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Subject[PATCH v3 1/7] arm64: add support for the AMU extension v1
Date
The activity monitors extension is an optional extension introduced
by the ARMv8.4 CPU architecture. This implements basic support for
version 1 of the activity monitors architecture, AMUv1.

This support includes:
- Extension detection on each CPU (boot, secondary, hotplugged)
- Register interface for AMU aarch64 registers
- disable_amu kernel parameter to disable detection/counter access
at runtime

Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
---
.../admin-guide/kernel-parameters.txt | 10 ++
arch/arm64/Kconfig | 31 ++++++
arch/arm64/include/asm/cpucaps.h | 3 +-
arch/arm64/include/asm/cpufeature.h | 5 +
arch/arm64/include/asm/sysreg.h | 38 ++++++++
arch/arm64/kernel/cpufeature.c | 97 +++++++++++++++++++
6 files changed, 183 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index ade4e6ec23e0..6f0c6d22fa4c 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -843,6 +843,16 @@
can be useful when debugging issues that require an SLB
miss to occur.

+ disable_amu [ARM64]
+ Disables detection, enablement and access to counter
+ registers of the Activity Monitors Unit (AMU). By
+ default these are enabled. "disable_amu=0/1" is also
+ allowed.
+ disable_amu / disable_amu=1 - ensures access to AMU's
+ counter registers is not attempted.
+ disable_amu=0 - enables or maintain detection and
+ access to AMU's counter registers.
+
disable= [IPV6]
See Documentation/networking/ipv6.txt.

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 3ab05857ca8f..b3408d7629fd 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1484,6 +1484,37 @@ config ARM64_PTR_AUTH

endmenu

+menu "ARMv8.4 architectural features"
+
+config ARM64_AMU_EXTN
+ bool "Enable support for the Activity Monitors Unit CPU extension"
+ default y
+ help
+ The activity monitors extension is an optional extension introduced
+ by the ARMv8.4 CPU architecture. This enables support for version 1
+ of the activity monitors architecture, AMUv1.
+
+ To enable the use of this extension on CPUs that implement it, say Y.
+
+ Note that for architectural reasons, firmware _must_ implement AMU
+ support when running on CPUs that present the activity monitors
+ extension. The required support is present in:
+ * Version 1.5 and later of the ARM Trusted Firmware
+
+ For kernels that have this configuration enabled but boot with broken
+ firmware, you may need to say N here until the firmware is fixed.
+ Otherwise you may experience firmware panics or lockups when
+ accessing the counter registers. Even if you are not observing these
+ symptoms, the values returned by the register reads might not
+ correctly reflect reality. Most commonly, the value read will be 0,
+ indicating that the counter is not enabled.
+
+ Alternatively, a kernel parameter is provided to disable detection,
+ enablement and access to the counter registers of the Activity
+ Monitors Unit at runtime.
+
+endmenu
+
config ARM64_SVE
bool "ARM Scalable Vector Extension support"
default y
diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
index b92683871119..7dde890bde50 100644
--- a/arch/arm64/include/asm/cpucaps.h
+++ b/arch/arm64/include/asm/cpucaps.h
@@ -56,7 +56,8 @@
#define ARM64_WORKAROUND_CAVIUM_TX2_219_PRFM 46
#define ARM64_WORKAROUND_1542419 47
#define ARM64_WORKAROUND_1319367 48
+#define ARM64_HAS_AMU_EXTN 49

-#define ARM64_NCAPS 49
+#define ARM64_NCAPS 50

#endif /* __ASM_CPUCAPS_H */
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 4261d55e8506..5ae6e00ccabb 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -673,6 +673,11 @@ static inline bool cpu_has_hw_af(void)
ID_AA64MMFR1_HADBS_SHIFT);
}

+#ifdef CONFIG_ARM64_AMU_EXTN
+/* Check whether the current CPU supports the Activity Monitors Unit (AMU) */
+extern bool cpu_has_amu_feat(int cpu);
+#endif
+
#endif /* __ASSEMBLY__ */

#endif
diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index 6e919fafb43d..eba13b8994ce 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -382,6 +382,42 @@
#define SYS_TPIDR_EL0 sys_reg(3, 3, 13, 0, 2)
#define SYS_TPIDRRO_EL0 sys_reg(3, 3, 13, 0, 3)

+/* Definitions for system register interface to AMU for ARMv8.4 onwards */
+#define SYS_AM_EL0(crm, op2) sys_reg(3, 3, 13, (crm), (op2))
+#define SYS_AMCR_EL0 SYS_AM_EL0(2, 0)
+#define SYS_AMCFGR_EL0 SYS_AM_EL0(2, 1)
+#define SYS_AMCGCR_EL0 SYS_AM_EL0(2, 2)
+#define SYS_AMUSERENR_EL0 SYS_AM_EL0(2, 3)
+#define SYS_AMCNTENCLR0_EL0 SYS_AM_EL0(2, 4)
+#define SYS_AMCNTENSET0_EL0 SYS_AM_EL0(2, 5)
+#define SYS_AMCNTENCLR1_EL0 SYS_AM_EL0(3, 0)
+#define SYS_AMCNTENSET1_EL0 SYS_AM_EL0(3, 1)
+
+/*
+ * Group 0 of activity monitors (architected):
+ * op0 op1 CRn CRm op2
+ * Counter: 11 011 1101 010:n<3> n<2:0>
+ * Type: 11 011 1101 011:n<3> n<2:0>
+ * n: 0-15
+ *
+ * Group 1 of activity monitors (auxiliary):
+ * op0 op1 CRn CRm op2
+ * Counter: 11 011 1101 110:n<3> n<2:0>
+ * Type: 11 011 1101 111:n<3> n<2:0>
+ * n: 0-15
+ */
+
+#define SYS_AMEVCNTR0_EL0(n) SYS_AM_EL0(4 + ((n) >> 3), (n) & 7)
+#define SYS_AMEVTYPE0_EL0(n) SYS_AM_EL0(6 + ((n) >> 3), (n) & 7)
+#define SYS_AMEVCNTR1_EL0(n) SYS_AM_EL0(12 + ((n) >> 3), (n) & 7)
+#define SYS_AMEVTYPE1_EL0(n) SYS_AM_EL0(14 + ((n) >> 3), (n) & 7)
+
+/* AMU v1: Fixed (architecturally defined) activity monitors */
+#define SYS_AMEVCNTR0_CORE_EL0 SYS_AMEVCNTR0_EL0(0)
+#define SYS_AMEVCNTR0_CONST_EL0 SYS_AMEVCNTR0_EL0(1)
+#define SYS_AMEVCNTR0_INST_RET_EL0 SYS_AMEVCNTR0_EL0(2)
+#define SYS_AMEVCNTR0_MEM_STALL SYS_AMEVCNTR0_EL0(3)
+
#define SYS_CNTFRQ_EL0 sys_reg(3, 3, 14, 0, 0)

#define SYS_CNTP_TVAL_EL0 sys_reg(3, 3, 14, 2, 0)
@@ -577,6 +613,7 @@
#define ID_AA64PFR0_CSV3_SHIFT 60
#define ID_AA64PFR0_CSV2_SHIFT 56
#define ID_AA64PFR0_DIT_SHIFT 48
+#define ID_AA64PFR0_AMU_SHIFT 44
#define ID_AA64PFR0_SVE_SHIFT 32
#define ID_AA64PFR0_RAS_SHIFT 28
#define ID_AA64PFR0_GIC_SHIFT 24
@@ -587,6 +624,7 @@
#define ID_AA64PFR0_EL1_SHIFT 4
#define ID_AA64PFR0_EL0_SHIFT 0

+#define ID_AA64PFR0_AMU 0x1
#define ID_AA64PFR0_SVE 0x1
#define ID_AA64PFR0_RAS_V1 0x1
#define ID_AA64PFR0_FP_NI 0xf
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 04cf64e9f0c9..029a473ad273 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -156,6 +156,7 @@ static const struct arm64_ftr_bits ftr_id_aa64pfr0[] = {
ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_CSV3_SHIFT, 4, 0),
ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_CSV2_SHIFT, 4, 0),
ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_DIT_SHIFT, 4, 0),
+ ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_AMU_SHIFT, 4, 0),
ARM64_FTR_BITS(FTR_VISIBLE_IF_IS_ENABLED(CONFIG_ARM64_SVE),
FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_SVE_SHIFT, 4, 0),
ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_RAS_SHIFT, 4, 0),
@@ -1150,6 +1151,84 @@ static bool has_hw_dbm(const struct arm64_cpu_capabilities *cap,

#endif

+#ifdef CONFIG_ARM64_AMU_EXTN
+
+/*
+ * The "amu_cpus" cpumask only signals that the CPU implementation for the
+ * flagged CPUs supports the Activity Monitors Unit (AMU) but does not provide
+ * information regarding all the events that it supports. When a CPU bit is
+ * set in the cpumask, the user of this feature can only rely on the presence
+ * of the 4 fixed counters for that CPU. But this does not guarantee that the
+ * counters are enabled or access to these counters is enabled by code
+ * executed at higher exception levels (firmware).
+ */
+static cpumask_var_t amu_cpus;
+
+bool cpu_has_amu_feat(int cpu)
+{
+ if (cpumask_available(amu_cpus))
+ return cpumask_test_cpu(cpu, amu_cpus);
+
+ return false;
+}
+
+static void cpu_amu_enable(struct arm64_cpu_capabilities const *cap)
+{
+ if (has_cpuid_feature(cap, SCOPE_LOCAL_CPU)) {
+ pr_info("detected CPU%d: Activity Monitors Unit (AMU)\n",
+ smp_processor_id());
+ cpumask_set_cpu(smp_processor_id(), amu_cpus);
+ }
+}
+
+/*
+ * For known broken firmware, a kernel parameter ("disable_amu") is provided
+ * to ensure access to AMU counter registers is not attempted. By default,
+ * the feature is enabled, but disable_amu can both be used to disable or
+ * enable the capability at runtime in case the default changes in the future.
+ *
+ * To be noted that for security considerations, this does not bypass the
+ * setting of AMUSERENR_EL0 to trap accesses from EL0 (userspace) to EL1
+ * (kernel). Therefore, firmware should still ensure accesses to AMU registers
+ * are not trapped in EL2/EL3.
+ */
+static bool disable_amu;
+
+static int __init set_disable_amu(char *str)
+{
+ int value = 0;
+
+ disable_amu = get_option(&str, &value) ? !!value : true;
+
+ return 0;
+}
+early_param("disable_amu", set_disable_amu);
+
+static bool has_amu(const struct arm64_cpu_capabilities *cap,
+ int __unused)
+{
+ /*
+ * The AMU extension is a non-conflicting feature: the kernel can
+ * safely run a mix of CPUs with and without support for the
+ * activity monitors extension. Therefore, if not disabled through
+ * the kernel command line early parameter, enable the capability
+ * to allow any late CPU to use the feature.
+ *
+ * With this feature enabled, the cpu_enable function will be called
+ * for all CPUs that match the criteria, including secondary and
+ * hotplugged, marking this feature as present on that respective CPU.
+ * The enable function will also print a detection message.
+ */
+
+ if (!disable_amu && !zalloc_cpumask_var(&amu_cpus, GFP_KERNEL)) {
+ pr_err("Activity Monitors Unit (AMU): fail to allocate memory");
+ disable_amu = true;
+ }
+
+ return !disable_amu;
+}
+#endif
+
#ifdef CONFIG_ARM64_VHE
static bool runs_at_el2(const struct arm64_cpu_capabilities *entry, int __unused)
{
@@ -1419,6 +1498,24 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
.cpu_enable = cpu_clear_disr,
},
#endif /* CONFIG_ARM64_RAS_EXTN */
+#ifdef CONFIG_ARM64_AMU_EXTN
+ {
+ /*
+ * The feature is enabled by default if CONFIG_ARM64_AMU_EXTN=y.
+ * Therefore, don't provide .desc as we don't want the detection
+ * message to be shown until at least one CPU is detected to
+ * support the feature.
+ */
+ .capability = ARM64_HAS_AMU_EXTN,
+ .type = ARM64_CPUCAP_WEAK_LOCAL_CPU_FEATURE,
+ .matches = has_amu,
+ .sys_reg = SYS_ID_AA64PFR0_EL1,
+ .sign = FTR_UNSIGNED,
+ .field_pos = ID_AA64PFR0_AMU_SHIFT,
+ .min_field_value = ID_AA64PFR0_AMU,
+ .cpu_enable = cpu_amu_enable,
+ },
+#endif /* CONFIG_ARM64_AMU_EXTN */
{
.desc = "Data cache clean to the PoU not required for I/D coherence",
.capability = ARM64_HAS_CACHE_IDC,
--
2.17.1
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