linux-kernel - [RFCv1 4/4] perf: arm_spe: Dynamically switch PID tracing to contextidr

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Date:   Thu, 21 Oct 2021 21:45:30 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Kees Cook <keescook@...omium.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Nicholas Piggin <npiggin@...il.com>,
        James Morse <james.morse@....com>,
        Marc Zyngier <maz@...nel.org>, Joey Gouly <joey.gouly@....com>,
        Peter Collingbourne <pcc@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Stephane Eranian <eranian@...gle.com>,
        James Clark <james.clark@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Leo Yan <leo.yan@...aro.org>
Subject: [RFCv1 4/4] perf: arm_spe: Dynamically switch PID tracing to contextidr

Now Arm64 provides API for enabling and disable PID tracing, Arm SPE
driver invokes these functions to dynamically enable it during
profiling when the program runs in root PID name space, and disable PID
tracing when the perf event is stopped.

Device drivers should not depend on CONFIG_PID_IN_CONTEXTIDR for PID
tracing, so this patch uses the consistent condition for setting bit
EL1_CX for PMSCR.

Signed-off-by: Leo Yan <leo.yan@...aro.org>
---
 drivers/perf/arm_spe_pmu.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/perf/arm_spe_pmu.c b/drivers/perf/arm_spe_pmu.c
index d44bcc29d99c..935343cdcb39 100644
--- a/drivers/perf/arm_spe_pmu.c
+++ b/drivers/perf/arm_spe_pmu.c
@@ -23,6 +23,7 @@
 #include <linux/irq.h>
 #include <linux/kernel.h>
 #include <linux/list.h>
+#include <linux/mmu_context.h>
 #include <linux/module.h>
 #include <linux/of_address.h>
 #include <linux/of_device.h>
@@ -272,7 +273,7 @@ static u64 arm_spe_event_to_pmscr(struct perf_event *event)
 	if (!attr->exclude_kernel)
 		reg |= BIT(SYS_PMSCR_EL1_E1SPE_SHIFT);
 
-	if (IS_ENABLED(CONFIG_PID_IN_CONTEXTIDR) && perfmon_capable())
+	if (perfmon_capable() && (task_active_pid_ns(current) == &init_pid_ns))
 		reg |= BIT(SYS_PMSCR_EL1_CX_SHIFT);
 
 	return reg;
@@ -731,6 +732,13 @@ static void arm_spe_pmu_start(struct perf_event *event, int flags)
 	if (hwc->state)
 		return;
 
+	/*
+	 * Enable tracing PID to contextidr if profiling program runs in
+	 * root PID namespace.
+	 */
+	if (perfmon_capable() && (task_active_pid_ns(current) == &init_pid_ns))
+		contextidr_enable();
+
 	reg = arm_spe_event_to_pmsfcr(event);
 	write_sysreg_s(reg, SYS_PMSFCR_EL1);
 
@@ -792,6 +800,9 @@ static void arm_spe_pmu_stop(struct perf_event *event, int flags)
 	}
 
 	hwc->state |= PERF_HES_STOPPED;
+
+	if (perfmon_capable() && (task_active_pid_ns(current) == &init_pid_ns))
+		contextidr_disable();
 }
 
 static int arm_spe_pmu_add(struct perf_event *event, int flags)
-- 
2.25.1