linux-kernel - [PATCH v3 2/5] arm64: cpufeature: Add feature to detect heterogeneous systems

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Date:   Fri, 16 Aug 2019 13:59:31 +0100
From:   Raphael Gault <raphael.gault@....com>
To:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     mingo@...hat.com, peterz@...radead.org, catalin.marinas@....com,
        will.deacon@....com, acme@...nel.org, mark.rutland@....com,
        raph.gault+kdev@...il.com, Raphael Gault <raphael.gault@....com>
Subject: [PATCH v3 2/5] arm64: cpufeature: Add feature to detect heterogeneous systems

This feature is required in order to enable PMU counters direct
access from userspace only when the system is homogeneous.
This feature checks the model of each CPU brought online and compares it
to the boot CPU. If it differs then it is heterogeneous.

Signed-off-by: Raphael Gault <raphael.gault@....com>
---
 arch/arm64/include/asm/cpucaps.h |  3 ++-
 arch/arm64/kernel/cpufeature.c   | 20 ++++++++++++++++++++
 arch/arm64/kernel/perf_event.c   |  1 +
 3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
index f19fe4b9acc4..040370af38ad 100644
--- a/arch/arm64/include/asm/cpucaps.h
+++ b/arch/arm64/include/asm/cpucaps.h
@@ -52,7 +52,8 @@
 #define ARM64_HAS_IRQ_PRIO_MASKING		42
 #define ARM64_HAS_DCPODP			43
 #define ARM64_WORKAROUND_1463225		44
+#define ARM64_HAS_HETEROGENEOUS_PMU		45
 
-#define ARM64_NCAPS				45
+#define ARM64_NCAPS				46
 
 #endif /* __ASM_CPUCAPS_H */
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 9323bcc40a58..bbdd809f12a6 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1260,6 +1260,15 @@ static bool can_use_gic_priorities(const struct arm64_cpu_capabilities *entry,
 }
 #endif
 
+static bool has_heterogeneous_pmu(const struct arm64_cpu_capabilities *entry,
+				     int scope)
+{
+	u32 model = read_cpuid_id() & MIDR_CPU_MODEL_MASK;
+	struct cpuinfo_arm64 *boot = &per_cpu(cpu_data, 0);
+
+	return  (boot->reg_midr & MIDR_CPU_MODEL_MASK) != model;
+}
+
 static const struct arm64_cpu_capabilities arm64_features[] = {
 	{
 		.desc = "GIC system register CPU interface",
@@ -1560,6 +1569,16 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 		.min_field_value = 1,
 	},
 #endif
+	{
+		/*
+		 * Detect whether the system is heterogeneous or
+		 * homogeneous
+		 */
+		.desc = "Detect whether we have heterogeneous CPUs",
+		.capability = ARM64_HAS_HETEROGENEOUS_PMU,
+		.type = ARM64_CPUCAP_SCOPE_LOCAL_CPU | ARM64_CPUCAP_OPTIONAL_FOR_LATE_CPU,
+		.matches = has_heterogeneous_pmu,
+	},
 	{},
 };
 
@@ -1727,6 +1746,7 @@ static void __init setup_elf_hwcaps(const struct arm64_cpu_capabilities *hwcaps)
 			cap_set_elf_hwcap(hwcaps);
 }
 
+
 static void update_cpu_capabilities(u16 scope_mask)
 {
 	int i;
diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index 2d3bdebdf6df..a0b4f1bca491 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c
@@ -19,6 +19,7 @@
 #include <linux/of.h>
 #include <linux/perf/arm_pmu.h>
 #include <linux/platform_device.h>
+#include <linux/smp.h>
 
 /* ARMv8 Cortex-A53 specific event types. */
 #define ARMV8_A53_PERFCTR_PREF_LINEFILL				0xC2
-- 
2.17.1