From: Ionela Voinescu ionela.voinescu@arm.com
commit e89d120c4b720e232cc6a94f0fcbd59c15d41489 upstream.
The AMU counter AMEVCNTR01 (constant counter) should increment at the same rate as the system counter. On affected Cortex-A510 cores, AMEVCNTR01 increments incorrectly giving a significantly higher output value. This results in inaccurate task scheduler utilization tracking and incorrect feedback on CPU frequency.
Work around this problem by returning 0 when reading the affected counter in key locations that results in disabling all users of this counter from using it either for frequency invariance or as FFH reference counter. This effect is the same to firmware disabling affected counters.
Details on how the two features are affected by this erratum:
- AMU counters will not be used for frequency invariance for affected CPUs and CPUs in the same cpufreq policy. AMUs can still be used for frequency invariance for unaffected CPUs in the system. Although unlikely, if no alternative method can be found to support frequency invariance for affected CPUs (cpufreq based or solution based on platform counters) frequency invariance will be disabled. Please check the chapter on frequency invariance at Documentation/scheduler/sched-capacity.rst for details of its effect.
- Given that FFH can be used to fetch either the core or constant counter values, restrictions are lifted regarding any of these counters returning a valid (!0) value. Therefore FFH is considered supported if there is a least one CPU that support AMUs, independent of any counters being disabled or affected by this erratum. Clarifying comments are now added to the cpc_ffh_supported(), cpu_read_constcnt() and cpu_read_corecnt() functions.
The above is achieved through adding a new erratum: ARM64_ERRATUM_2457168.
Signed-off-by: Ionela Voinescu ionela.voinescu@arm.com Reviewed-by: Catalin Marinas catalin.marinas@arm.com Cc: Catalin Marinas catalin.marinas@arm.com Cc: Will Deacon will@kernel.org Cc: James Morse james.morse@arm.com Link: https://lore.kernel.org/r/20220819103050.24211-1-ionela.voinescu@arm.com Signed-off-by: Will Deacon will@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- Documentation/arm64/silicon-errata.rst | 2 ++ arch/arm64/Kconfig | 17 +++++++++++++++++ arch/arm64/kernel/cpu_errata.c | 9 +++++++++ arch/arm64/kernel/cpufeature.c | 5 ++++- arch/arm64/kernel/topology.c | 32 ++++++++++++++++++++++++++++++-- arch/arm64/tools/cpucaps | 1 + 6 files changed, 63 insertions(+), 3 deletions(-)
--- a/Documentation/arm64/silicon-errata.rst +++ b/Documentation/arm64/silicon-errata.rst @@ -94,6 +94,8 @@ stable kernels. +----------------+-----------------+-----------------+-----------------------------+ | ARM | Cortex-A510 | #2441009 | ARM64_ERRATUM_2441009 | +----------------+-----------------+-----------------+-----------------------------+ +| ARM | Cortex-A510 | #2457168 | ARM64_ERRATUM_2457168 | ++----------------+-----------------+-----------------+-----------------------------+ | ARM | Neoverse-N1 | #1188873,1418040| ARM64_ERRATUM_1418040 | +----------------+-----------------+-----------------+-----------------------------+ | ARM | Neoverse-N1 | #1349291 | N/A | --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -683,6 +683,23 @@ config ARM64_ERRATUM_2441009
If unsure, say Y.
+config ARM64_ERRATUM_2457168 + bool "Cortex-A510: 2457168: workaround for AMEVCNTR01 incrementing incorrectly" + depends on ARM64_AMU_EXTN + default y + help + This option adds the workaround for ARM Cortex-A510 erratum 2457168. + + The AMU counter AMEVCNTR01 (constant counter) should increment at the same rate + as the system counter. On affected Cortex-A510 cores AMEVCNTR01 increments + incorrectly giving a significantly higher output value. + + Work around this problem by returning 0 when reading the affected counter in + key locations that results in disabling all users of this counter. This effect + is the same to firmware disabling affected counters. + + If unsure, say Y. + config CAVIUM_ERRATUM_22375 bool "Cavium erratum 22375, 24313" default y --- a/arch/arm64/kernel/cpu_errata.c +++ b/arch/arm64/kernel/cpu_errata.c @@ -551,6 +551,15 @@ const struct arm64_cpu_capabilities arm6 ERRATA_MIDR_ALL_VERSIONS(MIDR_NVIDIA_CARMEL), }, #endif +#ifdef CONFIG_ARM64_ERRATUM_2457168 + { + .desc = "ARM erratum 2457168", + .capability = ARM64_WORKAROUND_2457168, + .type = ARM64_CPUCAP_WEAK_LOCAL_CPU_FEATURE, + /* Cortex-A510 r0p0-r1p1 */ + CAP_MIDR_RANGE(MIDR_CORTEX_A510, 0, 0, 1, 1) + }, +#endif { } }; --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -1736,7 +1736,10 @@ static void cpu_amu_enable(struct arm64_ pr_info("detected CPU%d: Activity Monitors Unit (AMU)\n", smp_processor_id()); cpumask_set_cpu(smp_processor_id(), &amu_cpus); - update_freq_counters_refs(); + + /* 0 reference values signal broken/disabled counters */ + if (!this_cpu_has_cap(ARM64_WORKAROUND_2457168)) + update_freq_counters_refs(); } }
--- a/arch/arm64/kernel/topology.c +++ b/arch/arm64/kernel/topology.c @@ -308,12 +308,25 @@ core_initcall(init_amu_fie);
static void cpu_read_corecnt(void *val) { + /* + * A value of 0 can be returned if the current CPU does not support AMUs + * or if the counter is disabled for this CPU. A return value of 0 at + * counter read is properly handled as an error case by the users of the + * counter. + */ *(u64 *)val = read_corecnt(); }
static void cpu_read_constcnt(void *val) { - *(u64 *)val = read_constcnt(); + /* + * Return 0 if the current CPU is affected by erratum 2457168. A value + * of 0 is also returned if the current CPU does not support AMUs or if + * the counter is disabled. A return value of 0 at counter read is + * properly handled as an error case by the users of the counter. + */ + *(u64 *)val = this_cpu_has_cap(ARM64_WORKAROUND_2457168) ? + 0UL : read_constcnt(); }
static inline @@ -340,7 +353,22 @@ int counters_read_on_cpu(int cpu, smp_ca */ bool cpc_ffh_supported(void) { - return freq_counters_valid(get_cpu_with_amu_feat()); + int cpu = get_cpu_with_amu_feat(); + + /* + * FFH is considered supported if there is at least one present CPU that + * supports AMUs. Using FFH to read core and reference counters for CPUs + * that do not support AMUs, have counters disabled or that are affected + * by errata, will result in a return value of 0. + * + * This is done to allow any enabled and valid counters to be read + * through FFH, knowing that potentially returning 0 as counter value is + * properly handled by the users of these counters. + */ + if ((cpu >= nr_cpu_ids) || !cpumask_test_cpu(cpu, cpu_present_mask)) + return false; + + return true; }
int cpc_read_ffh(int cpu, struct cpc_reg *reg, u64 *val) --- a/arch/arm64/tools/cpucaps +++ b/arch/arm64/tools/cpucaps @@ -54,6 +54,7 @@ WORKAROUND_1418040 WORKAROUND_1463225 WORKAROUND_1508412 WORKAROUND_1542419 +WORKAROUND_2457168 WORKAROUND_CAVIUM_23154 WORKAROUND_CAVIUM_27456 WORKAROUND_CAVIUM_30115