Re: [PATCH v2 1/6] arm64: add support for the AMU extension v1

From: Suzuki Kuruppassery Poulose
Date: Tue Jan 28 2020 - 11:34:30 EST

On 18/12/2019 18:26, Ionela Voinescu wrote:
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
- (while here) create defines for ID_PFR0_EL1 fields when adding
the AMU field information.

Signed-off-by: Ionela Voinescu <ionela.voinescu@xxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
Cc: Marc Zyngier <maz@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
---
arch/arm64/Kconfig | 27 ++++++++++
arch/arm64/include/asm/cpucaps.h | 3 +-
arch/arm64/include/asm/cpufeature.h | 4 ++
arch/arm64/include/asm/sysreg.h | 44 ++++++++++++++++
arch/arm64/kernel/cpufeature.c | 81 +++++++++++++++++++++++++++--
5 files changed, 154 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index ac31ed6184d0..6ae7bfa5812e 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1485,6 +1485,33 @@ 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.
+
+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..b89e799d6972 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -673,6 +673,10 @@ static inline bool cpu_has_hw_af(void)
ID_AA64MMFR1_HADBS_SHIFT);
}
+#ifdef CONFIG_ARM64_AMU_EXTN
+extern inline bool cpu_has_amu_feat(void);
+#endif
+
#endif /* __ASSEMBLY__ */
#endif
diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index 6e919fafb43d..bfcc87953a68 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 CRn op1 op2 CRm
+ * Counter: 11 1101 011 n<2:0> 010:n<3>
+ * Type: 11 1101 011 n<2:0> 011:n<3>
+ * n: 0-3
+ *
+ * Group 1 of activity monitors (auxiliary):
+ * op0 CRn op1 op2 CRm
+ * Counter: 11 1101 011 n<2:0> 110:n<3>
+ * Type: 11 1101 011 n<2:0> 111:n<3>
+ * n: 0-15
+ */
+
+#define SYS_AMEVCNTR0_EL0(n) SYS_AM_EL0(4 + ((n) >> 3), (n) & 0x7)
+#define SYS_AMEVTYPE0_EL0(n) SYS_AM_EL0(6 + ((n) >> 3), (n) & 0x7)
+#define SYS_AMEVCNTR1_EL0(n) SYS_AM_EL0(12 + ((n) >> 3), (n) & 0x7)
+#define SYS_AMEVTYPE1_EL0(n) SYS_AM_EL0(14 + ((n) >> 3), (n) & 0x7)
+
+/* 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
@@ -709,6 +747,12 @@
#define ID_AA64MMFR0_TGRAN16_NI 0x0
#define ID_AA64MMFR0_TGRAN16_SUPPORTED 0x1
+#define ID_PFR0_AMU_SHIFT 20
+#define ID_PFR0_STATE3_SHIFT 12
+#define ID_PFR0_STATE2_SHIFT 8
+#define ID_PFR0_STATE1_SHIFT 4
+#define ID_PFR0_STATE0_SHIFT 0
+
#if defined(CONFIG_ARM64_4K_PAGES)
#define ID_AA64MMFR0_TGRAN_SHIFT ID_AA64MMFR0_TGRAN4_SHIFT
#define ID_AA64MMFR0_TGRAN_SUPPORTED ID_AA64MMFR0_TGRAN4_SUPPORTED
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 04cf64e9f0c9..c639b3e052d7 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),
@@ -314,10 +315,11 @@ static const struct arm64_ftr_bits ftr_id_mmfr4[] = {
};
static const struct arm64_ftr_bits ftr_id_pfr0[] = {
- ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, 12, 4, 0), /* State3 */
- ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, 8, 4, 0), /* State2 */
- ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, 4, 4, 0), /* State1 */
- ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, 0, 4, 0), /* State0 */
+ ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_PFR0_AMU_SHIFT, 4, 0),

Why is this STRICT while the aa64pfr0 field is NON_STRICT ? On the other
hand, do we need this entry ? Do we plan to support 32bit guests using
AMU counters ? If we do, we may need to cap this field for the guests.

Also, fyi, please note that there may be conflicts with another series from Anshuman which cleans up the tables and "naming" the shifts. [1].
[1] purposefully hides the AMU from ID_PFR0 due to the above reasoning.

+ ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_PFR0_STATE3_SHIFT, 4, 0),
+ ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_PFR0_STATE2_SHIFT, 4, 0),
+ ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_PFR0_STATE1_SHIFT, 4, 0),
+ ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_PFR0_STATE0_SHIFT, 4, 0),
ARM64_FTR_END,
};
@@ -1150,6 +1152,59 @@ static bool has_hw_dbm(const struct arm64_cpu_capabilities *cap,
#endif
+#ifdef CONFIG_ARM64_AMU_EXTN
+
+/*
+ * This per cpu variable only signals that the CPU implementation supports
+ * the Activity Monitors Unit (AMU) but does not provide information
+ * regarding all the events that it supports.
+ * When this amu_feat per CPU variable is true, the user of this feature
+ * can only rely on the presence of the 4 fixed counters. But this does
+ * not guarantee that the counters are enabled or access to these counters
+ * is provided by code executed at higher exception levels.
+ *
+ * Also, to ensure the safe use of this per_cpu variable, the following
+ * accessor is defined to allow a read of amu_feat for the current cpu only
+ * from the current cpu.
+ * - cpu_has_amu_feat()
+ */
+static DEFINE_PER_CPU_READ_MOSTLY(u8, amu_feat);
+
+inline bool cpu_has_amu_feat(void)
+{
+ return !!this_cpu_read(amu_feat);
+}
+

minor nit: Or you may use a cpumask_t set of CPUs where AMU is
available. But if you plan to extend this for the future AMU version
tracking the mask may not be sufficient.

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2020-January/708287.html


The rest looks fine to me.

Suzuki