        daniel.lezcano@...aro.org, tglx@...utronix.de,
        sboyd@...eaurora.org, john.stultz@...aro.org,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: [PATCH 3/5] arm64: perf: Only advertise cap_user_time for arch_timer

When sched_clock is running on anything other than arch_timer, don't
advertise cap_user_time*.

Requested-by: Will Deacon <will@...nel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/arm64/kernel/perf_event.c |   19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c
@@ -13,6 +13,8 @@
 #include <asm/sysreg.h>
 #include <asm/virt.h>
 
+#include <clocksource/arm_arch_timer.h>
+
 #include <linux/acpi.h>
 #include <linux/clocksource.h>
 #include <linux/kvm_host.h>
@@ -1169,16 +1171,15 @@ void arch_perf_update_userpage(struct pe
 	struct clock_read_data *rd;
 	unsigned int seq;
 
-	/*
-	 * Internal timekeeping for enabled/running/stopped times
-	 * is always computed with the sched_clock.
-	 */
-	userpg->cap_user_time = 1;
-	userpg->cap_user_time_zero = 1;
+	userpg->cap_user_time = 0;
+	userpg->cap_user_time_zero = 0;
 
 	do {
 		rd = sched_clock_read_begin(&seq);
 
+		if (rd->read_sched_clock != arch_timer_read_counter)
+			return;
+
 		userpg->time_mult = rd->mult;
 		userpg->time_shift = rd->shift;
 		userpg->time_zero = rd->epoch_ns;
@@ -1207,4 +1208,10 @@ void arch_perf_update_userpage(struct pe
 		userpg->time_mult >>= 1;
 	}
 
+	/*
+	 * Internal timekeeping for enabled/running/stopped times
+	 * is always computed with the sched_clock.
+	 */
+	userpg->cap_user_time = 1;
+	userpg->cap_user_time_zero = 1;
 }